QUIC                                                             M. Duke
Internet-Draft                                         F5 Networks, Inc.
Intended status: Standards Track                                N. Banks
Expires: July 31, August 1, 2020                                        Microsoft
                                                        January 28, 29, 2020

            QUIC-LB: Generating Routable QUIC Connection IDs
                   draft-ietf-quic-load-balancers-00
                   draft-ietf-quic-load-balancers-01

Abstract

   QUIC connection IDs allow continuation of connections across address/
   port 4-tuple changes, and can store routing information for stateless
   or low-state load balancers.  They also can prevent linkability of
   connections across deliberate address migration through the use of
   protected communications between client and server.  This creates
   issues for load-balancing intermediaries.  This specification
   standardizes methods for encoding routing information and proposes an
   optional protocol called QUIC-LB to exchange the parameters given a small
   set of that
   encoding. configuration parameters.  This framework also enables offload
   of other QUIC functions to trusted intermediaries, given the explicit
   cooperation of the QUIC server.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on July 31, August 1, 2020.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Protocol Objectives . . . . . . . . . . . . . . . . . . . . .   5   4
     2.1.  Simplicity  . . . . . . . . . . . . . . . . . . . . . . .   5   4
     2.2.  Security  . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.3.  Robustness to Middleboxes . . . . . . . . . . . . . . . .   6
     2.4.  Load Balancer Chains  . . . . . . . . . . . . . . . . . .   6   5
   3.  First CID octet . . . . . . . . . . . . . . . . . . . . . . .   6   5
     3.1.  Config Rotation . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  Configuration Failover  . . . . . . . . . . . . . . . . .   7   6
     3.3.  Length Self-Description . . . . . . . . . . . . . . . . .   7
   4.  Routing Algorithms  . . . . . . . . . . . . . . . . . . . . .   8   7
     4.1.  Plaintext CID Algorithm . . . . . . . . . . . . . . . . .   9   8
       4.1.1.  Configuration Agent Actions . . . . . . . . . . . . .   8
       4.1.2.  Load Balancer Actions . . . . . . . . . . . . . . . .   9
       4.1.2.
       4.1.3.  Server Actions  . . . . . . . . . . . . . . . . . . .   9
     4.2.  Obfuscated CID Algorithm  . . . . . . . . . . . . . . . .  10   9
       4.2.1.  Configuration Agent Actions . . . . . . . . . . . . .   9
       4.2.2.  Load Balancer Actions . . . . . . . . . . . . . . . .  10
       4.2.2.
       4.2.3.  Server Actions  . . . . . . . . . . . . . . . . . . .  11  10
     4.3.  Stream Cipher CID Algorithm . . . . . . . . . . . . . . .  11  10
       4.3.1.  Configuration Agent Actions . . . . . . . . . . . . .  11
       4.3.2.  Load Balancer Actions . . . . . . . . . . . . . . . .  12
       4.3.2.  11
       4.3.3.  Server Actions  . . . . . . . . . . . . . . . . . . .  12
     4.4.  Block Cipher CID Algorithm  . . . . . . . . . . . . . . .  13  12
       4.4.1.  Configuration Agent Actions . . . . . . . . . . . . .  12
       4.4.2.  Load Balancer Actions . . . . . . . . . . . . . . . .  13
       4.4.2.
       4.4.3.  Server Actions  . . . . . . . . . . . . . . . . . . .  14  13
   5.  Retry Service . . . . . . . . . . . . . . . . . . . . . . . .  14  13
     5.1.  Common Requirements . . . . . . . . . . . . . . . . . . .  15  14
     5.2.  No-Shared-State Retry Service . . . . . . . . . . . . . .  15  14
       5.2.1.  Service Requirements  . . . . . . . . . . . . . . . .  15  14
       5.2.2.  Server Requirements . . . . . . . . . . . . . . . . .  17  16
     5.3.  Shared-State Retry Service  . . . . . . . . . . . . . . .  17  16
       5.3.1.  Service Requirements  . . .  Configuration Agent Actions . . . . . . . . . . . . .  19  18
       5.3.2.  Server  Service Requirements  . . . . . . . . . . . . . . . . .  19
   6.  Configuration  18
       5.3.3.  Server Requirements . . . . . . . . . . . . . . . . .  19
   7.  Protocol Description  18
   6.  Configuration Requirements  . . . . . . . . . . . . . . . . .  18
   7.  Security Considerations . . .  22
     7.1.  Out of band sharing . . . . . . . . . . . . . . . .  20
     7.1.  Attackers not between the load balancer and server  . . .  22  21
     7.2.  QUIC-LB Message Exchange  . . .  Attackers between the load balancer and server  . . . . .  21
   8.  IANA Considerations . . . . . . . .  22
     7.3.  QUIC-LB Packet . . . . . . . . . . . . .  21
   9.  References  . . . . . . . .  22
     7.4.  Message Types and Formats . . . . . . . . . . . . . . . .  23
       7.4.1.  ACK_LB Message .  21
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  24
       7.4.2.  FAIL Message  21
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  22
   Appendix A.  Acknowledgments  . . .  24
       7.4.3.  ROUTING_INFO Message . . . . . . . . . . . . . . .  22
   Appendix B.  Change Log .  24
       7.4.4.  STREAM_CID Message . . . . . . . . . . . . . . . . .  25
       7.4.5.  BLOCK_CID Message . . .  22
     B.1.  since-draft-ietf-quic-load-balancers-00 . . . . . . . . .  22
     B.2.  Since draft-duke-quic-load-balancers-06 . . . . . .  26
       7.4.6.  SERVER_ID Message . . .  22
     B.3.  Since draft-duke-quic-load-balancers-05 . . . . . . . . .  22
     B.4.  Since draft-duke-quic-load-balancers-04 . . . . . .  27
       7.4.7.  MODULUS Message . . .  23
     B.5.  Since draft-duke-quic-load-balancers-03 . . . . . . . . .  23
     B.6.  Since draft-duke-quic-load-balancers-02 . . . . . . .  27
       7.4.8.  PLAINTEXT Message . .  23
     B.7.  Since draft-duke-quic-load-balancers-01 . . . . . . . . .  23
     B.8.  Since draft-duke-quic-load-balancers-00 . . . . . . .  27
       7.4.9.  RETRY_SERVICE_STATELESS message . .  23
   Authors' Addresses  . . . . . . . . .  28
       7.4.10. RETRY_SERVICE_STATEFUL message . . . . . . . . . . .  28
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  28
     8.1.  Outside attackers . . . . . . . . . . . . . . . . . . . .  29
     8.2.  Inside Attackers  . . . . . . . . . . . . . . . . . . . .  29
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  29
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  29
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  30
     10.2.  Informative References . . . . . . . . . . . . . . . . .  30
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  30
   Appendix B.  Change Log . . . . . . . . . . . . . . . . . . . . .  30
     B.1.  Since draft-duke-quic-load-balancers-06 . . . . . . . . .  30
     B.2.  Since draft-duke-quic-load-balancers-05 . . . . . . . . .  30
     B.3.  Since draft-duke-quic-load-balancers-04 . . . . . . . . .  30
     B.4.  Since draft-duke-quic-load-balancers-03 . . . . . . . . .  31
     B.5.  Since draft-duke-quic-load-balancers-02 . . . . . . . . .  31
     B.6.  Since draft-duke-quic-load-balancers-01 . . . . . . . . .  31
     B.7.  Since draft-duke-quic-load-balancers-00 . . . . . . . . .  31
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  31

1.  Introduction

   QUIC packets usually contain a connection ID to allow endpoints to
   associate packets with different address/port 4-tuples to the same
   connection context.  This feature makes connections robust in the
   event of NAT rebinding.  QUIC endpoints usually designate the
   connection ID which peers use to address packets.  Server-generated
   connection IDs create a potential need for out-of-band communication
   to support QUIC.

   QUIC allows servers (or load balancers) to designate an initial
   connection ID to encode useful routing information for load
   balancers.  It also encourages servers, in packets protected by
   cryptography, to provide additional connection IDs to the client.
   This allows clients that know they are going to change IP address or
   port to use a separate connection ID on the new path, thus reducing
   linkability as clients move through the world.

   There is a tension between the requirements to provide routing
   information and mitigate linkability.  Ultimately, because new
   connection IDs are in protected packets, they must be generated at
   the server if the load balancer does not have access to the
   connection keys.  However, it is the load balancer that has the
   context necessary to generate a connection ID that encodes useful
   routing information.  In the absence of any shared state between load
   balancer and server, the load balancer must maintain a relatively
   expensive table of server-generated connection IDs, and will not
   route packets correctly if they use a connection ID that was
   originally communicated in a protected NEW_CONNECTION_ID frame.

   This specification provides a method of coordination between QUIC
   servers and low-state load balancers to support connection IDs that
   encode routing information.  It describes desirable properties of a
   solution, and then specifies a protocol that provides those
   properties.  This protocol supports multiple encoding schemes that
   increase in complexity as they address paths between load balancer
   and server with weaker trust dynamics.

   Aside from load balancing, a QUIC server may also desire to offload
   other protocol functions to trusted intermediaries.  These
   intermediaries might include hardware assist on the server host
   itself, without access to fully decrypted QUIC packets.  For example,
   this document specifies a means of offloading stateless retry to
   counter Denial of Service attacks.  It also proposes a system for
   self-encoding connection ID length in all packets, so that crypto
   offload can consistently look up key information.

1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS.  Lower case uses of these words are not to be
   interpreted as carrying significance described in RFC 2119.

   In this document, "client" and "server" refer to the endpoints of a
   QUIC connection unless otherwise indicated.  A "load balancer" is an
   intermediary for that connection that does not possess QUIC
   connection keys, but it may rewrite IP addresses or conduct other IP
   or UDP processing.

   Note that stateful load balancers that act as proxies, by terminating
   a QUIC connection with the client and then retrieving data from the
   server using QUIC or another protocol, are treated as a server with
   respect to this specification.

   When discussing security threats to QUIC-LB, we distinguish between
   "inside observers" and "outside observers."  The former lie on the
   path between the load balancer and server, which often but not always
   lies inside the server's data center or cloud deployment.  Outside
   observers are on the path between the load balancer and client.
   "Off-path" attackers, though not on any data path, may also be
   "inside" or "outside" depending on whether not they have network
   access to the server without intermediation by the load balancer and/
   or other security devices.

2.  Protocol Objectives

2.1.  Simplicity

   QUIC is intended to provide unlinkability across connection
   migration, but servers are not required to provide additional
   connection IDs that effectively prevent linkability.  If the
   coordination scheme is too difficult to implement, servers behind
   load balancers using connection IDs for routing will use trivially
   linkable connection IDs.  Clients will therefore be forced choose
   between terminating the connection during migration or remaining
   linkable, subverting a design objective of QUIC.

   The solution should be both simple to implement and require little
   additional infrastructure for cryptographic keys, etc.

2.2.  Security

   In the limit where there are very few connections to a pool of
   servers, no scheme can prevent the linking of two connection IDs with
   high probability.  In the opposite limit, where all servers have many
   connections that start and end frequently, it will be difficult to
   associate two connection IDs even if they are known to map to the
   same server.

   QUIC-LB is relevant in the region between these extremes: when the
   information that two connection IDs map to the same server is helpful
   to linking two connection IDs.  Obviously, any scheme that
   transparently communicates this mapping to outside observers
   compromises QUIC's defenses against linkability.

   However, concealing this mapping from inside observers is beyond the
   scope of QUIC-LB.  By simply observing Link-Layer and/or Network-
   Layer addresses of packets containing distinct connection IDs, it is
   trivial to determine that they map to the same server, even if
   connection IDs are entirely random and do not encode routing
   information.  Schemes that conceal these addresses (e.g., IPsec) can
   also conceal QUIC-LB messages.

   Inside observers are generally able to mount Denial of Service (DoS)
   attacks on QUIC connections regardless of Connection ID schemes.
   However, QUIC-LB should protect against Denial of Service due to
   inside off-path attackers in cases where such attackers are possible.

   Though not an explicit goal of the QUIC-LB design, concealing the
   server mapping also complicates attempts to focus attacks on a
   specific server in the pool.

2.3.  Robustness to Middleboxes

   The path between load balancer and server may pass through
   middleboxes that could drop the coordination messages in this
   protocol.  It is therefore advantageous to make messages resemble
   QUIC traffic as much as possible, as any viable path must obviously
   admit QUIC traffic.

2.4.  Load Balancer Chains

   While it is possible to construct a scheme that supports multiple
   low-state load balancers in the path, by using different parts of the
   connection ID to encode routing information for each load balancer,
   this use case is out of scope for QUIC-LB.

3.  First CID octet

   The first octet of a Connection ID is reserved for two special
   purposes, one mandatory (config rotation) and one optional (length
   self-description).

   Subsequent sections of this document refer to the contents of this
   octet as the "first octet."

3.1.  Config Rotation

   The first two bits of any connection-ID MUST encode the configuration
   phase of that ID.  QUIC-LB messages indicate the phase of the
   algorithm and parameters that they encode.

   A new configuration may change one or more parameters of the old
   configuration, or change the algorithm used.

   It is possible for servers to have mutually exclusive sets of
   supported algorithms, or for a transition from one algorithm to
   another to result in Fail Payloads.  The four states encoded in these
   two bits allow two mutually exclusive server pools to coexist, and
   for each of them to transition to a new set of parameters.

   When new configuration is distributed to servers, there will be a
   transition period when connection IDs reflecting old and new
   configuration coexist in the network.  The rotation bits allow load
   balancers to apply the correct routing algorithm and parameters to
   incoming packets.

   Servers MUST NOT generate new connection IDs using an old
   configuration when it has sent an Ack payload for a new
   configuration.

   Load balancers SHOULD NOT use a codepoint to represent a new
   configuration until it takes precautions to make sure that all
   connections using IDs with an old configuration at that codepoint
   have closed or transitioned.  They MAY drop connection IDs with the
   old configuration after a reasonable interval to accelerate this
   process.

3.2.  Configuration Failover

   If a server is configured to expect QUIC-LB messages, and it has not
   received these, it MUST generate connection IDs with the config
   rotation bits set to '11' and MUST use the "disable_migration"
   transport parameter in all new QUIC connections.  It MUST NOT send
   NEW_CONNECTION_ID frames with new values.

   A load balancer that sees a connection ID with config rotation bits
   set to '11' MUST revert to 5-tuple routing.

3.3.  Length Self-Description

   Local hardware cryptographic offload devices may accelerate QUIC
   servers by receiving keys from the QUIC implementation indexed to the
   connection ID.  However, on physical devices operating multiple QUIC
   servers, it is impractical to efficiently lookup these keys if the
   connection ID does not self-encode its own length.

   Note that this is a function of particular server devices and is
   irrelevant to load balancers.  As such, it is not negotiated between
   servers and load balancers.  However, the remaining 6 bits in the
   first octet of the Connection ID are reserved to express the length
   of the following connection ID, not including the first octet.

   A server not using this functionality SHOULD make the six bits appear
   to be random.

4.  Routing Algorithms

   In QUIC-LB, load balancers do not generate individual connection IDs
   to servers.  Instead, they communicate the parameters of an algorithm
   to generate routable connection IDs.

   The algorithms differ in the complexity of configuration at both load
   balancer and server.  Increasing complexity improves obfuscation of
   the server mapping.

   As clients sometimes generate the DCIDs in long headers, these might
   not conform to the expectations of the routing algorithm.  These are
   called "non-compliant DCIDs":

   o  The DCID might not be long enough for the routing algorithm to
      process.

   o  The extracted server mapping might not correspond to an active
      server.

   o  A field that should be all zeroes after decryption may not be so.

   Load balancers MUST forward packets with long headers with non-
   compliant DCIDs to an active server using an algorithm of its own
   choosing.  It need not coordinate this algorithm with the servers.
   The algorithm SHOULD be deterministic over short time scales so that
   related packets go to the same server.  For example, a non-compliant
   DCID might be converted to an integer and divided by the number of
   servers, with the modulus used to forward the packet.  The number of
   servers is usually consistent on the time scale of a QUIC connection
   handshake.

   Load balancers SHOULD drop packets with non-compliant DCIDs in a
   short header.

   Load balancers MUST forward packets with compliant DCIDs to a server
   in accordance with the chosen routing algorithm.

   The load balancer MUST NOT make the routing behavior dependent on any
   bits in the first octet of the QUIC packet header, except the first
   bit, which indicates a long header.  All other bits are QUIC version-
   dependent and intermediaries should not build their design on
   version-specific templates.

   There are situations where a server pool might be operating two or
   more routing algorithms or parameter sets simultaneously.  The load
   balancer uses the first two bits of the connection ID to multiplex
   incoming DCIDs over these schemes.

   This section describes two participants: the load balancer and the
   server.  The load balancer, in this description, generates
   configuration parameters.  Note that in practice a third party
   configuration agent MAY assume this responsibility.

4.1.  Plaintext CID Algorithm

   The Plaintext CID Algorithm makes no attempt to obscure the mapping
   of connections to servers, significantly increasing linkability.  The
   format is depicted in the figure below.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  First octet  |             Server ID (X=8..152)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Any (0..152-X)                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 1: Plaintext CID Format

4.1.1.  Load Balancer Actions

   The load balancer selects a number of bytes of the server connection
   ID (SCID) that it will use to route to a given server, called the
   "routing bytes".  The number of bytes MUST have enough entropy to
   have a different code point for each server.

   The load balancer shares this value with servers, as explained in
   Section 7, along with the value that represents that server.

   On each incoming packet, the load balancer extracts consecutive
   octets, beginning with the second byte.  These bytes represent the
   server ID.

4.1.2.  Server Actions

   The server chooses a connection ID length.  This MUST be at least one
   byte longer than the routing bytes.

   When a server needs a new connection ID, it encodes its assigned
   server ID in consecutive octets beginning with the second.  All other
   bits in the connection ID, except for the first octet, MAY be set to
   any other value.  These other bits SHOULD appear random to observers.

4.2.  Obfuscated CID Algorithm

   The Obfuscated CID Algorithm makes an attempt to obscure the mapping
   of connections to servers to reduce linkability, while not requiring
   true encryption and decryption.  The format is depicted in the figure
   below.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  First octet  |  Mixed routing and non-routing bits (64..152) |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 2: Obfuscated CID Format

4.2.1.  Load Balancer Actions

   The load balancer selects an arbitrary set of bits of the server  23

1.  Introduction

   QUIC packets usually contain a connection ID (SCID) that it will use to route to a given server,
   called the "routing bits".  The number of bits MUST have enough
   entropy allow endpoints to have a different code point for each server, and SHOULD
   have enough entropy so that there are many codepoints for each
   server.

   The load balancer MUST NOT select a routing mask
   associate packets with more than 136
   routing bits set different address/port 4-tuples to 1, which allows for the first octet and up to 2
   octets for server purposes in a maximum-length same
   connection ID.

   The load balancer selects a divisor that MUST be larger than the
   number of servers.  It SHOULD be large enough to accommodate
   reasonable increases context.  This feature makes connections robust in the number of servers.  The divisor MUST be
   an odd integer so certain addition operations do not always produce
   an even number.

   The load balancer also assigns each server a "modulus", an integer
   between 0 and the divisor minus 1.  These MUST be unique for each
   server, and SHOULD be distributed across the entire number space
   between zero and the divisor.

   The load balancer shares these three values with servers, as
   explained in Section 7.

   Upon receipt
   event of a NAT rebinding.  QUIC packet, the load balancer extracts the
   selected bits of the SCID and expresses them as an unsigned integer
   of that length.  The load balancer then divides the result by the
   chosen divisor.  The modulus of this operation maps to the modulus
   for endpoints usually designate the destination server.

   Note that any SCID that contains
   connection ID which peers use to address packets.  Server-generated
   connection IDs create a server's modulus, plus potential need for out-of-band communication
   to support QUIC.

   QUIC allows servers (or load balancers) to designate an
   arbitrary integer multiple of the divisor, in the initial
   connection ID to encode useful routing bits is
   routable information for load
   balancers.  It also encourages servers, in packets protected by
   cryptography, to provide additional connection IDs to that server regardless of the contents of the non-routing
   bits.  Outside observers client.
   This allows clients that do not know the divisor they are going to change IP address or the routing
   bits will therefore have difficulty identifying that two SCIDs route
   port to use a separate connection ID on the same server.

   Note also that not all Connection IDs are necessarily routable, new path, thus reducing
   linkability as clients move through the computed modulus may not match one assigned to any server.  These
   DCIDs are non-compliant as described above.

4.2.2.  Server Actions

   The server chooses world.

   There is a connection ID length.  This MUST contain all of tension between the requirements to provide routing bits
   information and MUST mitigate linkability.  Ultimately, because new
   connection IDs are in protected packets, they must be generated at least 9 octets to provide adequate
   entropy.

   When a
   the server needs a new connection ID, it adds an arbitrary
   nonnegative integer multiple of if the divisor load balancer does not have access to its modulus, without
   exceeding the maximum integer value implied by the number of routing
   bits.  The choice of multiple should appear random within these
   constraints.

   The server encodes
   connection keys.  However, it is the result in load balancer that has the routing bits.  It MAY put any
   other value into bits
   context necessary to generate a connection ID that used neither for encodes useful
   routing nor config
   rotation.  These bits SHOULD appear random to observers.

4.3.  Stream Cipher CID Algorithm

   The Stream Cipher CID algorithm provides true cryptographic
   protection, rather than mere obfuscation, at information.  In the cost absence of additional
   per-packet processing at any shared state between load
   balancer and server, the load balancer to decrypt every incoming must maintain a relatively
   expensive table of server-generated connection IDs, and will not
   route packets correctly if they use a connection ID.  The CID format is depicted below.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  First Octet  |            Nonce (X=64..144)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Encrypted Server ID (Y=8..152-X)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   For that was
   originally communicated in a protected NEW_CONNECTION_ID frame.

   This specification provides common algorithms for encoding the server use (0..152-X-Y)                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 3: Stream Cipher CID Format

4.3.1.  Load Balancer Actions
   mapping in a connection ID given some shared parameters.  The mapping
   is generally only discoverable by observers that have the parameters,
   preserving unlinkability as much as possible.

   Aside from load balancer assigns balancing, a QUIC server may also desire to offload
   other protocol functions to trusted intermediaries.  These
   intermediaries might include hardware assist on the server host
   itself, without access to fully decrypted QUIC packets.  For example,
   this document specifies a server ID means of offloading stateless retry to every server in its pool,
   and determines
   counter Denial of Service attacks.  It also proposes a server system for
   self-encoding connection ID length (in octets) sufficiently large to
   encode in all packets, so that crypto
   offload can consistently look up key information.

   While this document describes a small set of configuration parameters
   to make the server IDs, including potential future servers.

   The mapping intelligible, the means of distributing
   these parameters between load balancer also selects a nonce length balancers, servers, and an 16-octet AES-ECB
   key to use other trusted
   intermediaries is out of its scope.  There are numerous well-known
   infrastructures for connection ID decryption.  The nonce length MUST be at
   least 8 octets and no more than 16 octets. distribution of configuration.

1.1.  Terminology

   The nonce length key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
   server ID length MUST sum "OPTIONAL" in this
   document are to 19 or fewer octets.

   The load balancer shares be interpreted as described in RFC 2119 [RFC2119].

   In this document, these three values words will appear with servers, that interpretation
   only when in ALL CAPS.  Lower case uses of these words are not to be
   interpreted as
   explained carrying significance described in Section 7.

   Upon receipt RFC 2119.

   In this document, "client" and "server" refer to the endpoints of a
   QUIC packet that connection unless otherwise indicated.  A "load balancer" is an
   intermediary for that connection that does not of type Initial or 0-RTT,
   the load balancer extracts as many of the earliest octets from the
   destination possess QUIC
   connection ID keys, but it may rewrite IP addresses or conduct other IP
   or UDP processing.

   Note that stateful load balancers that act as necessary to match proxies, by terminating
   a QUIC connection with the nonce length.
   The server ID immediately follows.

   The load balancer decrypts client and then retrieving data from the
   server ID using 128-bit AES Electronic
   Codebook (ECB) mode, much like QUIC header protection.  The nonce
   octets or another protocol, are zero-padded treated as a server with
   respect to 16 octets.  AES-ECB encrypts this nonce
   using its key specification.

2.  Protocol Objectives

2.1.  Simplicity

   QUIC is intended to generate a mask which it applies provide unlinkability across connection
   migration, but servers are not required to provide additional
   connection IDs that effectively prevent linkability.  If the encrypted
   server id.

   server_id = encrypted_server_id ^ AES-ECB(key, padded-nonce)

   For example, if the nonce length is 10 octets and the server ID
   length
   coordination scheme is 2 octets, the too difficult to implement, servers behind
   load balancers using connection ID can IDs for routing will use trivially
   linkable connection IDs.  Clients will therefore be as small as 13 octets. forced choose
   between terminating the connection during migration or remaining
   linkable, subverting a design objective of QUIC.

   The load balancer uses solution should be both simple to implement and require little
   additional infrastructure for cryptographic keys, etc.

2.2.  Security

   In the limit where there are very few connections to a pool of
   servers, no scheme can prevent the second through eleventh linking of two connection IDs with
   high probability.  In the opposite limit, where all servers have many
   connections that start and end frequently, it will be difficult to
   associate two connection IDs even if they are known to map to the
   same server.

   QUIC-LB is relevant in the
   connection ID for region between these extremes: when the nonce, zero-pads it
   information that two connection IDs map to 16 octets using the
   first 6 octets of the token, and uses same server is helpful
   to linking two connection IDs.  Obviously, any scheme that
   transparently communicates this mapping to decrypt outside observers
   compromises QUIC's defenses against linkability.

   Though not an explicit goal of the QUIC-LB design, concealing the
   server ID mapping also complicates attempts to focus attacks on a
   specific server in the twelfth and thirteenth octet.

   The output of the decryption pool.

2.3.  Load Balancer Chains

   While it is the server ID possible to construct a scheme that the supports multiple
   low-state load balancer
   uses for routing.

4.3.2.  Server Actions

   When generating a routable connection ID, balancers in the server writes arbitrary
   bits into its nonce octets, and its provided server ID into path, by using different parts of the
   server
   connection ID octets.  Servers MAY opt to have encode routing information for each load balancer,
   this use case is out of scope for QUIC-LB.

3.  First CID octet

   The first octet of a longer connection Connection ID
   beyond the nonce and server ID.  The nonce is reserved for two special
   purposes, one mandatory (config rotation) and additional bits MAY
   encode additional information, but SHOULD appear essentially random one optional (length
   self-description).

   Subsequent sections of this document refer to observers.

   The server decrypts the server ID using 128-bit AES Electronic
   Codebook (ECB) mode, much like QUIC header protection. contents of this
   octet as the "first octet."

3.1.  Config Rotation

   The nonce
   octets are zero-padded to 16 octets using first two bits of any connection-ID MUST encode the as many configuration
   phase of that ID.  QUIC-LB messages indicate the first
   octets phase of the token as necessary.  AES-ECB encrypts this nonce using
   its key
   algorithm and parameters that they encode.

   A new configuration may change one or more parameters of the old
   configuration, or change the algorithm used.

   It is possible for servers to generate have mutually exclusive sets of
   supported algorithms, or for a mask which it applies transition from one algorithm to the server id.

   encrypted_server_id = server_id ^ AES-ECB(key, padded-nonce)

4.4.  Block Cipher CID Algorithm
   another to result in Fail Payloads.  The Block Cipher CID Algorithm, by using a full 16 octets of
   plaintext four states encoded in these
   two bits allow two mutually exclusive server pools to coexist, and
   for each of them to transition to a 128-bit cipher, provides higher cryptographic
   protection and detection new set of non-compliant connection IDs.  However,
   it also requires parameters.

   When new configuration is distributed to servers, there will be a
   transition period when connection IDs of at least 17 octets, increasing
   overhead of client-to-server packets.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  First octet  |       Encrypted server ID (X=8..144)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Encrypted Zero Padding (Y=0..144-X)               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Encrypted bits for server use (144-X-Y)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Unencrypted bits for server use (0..24)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 4: Block Cipher CID Format

4.4.1.  Load Balancer Actions reflecting old and new
   configuration coexist in the network.  The rotation bits allow load balancer assigns a server ID
   balancers to every server in its pool, apply the correct routing algorithm and determines parameters to
   incoming packets.

   Servers MUST NOT generate new connection IDs using an old
   configuration when it has sent an Ack payload for a server ID length (in octets) sufficiently large new
   configuration.

   Load balancers SHOULD NOT use a codepoint to
   encode represent a new
   configuration until it takes precautions to make sure that all
   connections using IDs with an old configuration at that codepoint
   have closed or transitioned.  They MAY drop connection IDs with the
   old configuration after a reasonable interval to accelerate this
   process.

3.2.  Configuration Failover

   If a server IDs, including potential future servers.  The
   server ID will start has not received a valid QUIC-LB configuration, and
   believes that low-state, Connection-ID aware load balancers are in
   the second octet of the decrypted path, it SHOULD generate connection
   ID IDs with the config rotation
   bits set to '11' and occupy continuous octets beyond that.

   The SHOULD use the "disable_migration" transport
   parameter in all new QUIC connections.  It SHOULD NOT send
   NEW_CONNECTION_ID frames with new values.

   A load balancer selects that sees a zero-padding length.  This SHOULD be at
   least four octets to allow detection of non-compliant DCIDs.  The
   server connection ID and zero- padding length MUST sum to no more than 16
   octets.  They SHOULD sum to no more than 12 octets, with config rotation bits
   set to provide
   servers adequate space '11' MUST revert to encode their own opaque data.

   The load balancer also selects an 16-octet AES-ECB key 5-tuple routing.

3.3.  Length Self-Description

   Local hardware cryptographic offload devices may accelerate QUIC
   servers by receiving keys from the QUIC implementation indexed to use for the
   connection ID decryption.

   The load balancer shares these four values with servers, as explained
   in Section 7.

   Upon receipt of a ID.  However, on physical devices operating multiple QUIC packet that
   servers, it is impractical to efficiently lookup these keys if the
   connection ID does not self-encode its own length.

   Note that this is a function of type Initial or 0-RTT,
   the particular server devices and is
   irrelevant to load balancer reads balancers.  As such, load balancers MAY omit this
   from their configuration.  However, the remaining 6 bits in the first
   octet to obtain of the config rotation
   bits.  It then decrypts Connection ID are reserved to express the subsequent 16 octets using AES-ECB
   decryption and length of the chosen key.

   The decrypted plaintext contains
   following connection ID, not including the first octet.

   A server id, zero padding, and
   opaque server data in that order.  The not using this functionality SHOULD make the six bits appear
   to be random.

4.  Routing Algorithms

   In QUIC-LB, load balancer uses balancers do not generate individual connection IDs
   to servers.  Instead, they communicate the server
   ID octets for routing.

4.4.2.  Server Actions

   When generating a parameters of an algorithm
   to generate routable connection ID, IDs.

   The algorithms differ in the server MUST choose a
   connection ID length between 17 complexity of configuration at both load
   balancer and 20 octets.  The server writes its
   provided server ID into server.  Increasing complexity improves obfuscation of
   the server ID octets, zeroes into mapping.

   As clients sometimes generate the zero-
   padding octets, and arbitrary bits into DCIDs in long headers, these might
   not conform to the expectations of the remaining bits. routing algorithm.  These
   arbitrary bits MAY encode additional information.  Bits in are
   called "non-compliant DCIDs":

   o  The DCID might not be long enough for the first,
   eighteenth, nineteenth, and twentieth octets SHOULD appear
   essentially random routing algorithm to observers.  The first octet is reserved as
   described in Section 3.
      process.

   o  The extracted server then encrypts the second through seventeenth octets using
   the 128-bit AES-ECB cipher.

5.  Retry Service

   When a server is under load, QUICv1 allows it mapping might not correspond to defer storage an active
      server.

   o  A field that should be all zeroes after decryption may not be so.

   Load balancers MUST forward packets with long headers with non-
   compliant DCIDs to an active server using an algorithm of
   connection state until its own
   choosing.  It need not coordinate this algorithm with the client proves it can receive servers.
   The algorithm SHOULD be deterministic over short time scales so that
   related packets at
   its advertised IP address.  Through go to the use of a Retry packet, same server.  For example, a
   token in subsequent client Initial packets, non-compliant
   DCID might be converted to an integer and divided by the
   original_connection_id transport parameter, number of
   servers, with the modulus used to forward the packet.  The number of
   servers verify address
   ownership and clients verify that there is no "man in usually consistent on the middle"
   generating Retry packets.

   As a trusted Retry Service is literally time scale of a "man QUIC connection
   handshake.

   Load balancers SHOULD drop packets with non-compliant DCIDs in the middle," the
   service must communicate the original_connection_id back a
   short header.

   Load balancers MUST forward packets with compliant DCIDs to the a server so that
   in can pass client verification.  It also must either
   verify the address itself (with accordance with the server trusting this
   verification) or chosen routing algorithm.

   The load balancer MUST NOT make sure there is common context for the server to
   verify routing behavior dependent on any
   bits in the address using first octet of the QUIC packet header, except the first
   bit, which indicates a service-generated token. long header.  All other bits are QUIC version-
   dependent and intermediaries would cannot build their design on
   version-specific templates.

   There are two different mechanisms to allow offload of DoS mitigation
   to situations where a trusted network service.  One requires no shared state; the server need only pool might be configured operating two or
   more routing algorithms or parameter sets simultaneously.  The load
   balancer uses the first two bits of the connection ID to trust a retry service, though this
   imposes other operational constraints. multiplex
   incoming DCIDs over these schemes.

   This section describes three participants: the configuration agent,
   the load balancer, and the server.

4.1.  Plaintext CID Algorithm

   The other requires shared
   key, but has Plaintext CID Algorithm makes no such constraints.

   Retry services MUST forward all non-Initial QUIC packets, as well as
   Initial packets from attempt to obscure the server.

5.1.  Common Requirements

   Regardless mapping
   of mechanism, connections to servers, significantly increasing linkability.  The
   format is depicted in the figure below.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  First octet  |             Server ID (X=8..152)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Any (0..152-X)                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 1: Plaintext CID Format

4.1.1.  Configuration Agent Actions

   The configuration agent selects a retry service has an active mode, where it
   is generating Retry packets, and an inactive mode, where it is not,
   based on its assessment number of bytes of the server load and
   connection ID (SCID) to encode individual server IDs, called the likelihood an attack
   is underway.
   "routing bytes".  The choice number of mode MAY be made on a per-packet basis,
   through a stochastic process or based on client address.

   A retry service bytes MUST forward all packets have enough entropy to
   have a different code point for each server.

   It also assigns a QUIC version it does
   not understand.  Note that if servers support versions server ID to each server.

4.1.2.  Load Balancer Actions

   On each incoming packet, the retry
   service does not, this may unacceptably increase loads on load balancer extracts consecutive
   octets, beginning with the
   servers.  However, dropping these packets would introduce chokepoints
   to block deployment of new QUIC versions.  Note that future versions
   of QUIC might not have Retry packets, or require different
   information.

5.2.  No-Shared-State Retry Service

   The no-shared-state retry service requires no coordination, except
   that second octet.  These bytes represent the
   server must be configured to accept this service. ID.

4.1.3.  Server Actions

   The
   scheme uses server chooses a connection ID length.  This MUST be at least one
   byte longer than the routing bytes.

   When a server needs a new connection ID, it encodes its assigned
   server ID in consecutive octets beginning with the second.  All other
   bits in the first bit of connection ID, except for the token to distinguish between tokens
   from Retry packets (codepoint '0') and tokens from NEW_TOKEN frames
   (codepoint '1').

5.2.1.  Service Requirements

   A no-shared-state retry service MUST first octet, MAY be present on all paths from
   potential clients set to the server.
   any other value.  These paths MUST fail other bits SHOULD appear random to pass QUIC
   traffic should the service fail for any reason.  That is, if the
   service is not operational, observers.

4.2.  Obfuscated CID Algorithm

   The Obfuscated CID Algorithm makes an attempt to obscure the server MUST NOT be exposed mapping
   of connections to client
   traffic.  Otherwise, servers that have already disabled their Retry
   capability would be vulnerable to attack.

   The path between service and server MUST be free of any potential
   attackers.  Note that this reduce linkability, while not requiring
   true encryption and other requirements above severely
   restrict the operational conditions decryption.  The format is depicted in which a no-shared-state retry
   service can safely operate.

   Retry tokens generated by the service MUST have the format figure
   below.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0| ODCIL (7) |  Original Destination Connection ID (0..160)    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Original Destination Connection ID (...)
   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  First octet  |                     Opaque Data (variable)  Mixed routing and non-routing bits (64..152) |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 5: 2: Obfuscated CID Format

4.2.1.  Configuration Agent Actions

   The configuration agent selects an arbitrary set of non-shared-state retry service tokens bits of the
   server connection ID (SCID) that it will use to route to a given
   server, called the "routing bits".  The number of bits MUST have
   enough entropy to have a different code point for each server, and
   SHOULD have enough entropy so that there are many codepoints for each
   server.

   The first bit of retry tokens generated by configuration agent MUST NOT select a routing mask with more than
   136 routing bits set to 1, which allows for the service must be zero. first octet and up to
   2 octets for server purposes in a maximum-length connection ID.

   The token has configuration agent selects a divisor that MUST be larger than
   the following additional fields:

   ODCIL: The length number of servers.  It SHOULD be large enough to accommodate
   reasonable increases in the original destination connection ID from number of servers.  The divisor MUST be
   an odd integer so certain addition operations do not always produce
   an even number.

   The configuration agent also assigns each server a "modulus", an
   integer between 0 and the
   triggering Initial packet.  This is in cleartext to divisor minus 1.  These MUST be readable unique for
   the
   each server, but authenticated later in and SHOULD be distributed across the token.

   Original Destination Connection ID: This also in cleartext entire number space
   between zero and
   authenticated later.

   Opaque Data: This data MUST contain encrypted information the divisor.

4.2.2.  Load Balancer Actions

   Upon receipt of a QUIC packet, the load balancer extracts the
   selected bits of the SCID and expresses them as an unsigned integer
   of that allows length.  The load balancer then divides the retry service result by the
   chosen divisor.  The modulus of this operation maps to validate the client's IP address, in accordance
   with modulus
   for the QUIC specification.  It MUST also encode destination server.

   Note that any SCID that contains a secure hash server's modulus, plus an
   arbitrary integer multiple of the original destination connection ID field divisor, in the routing bits is
   routable to verify that this
   field has not been edited.

   Upon receipt server regardless of an Initial packet with a token the contents of the non-routing
   bits.  Outside observers that begins with '0', do not know the retry service MUST validate divisor or the token in accordance with routing
   bits will therefore have difficulty identifying that two SCIDs route
   to the QUIC
   specification.  It must same server.

   Note also verify that not all Connection IDs are necessarily routable, as
   the secure hash of the
   Connect computed modulus may not match one assigned to any server.  These
   DCIDs are non-compliant as described above.

4.2.3.  Server Actions

   The server chooses a connection ID is correct.  If incorrect, the token is invalid.

   In active mode, the service length.  This MUST issue Retry packets for all Client
   initial packets that contain no token, or all of
   the routing bits and MUST be at least 9 octets to provide adequate
   entropy.

   When a token that has server needs a new connection ID, it adds an arbitrary
   nonnegative integer multiple of the first
   bit set divisor to '1'.  It MUST NOT forward its modulus, without
   exceeding the packet maximum integer value implied by the number of routing
   bits.  The choice of multiple should appear random within these
   constraints.

   The server encodes the result in the routing bits.  It MAY put any
   other value into bits that used neither for routing nor config
   rotation.  These bits SHOULD appear random to observers.

4.3.  Stream Cipher CID Algorithm

   The Stream Cipher CID algorithm provides true cryptographic
   protection, rather than mere obfuscation, at the server.  The
   service MUST validate all tokens with cost of additional
   per-packet processing at the first bit set load balancer to '0'.  If
   successful, the service MUST forward the packet with the token
   intact.  If unsuccessful, it MUST drop the packet.

   Note that this scheme has a performance drawback.  When the retry
   service decrypt every incoming
   connection ID.  The CID format is in active mode, clients with a token from a NEW_TOKEN
   frame will suffer depicted below.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  First Octet  |            Nonce (X=64..144)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Encrypted Server ID (Y=8..152-X)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   For server use (0..152-X-Y)                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 3: Stream Cipher CID Format

4.3.1.  Configuration Agent Actions

   The configuration agent assigns a 1-RTT penalty even though it has proof of address
   with server ID to every server in its token.

   In inactive mode, the service MUST forward all packets that have no
   token or
   pool, and determines a token with the first bit set server ID length (in octets) sufficiently
   large to '1'.  It MUST validate encode all
   tokens with the first bit set server IDs, including potential future servers.

   The configuration agent also selects a nonce length and an 16-octet
   AES-ECB key to '0'.  If successful, the service use for connection ID decryption.  The nonce length
   MUST forward the packet with the token intact.  If unsuccessful, it be at least 8 octets and no more than 16 octets.  The nonce
   length and server ID length MUST either drop the sum to 19 or fewer octets.

4.3.2.  Load Balancer Actions

   Upon receipt of a QUIC packet that is not of type Initial or forward it with 0-RTT,
   the token removed.
   The latter requires decryption and re-encryption load balancer extracts as many of the entire
   Initial packet earliest octets from the
   destination connection ID as necessary to avoid authentication failure.  Forwarding match the
   packet causes nonce length.
   The server ID immediately follows.

   The load balancer decrypts the server ID using 128-bit AES Electronic
   Codebook (ECB) mode, much like QUIC header protection.  The nonce
   octets are zero-padded to respond without the
   original_connection_id transport parameter, 16 octets.  AES-ECB encrypts this nonce
   using its key to generate a mask which preserves the
   normal QUIC signal it applies to the client that there encrypted
   server id.

   server_id = encrypted_server_id ^ AES-ECB(key, padded-nonce)

   For example, if the nonce length is an unauthorized man in 10 octets and the middle.

5.2.2.  Server Requirements

   A server behind a non-shared-state retry service MUST NOT send Retry
   packets.

   Tokens sent in NEW_TOKEN frames MUST have ID
   length is 2 octets, the first bit connection ID can be set to
   '1'.

   If a server receives an Initial Packet with as small as 13 octets.
   The load balancer uses the first bit set to '1',
   it could be from a server-generated NEW_TOKEN frame and should be
   processed in accordance with the QUIC specification.  If a server
   receives an Initial Packet with second through eleventh of the first bit to '0',
   connection ID for the nonce, zero-pads it is a Retry
   token to 16 octets using the
   first 6 octets of the token, and uses this to decrypt the server MUST NOT attempt to validate it.  Instead, it
   MUST assume ID
   in the address is validated twelfth and MUST extract thirteenth octet.

   The output of the Original
   Destination Connection ID, assuming decryption is the format described in
   Section 5.2.1.

5.3.  Shared-State Retry Service

   A shared-state retry service server ID that the load balancer
   uses for routing.

4.3.3.  Server Actions

   When generating a shared key, so that routable connection ID, the server
   can decode the service's retry tokens.  It does not require that all
   traffic pass through writes arbitrary
   bits into its nonce octets, and its provided server ID into the Retry service, so servers
   server ID octets.  Servers MAY send Retry
   packets in response opt to Initial packets that don't include have a valid
   token.

   Both longer connection ID
   beyond the nonce and server ID.  The nonce and service must have access additional bits MAY
   encode additional information, but SHOULD appear essentially random
   to Universal time, though
   tight synchronization is not necessary.

   All tokens, generated by either the observers.

   The server or retry service, MUST use
   the following format.  This format is the cleartext version.  On decrypts the
   wire, these fields server ID using 128-bit AES Electronic
   Codebook (ECB) mode, much like QUIC header protection.  The nonce
   octets are encrypted zero-padded to 16 octets using an AES-ECB cipher and the
   token key.  If as many of the first
   octets of the token is not as necessary.  AES-ECB encrypts this nonce using
   its key to generate a mask which it applies to the server id.

   encrypted_server_id = server_id ^ AES-ECB(key, padded-nonce)

4.4.  Block Cipher CID Algorithm

   The Block Cipher CID Algorithm, by using a multiple of full 16 octets of
   plaintext and a 128-bit cipher, provides higher cryptographic
   protection and detection of non-compliant connection IDs.  However,
   it also requires connection IDs of at least 17 octets, the last
   block is padded with zeroes. increasing
   overhead of client-to-server packets.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    ODCIL  First octet  |   Original Destination Connection       Encrypted server ID (0..160)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             ... (X=8..144)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                      Client IP Address (128)                  +
   |                                                               |
   +                                                               +
   |             Encrypted Zero Padding (Y=0..144-X)               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                                                               +
   |                         date-time (160)                       |
   +                                                               +
   |                                                               |
   +                                                               +
   |           Encrypted bits for server use (144-X-Y)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Opaque Data (optional)           Unencrypted bits for server use (0..24)             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 6: Cleartext format of shared-state retry tokens

   The tokens have the following fields:

   ODCIL: 4: Block Cipher CID Format

4.4.1.  Configuration Agent Actions

   The original destination connection configuration agent assigns a server ID length.  Tokens in
   NEW_TOKEN frames SHOULD set this field to zero.

   Original Destination Connection ID: This is copied from the field every server in
   the client Initial packet.

   Client IP Address: The source IP address from the triggering Initial
   packet. its
   pool, and determines a server ID length (in octets) sufficiently
   large to encode all server IDs, including potential future servers.

   The client IP address is 16 octets.  If an IPv4 address, server ID will start in the
   last 12 octets are zeroes.

   date-time: The date-time string is a total second octet of 20 octets and encodes
   the time the token was generated. decrypted
   connection ID and occupy continuous octets beyond that.

   The format of date-time is
   described in Section 5.6 of [RFC3339]. configuration agent selects a zero-padding length.  This ASCII field MUST use the
   "Z" character for time-offset.

   Opaque Data: SHOULD
   be at least four octets to allow detection of non-compliant DCIDs.
   The server may use this field ID and zero- padding length MUST sum to encode additional
   information, such as congestion window, RTT, or MTU.  Opaque data no more than 16
   octets.  They SHOULD also allow sum to no more than 12 octets, to provide
   servers adequate space to encode their own opaque data.

   The configuration agent also selects an 16-octet AES-ECB key to distinguish between retry tokens (which
   trigger use
   for connection ID decryption.

4.4.2.  Load Balancer Actions

   Upon receipt of the original_connection_id transport parameter) and
   NEW_TOKEN frame tokens.

5.3.1.  Service Requirements

   The service MUST share a "token key" with all supported servers.

   When in active mode, QUIC packet, the service MUST generate Retry tokens with load balancer reads the
   format described above when it receives a client Initial packet with
   no token.

   In active mode, first
   octet to obtain the service SHOULD decrypt incoming tokens. config rotation bits.  It then decrypts the
   subsequent 16 octets using AES-ECB decryption and the chosen key.

   The
   service SHOULD drop packets with an IP address that does not match, decrypted plaintext contains the server id, zero padding, and SHOULD forward packets
   opaque server data in that do, regardless of order.  The load balancer uses the other fields.

   In inactive mode, server
   ID octets for routing.

4.4.3.  Server Actions

   When generating a routable connection ID, the service SHOULD forward all packets to server MUST choose a
   connection ID length between 17 and 20 octets.  The server writes its
   provided server ID into the server so that ID octets, zeroes into the server can issue an up-to-date token to zero-
   padding octets, and arbitrary bits into the
   client.

5.3.2.  Server Requirements

   The server MUST validate all tokens that arrive remaining bits.  These
   arbitrary bits MAY encode additional information.  Bits in Initial packets,
   as they may have bypassed the Retry service.  It first,
   eighteenth, nineteenth, and twentieth octets SHOULD use the date-
   time field appear
   essentially random to apply its expiration limits for tokens.  This need not
   be synchronized with the retry service.  However, servers MAY allow
   retry tokens marked observers.  The first octet is reserved as being a few seconds
   described in Section 3.

   The server then encrypts the future, due to
   possible clock synchronization issues.

   A second through seventeenth octets using
   the 128-bit AES-ECB cipher.

5.  Retry Service

   When a server MUST NOT send is under load, QUICv1 allows it to defer storage of
   connection state until the client proves it can receive packets at
   its advertised IP address.  Through the use of a Retry packet packet, a
   token in response to an subsequent client Initial
   packet that contains a retry token.

6.  Configuration Requirements

   QUIC-LB strives to minimize packets, and the configuration load to enable, as much
   as possible, a "plug-and-play" model.  However, there are some
   configuration requirements based on algorithm
   original_connection_id transport parameter, servers verify address
   ownership and protocol choices
   above.

   If clients verify that there is any in-band communication, servers MUST be explicitly
   configured with the token of no "man in the load balancer they expect to
   interface with.

   The load balancer and server MUST agree on middle"
   generating Retry packets.

   As a routing algorithm and trusted Retry Service is literally a "man in the middle," the
   service must communicate the relevant parameters for original_connection_id back to the
   server so that algorithm.

   For Plaintext CID Routing, this consists of in can pass client verification.  It also must either
   verify the Server ID and address itself (with the
   routing bytes.  The Server ID server trusting this
   verification) or make sure there is unique common context for the server to each server, and
   verify the
   routing bytes address using a service-generated token.

   There are global.

   For Obfuscated CID Routing, this consists of the Routing Bits,
   Divisor, and Modulus.  The Modulus is unique two different mechanisms to each server, but the
   others MUST be global.

   For Stream Cipher CID Routing, this consists allow offload of the Server ID, Server
   ID Length, Key, and Nonce Length.  The Server ID is unique DoS mitigation
   to each
   server, but a trusted network service.  One requires no shared state; the others MUST be global.  The authentication token MUST
   server need only be distributed out of band for this algorithm configured to operate.

   For Block Cipher CID Routing, trust a retry service, though this consists of the Server ID, Server
   ID Length, Key, and Zero-Padding Length.
   imposes other operational constraints.  The Server ID is unique to
   each server, other requires shared
   key, but the others MUST be global.

   A full QUIC-LB configuration has no such constraints.

   Retry services MUST also specify the information
   content of the first CID octet and forward all non-Initial QUIC packets, as well as
   Initial packets from the presence and mode server.

5.1.  Common Requirements

   Regardless of any Retry
   Service.

   The following pseudocode depicts the data items necessary to store mechanism, a
   full QUIC-LB configuration at the server.  It retry service has an active mode, where it
   is meant to describe
   the conceptual range generating Retry packets, and not specify the presentation an inactive mode, where it is not,
   based on its assessment of such
   configuration in server load and the likelihood an internet packet. attack
   is underway.  The comments signify the range choice of acceptable values where applicable.

   uint2    config_rotation_bits;
   enum     { in_band_config, out_of_band_config } config_method;
   select (config_method) {
       case in_band_config: uint64 config_token;
       case out_of_band_config: null;
   } config-method
   boolean  first_octet_encodes_cid_length;
   enum     { none, non_shared_state, shared_state } retry_service;
   select (retry_service) {
       case none: null;
       case non_shared_state: null;
       case shared_state: uint8 key[16];
   } retry_service_config;
   enum     { none, plaintext, obfuscated, stream_cipher, block_cipher }
                     routing_algorithm;
   select (routing_algorithm) {
       case none: null;
       case plaintext: struct {
           uint8 server_id_length; /* 1..19 */
           uint8 server_id[server_id_length];
       } plaintext_config;
       case obfuscated: struct {
           uint8  routing_bit_mask[19];
           uint16 divisor; /* Must mode MAY be odd */
           uint16 modulus; /* 0..(divisor - 1) */
       } obfuscated_config;
       case stream_cipher: struct {
           uint8  nonce_length; /* 8..16 */
           uint8  server_id_length; /* 1..(19 - nonce_length) */
           uint8  server_id[server_id_length];
           uint8  key[16];
       } stream_cipher_config;
       case block_cipher: struct {
           uint8  server_id_length;
           uint8  zero_padding_length; /* 0..(16 - server_id_length) */
           uint8  server_id[server_id_length];
           uint8  key[16];
       } block_cipher_config;
  } routing_algorithm_config;

   This specification allows for out-of-band dissemination of this
   configuration items, but also provides an in-band method made on a per-packet basis,
   through a stochastic process or based on client address.

   A retry service MUST forward all packets for
   deployment models that need it.

7.  Protocol Description

   There are multiple means of configuration a QUIC version it does
   not understand.  Note that correspond if servers support versions the retry
   service does not, this may unacceptably increase loads on the
   servers.  However, dropping these packets would introduce chokepoints
   to
   differing block deployment models and increasing levels of concern about
   the security new QUIC versions.  Note that future versions
   of QUIC might not have Retry packets, or require different
   information.

5.2.  No-Shared-State Retry Service

   The no-shared-state retry service requires no coordination, except
   that the load balancer-server path.

7.1.  Out of band sharing

   When there are concerns about server must be configured to accept this service.  The
   scheme uses the integrity first bit of the path token to distinguish between load
   balancer tokens
   from Retry packets (codepoint '0') and server, operators MAY share routing information using an
   out-of-band technique, which is out of the scope of this
   specification.

   To simplify configuration, the global parameters can tokens from NEW_TOKEN frames
   (codepoint '1').

5.2.1.  Service Requirements

   A no-shared-state retry service MUST be shared out-
   of-band, while the load balancer sends the unique server IDs via present on all paths from
   potential clients to the
   truncated message formats presented below.

7.2.  QUIC-LB Message Exchange

   QUIC-LB load balancers and servers exchange messages via server.  These paths MUST fail to pass QUIC
   traffic should the QUIC-
   LBv1 protocol, which uses service fail for any reason.  That is, if the QUIC invariants with version number
   0xF1000000.  The QUIC-LB load balancers send
   service is not operational, the encoding parameters server MUST NOT be exposed to client
   traffic.  Otherwise, servers and periodically retransmit until that have already disabled their Retry
   capability would be vulnerable to attack.

   The path between service and server responds
   with an acknowledgement.  Specifics MUST be free of any potential
   attackers.  Note that this retransmission are
   implementation-dependent.

7.3.  QUIC-LB Packet

   A QUIC-LB packet uses a long header.  It carries configuration
   information from the load balancer and acknowledgements from other requirements above severely
   restrict the
   servers.  They are sent when a load balancer boots up, detects a new
   server operational conditions in which a no-shared-state retry
   service can safely operate.

   Retry tokens generated by the pool or needs to update service MUST have the server configuration. format below.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+
   |1|C R| Reserved|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0| ODCIL (7) |                        Version (32)  Original Destination Connection ID (0..160)    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  0x00 | 0x00           Original Destination Connection ID (...)            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                  Authentication Token (64)                    +
   |                                                               |
   ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Message Type                     Opaque Data (variable)                    |
   +-+-+-+-+-+-+-+-+
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 7: QUIC-LB Packet 5: Format of non-shared-state retry service tokens

   The Version field allows QUIC-LB to use first bit of retry tokens generated by the Version Negotiation
   mechanism.  All messages in this specification are specific to QUIC-
   LBv1.  It should service must be set to 0xF1000000.

   Load balancers MUST cease sending QUIC-LB packets of this version to
   a server when that server sends a Version Negotiation packet that
   does not advertise zero.
   The token has the version. following additional fields:

   ODCIL: The length of the DCIL and SCIL fields are 0x00.

   CR The 2-bit CR field indicates original destination connection ID from the Config Rotation described in
      Section 3.1.

   Authentication Token  The Authentication Token
   triggering Initial packet.  This is an 8-byte field in cleartext to be readable for
   the server, but authenticated later in the token.

   Original Destination Connection ID: This also in cleartext and
   authenticated later.

   Opaque Data: This data MUST contain encrypted information that both entities obtain at configuration time. allows
   the retry service to validate the client's IP address, in accordance
   with the QUIC specification.  It is used MUST also encode a secure hash of
   the original destination connection ID field to verify that the sender is this
   field has not been edited.

   Upon receipt of an inside off-path attacker.
      Servers and load balancers SHOULD silently discard QUIC-LB packets Initial packet with an incorrect token.

   Message Type  The Message Type indicates a token that begins with '0',
   the type of message payload retry service MUST validate the token in accordance with the QUIC
   specification.  It must also verify that follows the QUIC-LB header.

7.4.  Message Types and Formats

   As described in Section 7.3, QUIC-LB secure hash of the
   Connect ID is correct.  If incorrect, the token is invalid.

   In active mode, the service MUST issue Retry packets for all Client
   initial packets that contain no token, or a single
   message.  This section describes the format and semantics of the
   QUIC-LB message types.

7.4.1.  ACK_LB Message

   A server uses token that has the ACK_LB message (type=0x00) first
   bit set to acknowledge a QUIC-LB '1'.  It MUST NOT forward the packet received from to the load balancer. server.  The ACK-LB message has no
   additional payload beyond
   service MUST validate all tokens with the QUIC-LB packet header.

   Load balancers SHOULD continue first bit set to retransmit a QUIC-LB '0'.  If
   successful, the service MUST forward the packet until with the token
   intact.  If unsuccessful, it MUST drop the packet.

   Note that this scheme has a
   valid ACK_LB message, FAIL message or Version Negotiation Packet performance drawback.  When the retry
   service is
   received in active mode, clients with a token from a NEW_TOKEN
   frame will suffer a 1-RTT penalty even though it has proof of address
   with its token.

   In inactive mode, the server.

7.4.2.  FAIL Message

   A server uses service MUST forward all packets that have no
   token or a token with the FAIL message (type=0x01) first bit set to indicate '1'.  It MUST validate all
   tokens with the
   configuration received from first bit set to '0'.  If successful, the load balancer is unsupported.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Supp. Type  |  Supp. Type   |  ...
   +-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Servers service
   MUST send a FAIL message upon receipt of a message type which
   they do not support, or if they do not possess all of forward the packet with the token intact.  If unsuccessful, it
   MUST either drop the implied
   out-of-band configuration to support a particular message type. packet or forward it with the token removed.
   The payload latter requires decryption and re-encryption of the FAIL message consists of a list of all entire
   Initial packet to avoid authentication failure.  Forwarding the message
   types supported by
   packet causes the server.

   Upon receipt of server to respond without the
   original_connection_id transport parameter, which preserves the
   normal QUIC signal to the client that there is an unauthorized man in
   the middle.

5.2.2.  Server Requirements

   A server behind a FAIL message, Load Balancers non-shared-state retry service MUST either NOT send a
   QUIC-LB message Retry
   packets.

   Tokens sent in NEW_TOKEN frames MUST have the first bit be set to
   '1'.

   If a server supports or remove receives an Initial Packet with the server first bit set to '1',
   it could be from a server-generated NEW_TOKEN frame and should be
   processed in accordance with the QUIC specification.  If a server pool.

7.4.3.  ROUTING_INFO Message

   A load balancer uses
   receives an Initial Packet with the ROUTING_INFO message (type=0x02) first bit to exchange
   all the parameters for the Obfuscated CID algorithm.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                       Routing Bit Mask (152)                  +
   |                                                               |
   +                                                               +
   |                                                               |
   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |         Modulus (16)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Divisor (16)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Routing Bit Mask  The Routing Bit Mask encodes '0', it is a '1' at every bit
      position in Retry
   token and the server connection ID that will encode routing
      information.

   These bits, along with MUST NOT attempt to validate it.  Instead, it
   MUST assume the address is validated and MUST extract the Modulus and Divisor, are chosen by Original
   Destination Connection ID, assuming the
   load balancer as format described in
   Section 4.2.

7.4.4.  STREAM_CID Message 5.2.1.

5.3.  Shared-State Retry Service

   A load balancer shared-state retry service uses a shared key, so that the STREAM_CID message (type=0x03) to exchange
   all server
   can decode the parameters for using Stream Cipher CIDs.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Nonce Len (8) |    SIDL (8)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Server ID (variable)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                             Key (128)                         +
   |                                                               |
   +                                                               +
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 8: Stream CID Payload

   Nonce Len  The Nonce Len field is a one-octet unsigned integer service's retry tokens.  It does not require that
      describes all
   traffic pass through the nonce length necessary to use this routing
      algorithm, Retry service, so servers MAY send Retry
   packets in octets.

   SIDL  The SIDL field is a one-octet unsigned integer response to Initial packets that describes
      the don't include a valid
   token.

   Both server ID length necessary and service must have access to use this routing algorithm, in
      octets.

   Server ID  The Server ID Universal time, though
   tight synchronization is not necessary.

   All tokens, generated by either the unique value assigned to server or retry service, MUST use
   the
      receiving server.  Its length following format.  This format is determined by the SIDL field.

   Key  The Key is an 16-octet field that contains cleartext version.  On the key that
   wire, these fields are encrypted using an AES-ECB cipher and the load
      balancer will use to decrypt server IDs on QUIC packets.  See
      Section 8 to understand why sending keys in plaintext may be a
      safe strategy.

7.4.5.  BLOCK_CID Message

   A load balancer uses
   token key.  If the BLOCK_CID message (type=0x04) to exchange
   all token is not a multiple of 16 octets, the parameters for using Stream Cipher CIDs. last
   block is padded with zeroes.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   ZP Len (8)    ODCIL    |    SIDL (8)   Original Destination Connection ID (0..160)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Server ID (variable)                             ...                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                             Key                                                               +
   |                                                               |
   +                      Client IP Address (128)                  +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                                                               +
   |                         date-time (160)                       |
   +                                                               +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Opaque Data (optional)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

          Figure 9: Block CID Payload

   ZP Len 6: Cleartext format of shared-state retry tokens

   The tokens have the following fields:

   ODCIL: The original destination connection ID length.  Tokens in
   NEW_TOKEN frames SHOULD set this field to zero.

   Original Destination Connection ID: This is copied from the field in
   the client Initial packet.

   Client IP Address: The source IP address from the triggering Initial
   packet.  The client IP address is 16 octets.  If an IPv4 address, the
   last 12 octets are zeroes.

   date-time: The date-time string is a total of 20 octets and encodes
   the time the token was generated.  The format of date-time is
   described in Section 5.6 of [RFC3339].  This ASCII field MUST use the
   "Z" character for time-offset.

   Opaque Data: The server may use this field to encode additional
   information, such as congestion window, RTT, or MTU.  Opaque data
   SHOULD also allow servers to distinguish between retry tokens (which
   trigger use of the original_connection_id transport parameter) and
   NEW_TOKEN frame tokens.

5.3.1.  Configuration Agent Actions

   The configuration agent generates and distributes a "token key."

5.3.2.  Service Requirements

   When in active mode, the service MUST generate Retry tokens with the
   format described above when it receives a client Initial packet with
   no token.

   In active mode, the service SHOULD decrypt incoming tokens.  The ZP Len field is a one-octet unsigned integer
   service SHOULD drop packets with an IP address that
      describes does not match,
   and SHOULD forward packets that do, regardless of the zero-padding length necessary other fields.

   In inactive mode, the service SHOULD forward all packets to use this routing
      algorithm, in octets.

   SIDL  The SIDL field is a one-octet unsigned integer the
   server so that describes the server ID length necessary can issue an up-to-date token to use this routing algorithm, in
      octets. the
   client.

5.3.3.  Server ID Requirements

   The Server ID is the unique value assigned to server MUST validate all tokens that arrive in Initial packets,
   as they may have bypassed the
      receiving server.  Its length is determined by Retry service.  It SHOULD use the SIDL field.

   Key  The Key is an 16-octet date-
   time field that contains to apply its expiration limits for tokens.  This need not
   be synchronized with the key that retry service.  However, servers MAY allow
   retry tokens marked as being a few seconds in the load
      balancer will use future, due to decrypt
   possible clock synchronization issues.

   A server IDs on QUIC packets.  See
      Section 8 to understand why sending keys MUST NOT send a Retry packet in plaintext may be response to an Initial
   packet that contains a
      safe strategy.

7.4.6.  SERVER_ID Message

   A load balancer uses the SERVER_ID message (type=0x05) retry token.

6.  Configuration Requirements

   QUIC-LB requires common configuration to exchange synchronize understanding of
   encodings and guarantee explicit server IDs.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    SIDL (8)   |       Server ID (variable)    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Load balancers send consent of the SERVER_ID message when all global values for
   Stream or Block CIDs are sent out-of-band, so that only server.

   The load balancer and server MUST agree on a routing algorithm and
   the server-
   unique values must be sent in-band.  It also provides all necessary
   paramters relevant parameters for that algorithm.

   For Plaintext CIDs.  The fields are identical to their
   counterparts in CID Routing, this consists of the Section 7.4.4 payload.

7.4.7.  MODULUS Message

   A load balancer uses Server ID and the MODULUS message (type=0x06)
   routing bytes.  The Server ID is unique to exchange just
   the modulus used in each server, and the
   routing bytes are global.

   For Obfuscated CID algorithm.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Modulus (16)        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Load balancers send the MODULUS when all global values for Obfuscated
   CIDs are sent out-of-band, so that only Routing, this consists of the server-unique values must
   be sent in-band. Routing Bits,
   Divisor, and Modulus.  The Modulus field is identical to its counterpart
   in the ROUTING_INFO message.

7.4.8.  PLAINTEXT Message

   A load balancer uses the PLAINTEXT message (type=0x07) unique to exchange
   all parameters needed for each server, but the Plaintext
   others MUST be global.

   For Stream Cipher CID algorithm.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   SIDL (8)  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   + Routing, this consists of the Server ID, Server
   ID (variable)                     +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Length, Key, and Nonce Length.  The SIDL field indicates Server ID is unique to each
   server, but the length others MUST be global.  The authentication token MUST
   be distributed out of band for this algorithm to operate.

   For Block Cipher CID Routing, this consists of the server Server ID, Server
   ID field. Length, Key, and Zero-Padding Length.  The Server ID field indicates the encoding that represents is unique to
   each server, but the
   destination server.

7.4.9.  RETRY_SERVICE_STATELESS message others MUST be global.

   A no-shared-state retry service uses this message (type=0x08) to
   notify full QUIC-LB configuration MUST also specify the server information
   content of the existence first CID octet and the presence and mode of this service.  This message has
   no fields.

7.4.10.  RETRY_SERVICE_STATEFUL message

   A shared-state retry service uses this message (type=0x09) any Retry
   Service.

   The following pseudocode depicts the data items necessary to tell store a
   full QUIC-LB configuration at the server about its existence, server.  It is meant to describe
   the conceptual range and share not specify the key needed to decrypt
   server-generated retry tokens.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                           Key (128)                           +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

8. presentation of such
   configuration in an internet packet.  The comments signify the range
   of acceptable values where applicable.

   uint2    config_rotation_bits;
   enum     { in_band_config, out_of_band_config } config_method;
   select (config_method) {
       case in_band_config: uint64 config_token;
       case out_of_band_config: null;
   } config-method
   boolean  first_octet_encodes_cid_length;
   enum     { none, non_shared_state, shared_state } retry_service;
   select (retry_service) {
       case none: null;
       case non_shared_state: null;
       case shared_state: uint8 key[16];
   } retry_service_config;
   enum     { none, plaintext, obfuscated, stream_cipher, block_cipher }
                     routing_algorithm;
   select (routing_algorithm) {
       case none: null;
       case plaintext: struct {
           uint8 server_id_length; /* 1..19 */
           uint8 server_id[server_id_length];
       } plaintext_config;
       case obfuscated: struct {
           uint8  routing_bit_mask[19];
           uint16 divisor; /* Must be odd */
           uint16 modulus; /* 0..(divisor - 1) */
       } obfuscated_config;
       case stream_cipher: struct {
           uint8  nonce_length; /* 8..16 */
           uint8  server_id_length; /* 1..(19 - nonce_length) */
           uint8  server_id[server_id_length];
           uint8  key[16];
       } stream_cipher_config;
       case block_cipher: struct {
           uint8  server_id_length;
           uint8  zero_padding_length; /* 0..(16 - server_id_length) */
           uint8  server_id[server_id_length];
           uint8  key[16];
       } block_cipher_config;
  } routing_algorithm_config;

7.  Security Considerations

   QUIC-LB is intended to preserve routability and prevent linkability.  Attacks on the protocol would compromise at least one of these
   objectives. therefore
   attempt to subvert this purpose.

   Note that the Plaintext CID algorithm makes no attempt to obscure the
   server mapping, and therefore does not address these concerns.  It
   exists to allow consistent CID encoding for compatibility across a
   network infrastructure.  Servers that are running the Plaintext CID
   algorithm SHOULD only use it to generate new CIDs for the Server
   Initial Packet and SHOULD NOT send CIDs in QUIC NEW_CONNECTION_ID
   frames.  Doing so might falsely suggest to the client that said CIDs
   were generated in a secure fashion.

   A routability attack would inject QUIC-LB messages so that load
   balancers incorrectly route QUIC connections.

   A linkability attack would find some means of determining that two
   connection IDs route to the same server.  As described above, there
   is no scheme that strictly prevents linkability for all traffic
   patterns, and therefore efforts to frustrate any analysis of server
   ID encoding have diminishing returns.

8.1.  Outside attackers

   For an outside

7.1.  Attackers not between the load balancer and server

   Any attacker might open a connection to break routability, it must inject packets
   that correctly guess the 64-bit token, server infrastructure and servers must be reachable
   from these outside hosts.  Load balancers SHOULD drop QUIC-LB packets
   that arrive on its external interface.

   Off-path outside attackers cannot observe
   aggressively retire connection IDs, and will
   therefore struggle to link them.

   On-path outside attackers might try IDs to link connection obtain a large sample of IDs
   that map to the same QUIC connection. server.  It could then apply analytical
   techniques to try to obtain the server encoding.

   The Encrypted CID algorithm provides robust entropy to making any
   sort of linkage.  The Obfuscated CID obscures the mapping and
   prevents trivial brute-force attacks to determine the routing
   parameters, but does not provide robust protection against
   sophisticated attacks.

8.2.  Inside Attackers

   As described above,

   Were this analysis to obtain the server encoding, then on-path inside attackers
   observers might apply this analysis to correlating different client
   IP addresses.

7.2.  Attackers between the load balancer and server

   Attackers in this privileged position are intrinsically able to map
   two connection IDs to the same server.  The QUIC-LB algorithms do
   prevent the linkage of two connection IDs to the same individual
   connection if servers make reasonable selections when generating new
   IDs for that connection.

   On-path inside attackers can break routability for new and migrating
   connections by copying the token from QUIC-LB messages.  From this
   privileged position, however, there are many other attacks that can
   break QUIC connections to the server during the handshake.

   Off-path inside attackers cannot observe connection IDs to link them.
   To successfully break routability, they must correctly guess the
   token.

9.

8.  IANA Considerations

   There are no IANA requirements.

10.

9.  References
10.1.

9.1.  Normative References

   [QUIC-TRANSPORT]
              Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", draft-ietf-quic-
              transport (work in progress).

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <https://www.rfc-editor.org/info/rfc3339>.

10.2.

9.2.  Informative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

Appendix A.  Acknowledgments

Appendix B.  Change Log

      *RFC Editor's Note:* Please remove this section prior to
      publication of a final version of this document.

B.1.  since-draft-ietf-quic-load-balancers-00

   o  Removed in-band protocol from the document

B.2.  Since draft-duke-quic-load-balancers-06

   o  Switch to IETF WG draft.

B.2.

B.3.  Since draft-duke-quic-load-balancers-05

   o  Editorial changes

   o  Made load balancer behavior independent of QUIC version

   o  Got rid of token in stream cipher encoding, because server might
      not have it

   o  Defined "non-compliant DCID" and specified rules for handling
      them.

   o  Added psuedocode for config schema

B.3.

B.4.  Since draft-duke-quic-load-balancers-04

   o  Added standard for retry services

B.4.

B.5.  Since draft-duke-quic-load-balancers-03

   o  Renamed Plaintext CID algorithm as Obfuscated CID

   o  Added new Plaintext CID algorithm

   o  Updated to allow 20B CIDs

   o  Added self-encoding of CID length

B.5.

B.6.  Since draft-duke-quic-load-balancers-02

   o  Added Config Rotation

   o  Added failover mode

   o  Tweaks to existing CID algorithms

   o  Added Block Cipher CID algorithm

   o  Reformatted QUIC-LB packets

B.6.

B.7.  Since draft-duke-quic-load-balancers-01

   o  Complete rewrite

   o  Supports multiple security levels

   o  Lightweight messages

B.7.

B.8.  Since draft-duke-quic-load-balancers-00

   o  Converted to markdown

   o  Added variable length connection IDs

Authors' Addresses

   Martin Duke
   F5 Networks, Inc.

   Email: martin.h.duke@gmail.com
   Nick Banks
   Microsoft

   Email: nibanks@microsoft.com