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QUIC                                                             M. Duke
Internet-Draft                                         F5 Networks, Inc.
Intended status: Standards Track                      September 17, 2018
Expires: March 21, 2019


            QUIC-LB: Generating Routable QUIC Connection IDs
                    draft-duke-quic-load-balancers-02

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 of that
   encoding.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 21, 2019.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Protocol Objectives . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Simplicity  . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Security  . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Robustness to Middleboxes . . . . . . . . . . . . . . . .   5
     2.4.  Load Balancer Chains  . . . . . . . . . . . . . . . . . .   5
   3.  Routing Algorithms  . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Plaintext CID Algorithm . . . . . . . . . . . . . . . . .   6
       3.1.1.  Load Balancer Actions . . . . . . . . . . . . . . . .   6
       3.1.2.  Server Actions  . . . . . . . . . . . . . . . . . . .   6
     3.2.  Encrypted CID Algorithm . . . . . . . . . . . . . . . . .   7
       3.2.1.  Load Balancer Actions . . . . . . . . . . . . . . . .   7
       3.2.2.  Server Actions  . . . . . . . . . . . . . . . . . . .   8
   4.  Protocol Description  . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Out of band sharing . . . . . . . . . . . . . . . . . . .   8
     4.2.  QUIC-LB Message Exchange  . . . . . . . . . . . . . . . .   8
       4.2.1.  Packet Header Format  . . . . . . . . . . . . . . . .   9
       4.2.2.  Ack Payload . . . . . . . . . . . . . . . . . . . . .   9
       4.2.3.  Fail Payload  . . . . . . . . . . . . . . . . . . . .  10
       4.2.4.  Routing Info Payload  . . . . . . . . . . . . . . . .  11
       4.2.5.  Encrypted CID Payload . . . . . . . . . . . . . . . .  11
       4.2.6.  Server ID Payload . . . . . . . . . . . . . . . . . .  12
       4.2.7.  Modulus Payload . . . . . . . . . . . . . . . . . . .  13
   5.  Configuration Requirements  . . . . . . . . . . . . . . . . .  13
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
     6.1.  Outside attackers . . . . . . . . . . . . . . . . . . . .  14
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  15
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  15
   Appendix B.  Change Log . . . . . . . . . . . . . . . . . . . . .  15
     B.1.  Since draft-duke-quic-load-balancers-00 . . . . . . . . .  15
     B.2.  Since draft-duke-quic-load-balancers-01 . . . . . . . . .  15
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  16








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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 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.

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.




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   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



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   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.

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 encoding routing information for each load balancer,
   this use case is out of scope for QUIC-LB.

3.  Routing Algorithms

   In QUIC-LB, load balancers do not send 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.

   The load balancer SHOULD route Initial and 0-RTT packets from the
   client using an alternate algorithm.  Note that the SCID in these
   packets may not be long enough to represent all the routing bits.
   This algorithm SHOULD generate consistent results for Initial and
   0RTT packets that arrive with the same source and destination




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   connection ID.  The load balancer algorithms below apply to all
   incoming Handshake and 1-RTT packets.

3.1.  Plaintext CID Algorithm

3.1.1.  Load Balancer Actions

   The load balancer selects an arbitrary set of 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 load balancer selects a divisor that MUST be larger than the
   number of servers.  It SHOULD be large enough to accommodate
   reasonable increases in the number of servers.

   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.

   The load balancer shares these three values with servers, as
   explained in Section 4.

   Upon receipt of a QUIC packet that is not of type Initial or 0-RTT,
   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 the destination server.  .
   Note that any SCID that contains a server's modulus, plus an
   arbitrary integer multiple of the divisor, in the routing bits is
   routable to that server regardless of the contents of the non-routing
   bits.  Outside observers that do not know the divisor or the routing
   bits will therefore have difficulty identifying that two SCIDs route
   to the same server.

   Note also that not all Connection IDs are necessarily routable, as
   the computed modulus may not match one assigned to any server.  Load
   balancers SHOULD drop these packets if not a QUIC Initial or 0-RTT
   packet.

3.1.2.  Server Actions

   The server may choose any connection ID length that can represent all
   of the routing bits.





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   When a server needs a new connection ID, it adds an arbitrary
   nonnegative integer multiple of the divisor 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 the result in the routing bits.  It MAY put any
   other value into the non-routing bits.  The non-routing bits SHOULD
   appear random to observers.

3.2.  Encrypted CID Algorithm

   The Encrypted CID algorithm provides true cryptographic protection,
   rather than mere obfuscation, at the cost of additional per-packet
   processing at the load balancer to decrypt every incoming connection
   ID except for Initial and 0RTT packets.

3.2.1.  Load Balancer Actions

   The load balancer assigns a server ID to every server in its pool,
   and determines a server ID length (in octets) sufficiently large to
   encode all server IDs, including potential future servers.  The
   server ID will be encoded in the first octets of the connection ID.

   The load balancer also selects a connection ID length that all
   servers must use, and an 16-octet AES-CTR key to use for connection
   ID decryption.

   The load balancer shares these three values with servers, as
   explained in Section 4.

   Upon receipt of a QUIC packet that is not of type Initial or 0-RTT,
   the load balancer extracts as many of the earliest octets from the
   destination connection ID as necessary to match the server ID length.

   The load balancer decrypts the server ID using 128-bit AES in counter
   (CTR) mode, much like QUIC packet number decryption.  The counter
   input to AES-CTR is the bytes of the connection ID that do not
   constitute the encrypted server ID.

   server_id = AES-CTR(key, non-server-id-bytes, encrypted_server_id)

   The output of the decryption is the server ID that the load balancer
   uses for routing.







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3.2.2.  Server Actions

   When generating a routable connection ID, the server writes its
   provided server ID into the server ID octets, and arbitrary bits into
   the remaining required connection ID octets.  These arbitrary bits
   MAY encode additional information, but SHOULD appear essentially
   random to observers.

   The server then encrypts the server ID bytes using 128-bit AES in
   counter (CTR) mode, much like QUIC packet number encryption.  The
   counter input to AES-CTR is the bytes of the connection ID that do
   not constitute the encrypted server ID.

   encrypted_server_id = AES-CTR(key, non_server_id_bytes, server-id)

4.  Protocol Description

   The fundamental protocol requirement is to share the choice of
   routing algorithm, and the relevant parameters for that algorithm,
   between load balancer and server.

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

   For Encrypted CID Routing, this consists of the Server ID, Server ID
   Length, Key, and Connection ID Length.  The Server ID is unique to
   each server, but the others MUST be global.

4.1.  Out of band sharing

   When there are concerns about the integrity of the path between load
   balancer 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 be shared out-
   of-band, while the load balancer sends the unique server IDs via the
   truncated message formats presented below.

4.2.  QUIC-LB Message Exchange

   QUIC-LB load balancers send the encoding parameters to servers as
   they discover the servers, using a single packet to each that
   resembles QUIC.  They periodically retransmit this packet to each
   server until that server responds with a QUIC-LB ack.  Specifics of
   this retransmission are implementation-dependent.




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   These message formats are specific to QUICv2 and experimental
   versions leading up to QUICv2.  They may require revision for future
   versions of QUIC.

4.2.1.  Packet Header Format

    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
   +-+-+-+-+-+-+-+-+
   | Type = 0xfb   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Version (32)                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      0x00     |
   +-+-+-+-+-+-+-+-+

                         Figure 1: QUIC-LB Header

   QUIC-LB messages are QUIC packets with a long header and zero length
   connection IDs.  They are sent when a load balancer boots up, or
   detects a new server in the pool.  QUIC-LB packets are delivered in a
   UDP datagram.

   The type field is 0xfb, which is otherwise unused in QUICv2.

   The Version field allows QUIC-LB to use the Version Negotiation
   mechanism.  All messages in this specification are specific to
   QUICv2, as future QUIC versions may use the 0xfb packet type for
   other purposes.  Therefore, the Version field should be set as the
   codepoint for QUICv2 as defined in [QUIC-TRANSPORT].

   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 the version.

   The 0x00 byte indicates that there are no connection IDs present in
   the header.

   The remainder of the packet is the payload.  This has multiple
   formats.

4.2.2.  Ack Payload









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    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Type = 0x00  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                            Token (64)                         +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           Figure 2: Ack Payload

   The Ack Payload consists of nine octets.  Servers send this payload
   after receipt of any acceptable QUIC-LB packet from a load balancer.

   The token field echoes the token field from the acknowledged packet.

   Load balancers MUST retransmit a QUIC-LB packet if not followed by a
   valid Ack Payload or Version Negotiation Packet from the destination
   after a reasonable interval.

4.2.3.  Fail Payload

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Type = 0x01  |   Supp. Type  |  Supp. Type   |  ...
   +-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                            Token (64)                         +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                          Figure 3: Fail Payload

   Servers MUST send a Fail Payload upon receipt of a payload type which
   they do not support, or if they do not possess all of the implied
   out-of-band configuration to support a particular payload type.

   After the type octet, servers append additional octets to list all
   payload types they support.

   The token field echoes the token field from the acknowledged packet.

   Upon receipt of a Fail Payload, Load Balancers MUST either send a
   QUIC-LB payload the server supports, or remove the server from the
   server pool.




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4.2.4.  Routing Info Payload

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Type = 0x02  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                            Token (64)                         +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                       Routing Bit Mask (144)                  +
   |                                                               |
   +                                                               +
   |                                                               |
   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |         Modulus (16)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Divisor (16)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 4: Routing Info Payload

   The Type Octet indicates that this is a Routing Info Payload, which
   contains all parameters for the plaintext CID algorithm.

   The Token is an 8-octet field that both entities obtain at
   configuration time.  It is used to verify that the sender is not an
   inside off-path attacker.  Servers SHOULD silently drop QUIC-LB
   packets with an incorrect token.

   The Routing Bit Mask encodes a '1' at every bit position in the
   server connection ID that will encode routing information.

   These bits, along with the Modulus and Divisor, are chosen by the
   load balancer as described in Section 3.1.

4.2.5.  Encrypted CID Payload










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    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Type = 0x03  |   CIDL (8)    |    SIDL (8)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                            Token (64)                         +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Server ID (variable)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                             Key (128)                         +
   |                                                               |
   +                                                               +
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 5: Encrypted CID Payload

   The CIDL field is a one-octet unsigned integer that describes the
   server connection ID length necessary to use this routing algorithm,
   in octets.

   The SIDL field is a one-octet unsigned integer that describes the
   server ID length necessary to use this routing algorithm, in octets.

   The server ID is the unique value assigned to the receiving server.
   Its length is determined by the SIDL field.

   The key is an 16-octet field that contains the key that the load
   balancer will use to decrypt server IDs on QUIC packets.  See
   Section 6 to understand why sending keys in plaintext may be a safe
   strategy.

4.2.6.  Server ID Payload

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Type = 0x04  |    SIDL (8)   |       Server ID (variable)    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                            Token (64)                         +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 6: Server ID Payload




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   Load balancers send the Server ID when all global values for CID
   encryption are sent out-of-band, so that only the server-unique
   values must be sent in-band.  The fields are identical to their
   counterparts in the Encrypted CID payload.

4.2.7.  Modulus Payload

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Type = 0x05  |           Modulus (16)        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                            Token (64)                         +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 7: Modulus Payload

   Load balancers send the Modulus when all global values for Plaintext
   CIDs are sent out-of-band, so that only the server- unique values
   must be sent in-band.  The Modulus field is identical to its
   counterpart in the Routing Info payload.

5.  Configuration Requirements

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

   There are three levels of configuration that correspond to increasing
   levels of concern about the security of the load balancer-server
   path.

   The complete information requirements are described in Section 4.
   Load balancers MUST have configuration for all parameters of each
   routing algorithm they support.

   If there is any in-band communication, servers MUST be explicitly
   configured with the token of the load balancer they expect to
   interface with.

   Optionally, servers MAY be configured with the global parameters of
   supported routing algorithms.  This allows load balancers to use
   Server ID and Modulus Payloads, limiting the information sent in-
   band.




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   Finally, servers MAY be directly configured with their unique server
   IDs or modulus, eliminating need for in-band messaging at all.  In
   this case, servers and load balancers MUST enable only one routing
   algorithm, as there is no explicit message to agree on one or the
   other.

6.  Security Considerations

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

   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.

6.1.  Outside attackers

   For an outside attacker to break routability, it must inject packets
   that correctly guess the 64-bit token, 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 connection IDs, and will
   therefore struggle to link them.

   On-path outside attackers might try to link connection IDs to the
   same QUIC connection.  The Encrypted CID algorithm provides robust
   entropy to making any sort of linkage.  The Plaintext CID obscures
   the mapping and prevents trivial brute-force attacks to determine the
   routing parameters, but does not provide robust protection against
   sophisticated attacks.

   ## Inside Attackers

   As described above, on-path inside attackers 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



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   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.

7.  IANA Considerations

   There are no IANA requirements.

8.  References

8.1.  Normative References

   [QUIC-TRANSPORT]
              Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", draft-ietf-quic-
              transport-14 (work in progress).

8.2.  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-duke-quic-load-balancers-00

   o  Converted to markdown

   o  Added variable length connection IDs

B.2.  Since draft-duke-quic-load-balancers-01

   o  Complete rewrite

   o  Supports multiple security levels

   o  Lightweight messages




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Author's Address

   Martin Duke
   F5 Networks, Inc.

   Email: martin.h.duke@gmail.com













































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