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Network Working Group D. Farinacci
Internet-Draft V. Fuller
Intended status: Experimental D. Oran
Expires: February 14, 2008 D. Meyer
cisco Systems
August 13, 2007
Locator/ID Separation Protocol (LISP)
draft-farinacci-lisp-03.txt
Status of this Memo
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This Internet-Draft will expire on February 14, 2008.
Copyright Notice
Copyright (C) The IETF Trust (2007).
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Abstract
This draft describes a simple, incremental, network-based protocol to
implement separation of Internet addresses into Endpoint Identifiers
(EIDs) and Routing Locators (RLOCs). This mechanism requires no
changes to host stacks and no major changes to existing database
infrastructures. The proposed protocol can be implemented in a
relatively small number of routers.
This proposal was stimulated by the problem statement effort at the
Amsterdam IAB Routing and Addressing Workshop (RAWS), which took
place in October 2006.
Table of Contents
1. Requirements Notation . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 6
4. Basic Overview . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1. Packet Flow Sequence . . . . . . . . . . . . . . . . . . . 10
5. Tunneling Details . . . . . . . . . . . . . . . . . . . . . . 13
5.1. LISP IPv4-in-IPv4 Header Format . . . . . . . . . . . . . 14
5.2. LISP IPv6-in-IPv6 Header Format . . . . . . . . . . . . . 15
5.3. Tunnel Header Field Descriptions . . . . . . . . . . . . . 16
6. EID-to-RLOC Mapping . . . . . . . . . . . . . . . . . . . . . 18
6.1. Control-Plane Packet Format . . . . . . . . . . . . . . . 18
6.1.1. Map-Request Message Format . . . . . . . . . . . . . . 20
6.1.2. EID-to-RLOC UDP Map-Request Message . . . . . . . . . 21
6.1.3. Map-Reply Message Format . . . . . . . . . . . . . . . 22
6.1.4. EID-to-RLOC UDP Map-Reply Message . . . . . . . . . . 24
6.2. Routing Locator Selection . . . . . . . . . . . . . . . . 24
6.3. Routing Locator Reachability . . . . . . . . . . . . . . . 26
7. Router Performance Considerations . . . . . . . . . . . . . . 28
8. Deployment Scenarios . . . . . . . . . . . . . . . . . . . . . 29
8.1. First-hop/Last-hop Tunnel Routers . . . . . . . . . . . . 30
8.2. Border/Edge Tunnel Routers . . . . . . . . . . . . . . . . 30
8.3. ISP Provider-Edge (PE) Tunnel Routers . . . . . . . . . . 31
9. Multicast Considerations . . . . . . . . . . . . . . . . . . . 32
10. Security Considerations . . . . . . . . . . . . . . . . . . . 33
11. Prototype Plans and Status . . . . . . . . . . . . . . . . . . 34
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 36
12.1. Normative References . . . . . . . . . . . . . . . . . . . 36
12.2. Informative References . . . . . . . . . . . . . . . . . . 36
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 39
Intellectual Property and Copyright Statements . . . . . . . . . . 40
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1. Requirements Notation
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 [RFC2119].
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2. Introduction
Many years of discussion about the current IP routing and addressing
architecture have noted that its use of a single numbering space (the
"IP address") for both host transport session identification and
network routing creates scaling issues (see [CHIAPPA] and [RFC1498]).
A number of scaling benefits would be realized by separating the
current IP address into separate spaces for Endpoint Identifiers
(EIDs) and Routing Locators (RLOCs); among them are:
1. Reduction of routing table size in the "default-free zone" (DFZ).
Use of a separate numbering space for RLOCs will allow them to be
assigned topologically (in today's Internet, RLOCs would be
assigned by providers at client network attachment points),
greatly improving aggregation and reducing the number of
globally-visible, routable prefixes.
2. Easing of renumbering burden when clients change providers.
Because host EIDs are numbered from a separate, non-provider-
assigned and non-topologically-bound space, they do not need to
be renumbered when a client site changes its attachment points to
the network.
3. Mobility with session survivability. Because session state is
associated with a persistent host EID, it should be possible for
a host (or a collection of hosts) to move to a different point in
the network topology (whether by changing providers or by
physically moving) without disruption of connectivity.
4. Traffic engineering capabilities that can be performed by network
elements and do not depend on injecting additional state into the
routing system. This will fall out of the mechanism that is used
to implement the EID/RLOC split (see Section 4).
This draft describes protocol mechanisms to achieve the desired
functional separation. For flexibility, the document decouples the
mechanism used for forwarding packets from that used to determine EID
to RLOC mappings. This work is in response to and intended to
address the problem statement that came out of the RAWS effort
[RAWS].
This draft focuses on a router-based solution. Building the solution
into the network should facilitate incremental deployment of the
technology on the Internet. Note that while the detailed protocol
specification and examples in this document assume IP version 4
(IPv4), there is nothing in the design that precludes use of the same
techniques and mechanisms for IPv6. It should be possible for IPv4
packets to use IPv6 RLOCs and for IPv6 EIDs to be mapped to IPv4
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RLOCs.
Related work on host-based solutions is described in Shim6 [SHIM6]
and HIP [RFC4423]. Related work on other router-based solutons is
described in GSE [GSE]. This draft attempts to not compete or
overlap with such solutions and the proposed protocol changes are
expected to complement a host-based mechanism when Traffic
Engineering functionality is desired.
Some of the design goals of this proposal include:
1. Minimize required changes to Internet infrastructure.
2. Require no hardware or software changes to end-systems (hosts).
3. Be incrementally deployable.
4. Require no router hardware changes.
5. Minimize router software changes.
6. Avoid or minimize packet loss when EID-to-RLOC mappings need to
be performed.
There are 4 variants of LISP, which differ along a spectrum of strong
to weak dependence on the topological nature and possible need for
routability of EIDs. The variants are:
LISP 1: where EIDs are routable through the RLOC topology for
bootstrapping EID-to-RLOC mappings. [LISP1]
LISP 1.5: where EIDs are routable for bootstrapping EID-to-RLOC
mappings; such routing is via a separate topology.
LISP 2: where EIDS are not routable and EID-to-RLOC mappings are
implemented within the DNS. [LISP2]
LISP 3: where non-routable EIDs are used as lookup keys for a new
EID-to-RLOC mapping database. Use of Distributed Hash Tables
[DHTs] to implement such a database would be an area to explore.
Other examples of new mapping database services are [CONS],
[RPMD], [NERD], and [APT].
This document will focus on LISP 1 and LISP 1.5, both of which rely
on a router-based distributed cache and database for EID-to-RLOC
mappings. The LISP 2 and LISP 3 mechanisms, which require separate
EID-to-RLOC infrastructure, will be documented in additional drafts.
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3. Definition of Terms
Provider Independent (PI) Addresses: an address block assigned from
a pool that is not associated with any service provider and is
therefore not topologically-aggregatable in the routing system.
Provider Assigned (PA) Addresses: a block of IP addresses that are
assigned to a site by each service provider to which a site
connects. Typically, each block is sub-block of a service
provider CIDR block and is aggregated into the larger block before
being advertised into the global Internet. Traditionally, IP
multihoming has been implemented by each multi-homed site
acquiring its own, globally-visible prefix. LISP uses only
topologically-assigned and aggregatable address blocks for RLOCs,
eliminating this demonstrably non-scalable practice.
Routing Locator (RLOC): the IPv4 or IPv6 address of an egress
tunnel router (ETR). It is the output of a EID-to-RLOC mapping
lookup. An EID maps to one or more RLOCs. Typically, RLOCs are
numbered from topologically-aggregatable blocks that are assigned
to a site at each point to which it attaches to the global
Internet; where the topology is defined by the connectivity of
provider networks, RLOCs can be thought of as PA addresses.
Multiple RLOCs can be assigned to the same ETR device or to
multiple ETR devices at a site.
Endpoint ID (EID): a 32- or 128-bit value used in the source and
destination address fields of the first (most inner) LISP header
of a packet. The host obtains a destination EID the same way it
obtains an destination address today, for example through a DNS
lookup or SIP exchange. The source EID is obtained via existing
mechanisms used to set a hosts "local" IP address. An EID is
allocated to a host from an EID-prefix block associated with the
site the host is attached to. An EID can be used by a host to
refer to other hosts. LISP uses PI blocks for EIDs; such EIDs
MUST NOT be used as LISP RLOCs. Note that EID blocks may be
assigned in a hierarchical manner, independent of the network
topology, to facilitate scaling of the mapping database. In
addition, an EID block assigned to a site may have site-local
structure (subnetting) for routing within the site; this structure
is not visible to the global routing system.
EID-prefix: A power-of-2 block of EIDs which are allocated to a
site by an address allocation authority. EID-prefixes are
associated with a set of RLOC addresses which make up a "database
mapping". EID-prefix allocations can be broken up into smaller
blocks when an RLOC set is to be associated with the smaller EID-
prefix.
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End-system: is an IPv4 or IPv6 device that originates packets with
a single IPv4 or IPv6 header. The end-system supplies an EID
value for the destination address field of the IP header when
communicating globally (i.e. outside of it's routing domain). An
end-system can be a host computer, a switch or router device, or
any network appliance. An iPhone.
Ingress Tunnel Router (ITR): a router which accepts an IP packet
with a single IP header (more precisely, an IP packet that does
not contain a LISP header). The router treats this "inner" IP
destination address as an EID and performs an EID-to-RLOC mapping
lookup. The router then prepends an "outer" IP header with one of
its globally-routable RLOCs in the source address field and the
result of the mapping lookup in the destination address field.
Note that this destination RLOC may be an intermediate, proxy
device that has better knowledge of the EID-to-RLOC mapping
closest to the destination EID. In general, an ITR receives IP
packets from site end-systems on one side and sends LISP-
encapsulated IP packets toward the Internet on the other side.
Specifically, when a service provider prepends a LISP header for
Traffic Engineering purposes, the router that does this is also
regarded as an ITR. The outer RLOC the ISP ITR uses can be based
on the outer destination address (the originating ITR's supplied
RLOC) or the inner destination address (the originating hosts
supplied EID).
TE-ITR: is an ITR that is deployed in a service provider network
that prepends an additional LISP header for Traffic Engineering
purposes.
Egress Tunnel Router (ETR): a router that accepts an IP packet
where destination address in the "outer" IP header is one of its
own RLOCs. The router strips the "outer" header and forwards the
packet based on the next IP header found. In general, an ETR
receives LISP-encapsulated IP packets from the Internet on one
side and sends decapsulated IP packets to site end-systems on the
other side. ETR functionality does not have to be limited to a
router device. A server host can be the endpoint of a LISP tunnel
as well.
TE-ETR: is an ETR that is deployed in a service provider network
that strips an outer LISP header for Traffic Engineering purposes.
EID-to-RLOC Cache: a short-lived, on-demand database in an ITR that
stores, tracks, and is responsible for timing-out and otherwise
validating EID-to-RLOC mappings. This cache is distinct from the
"database", the cache is dynamic, local, and relatively small
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while and the database is distributed, relatively static, and much
global in scope.
EID-to-RLOC Database: a globally, distributed database that
contains all known EID-prefix to RLOC mappings. Each potential
ETR typically contains a small piece of the database: the EID-to-
RLOC mappings for the EID prefixes "behind" the router. These map
to one of the router's own, globally-visible, IP addresses.
Recursive Tunneling: when a packet has more than one LISP IP
header. Additional layers of tunneling may be employed to
implement traffic engineering or other re-routing as needed. When
this is done, an additional "outer" LISP header is added and the
original RLOCs are preserved in the "inner" header.
Reencapsulating Tunnels: when a packet has no more than one LISP IP
header (two IP headers total) and when it needs to be diverted to
new RLOC, an ETR can decapsulate the packet (remove the LISP
header) and prepend a new tunnel header, with new RLOC, on to the
packet. Doing this allows a packet to be re-routed by the re-
encapsulating router without adding the overhead of additional
tunnel headers.
LISP Header: a term used in this document to refer to the outer
IPv4 or IPv6 header, a UDP header, and a LISP header, an ITR
prepends or an ETR strips.
Address Family Indicator (AFI): a term used to describe an address
encoding in a packet. An address family currently pertains to an
IPv4 or IPv6 address. See [AFI] for details.
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4. Basic Overview
One key concept of LISP is that end-systems (hosts) operate the same
way they do today. The IP addresses that hosts use for tracking
sockets, connections, and for sending and receiving packets do not
change. In LISP terminology, these IP addresses are called Endpoint
Identifiers (EIDs).
Routers continue to forward packets based on IP destination
addresses. These addresses are referred to as Routing Locators
(RLOCs). Most routers along a path between two hosts will not
change; they continue to perform routing/forwarding lookups on
addresses (RLOCs) in the IP header.
This design introduces "Tunnel Routers", which prepend LISP headers
on host-originated packets and strip them prior to final delivery to
their destination. The IP addresses in this "outer header" are
RLOCs. During end-to-end packet exchange between two Internet hosts,
an ITR prepends a new LISP header to each packet and an egress tunnel
router strips the new header. The ITR performs EID-to-RLOC lookups
to determine the routing path to the the ETR, which has the RLOC as
one of its IP addresses.
Some basic rules governing LISP are:
o End-systems (hosts) only know about EIDs.
o EIDs are always IP addresses assigned to hosts.
o Routers mostly deal with Routing Locator addresses. See details
later in Section 4.1 to clarify what is meant by "mostly".
o RLOCs are always IP addresses assigned to routers; preferably,
topologically-oriented addresses from provider CIDR blocks.
o Routers can use their RLOCs as EIDs but can also be assigned EIDs
when performing host functions. Those EIDs MUST NOT be used as
RLOCs. When EIDs are used the routeability of them is scoped to
within the site. A hybrid use of this, for example is when a
router runs the BGP protocol where iBGP peerings may use EIDs and
eBGP peerings may use RLOCs.
o EIDs are not expected to be usable for global end-to-end
communication in the absence of an EID-to-RLOC mapping operation.
They are expected to be used locally for intra-site communication.
o EID prefixes are likely to be hierarchically assigned in a manner
which is optimized for administrative convenience and to
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facilitate scaling of the EID-to-RLOC mapping database. The
hierarchy is based on a address alocation hierarchy which is not
dependent on the network toplogy.
o EIDs may also be structured (subnetted) in a manner suitable for
local routing within an autonomous system.
An additional LISP header may be pre-pended to packets by a transit
router (i.e. TE-ITR) when re-routing of the end-to-end path for a
packet is desired. An obvious instance of this would be an ISP
router that needs to perform traffic engineering for packets in flow
through its network. In such a situation, termed Recursive
Tunneling, an ISP transit acts as an additional ingress tunnel router
and the RLOC it uses for the new prepended header would be either an
TE-ETR within the ISP (along intra-ISP traffic engineered path) or in
an TE-ETR within another ISP (an inter-ISP traffic engineered path,
where an agreement to build such a path exists).
Tunnel Routers can be placed fairly flexibly in a multi-AS topology.
For example, the ITR for a particular end-to-end packet exchange
might be the first-hop or default router within a site for the source
host. Similarly, the egress tunnel router might be the last-hop
router directly-connected to the destination host. Another example,
perhaps for a VPN service out-sourced to an ISP by a site, the ITR
could be the site's border router at the service provider attachment
point. Mixing and matching of site-operated, ISP-operated, and other
tunnel routers is allowed for maximum flexibility. See Section 8 for
more details.
4.1. Packet Flow Sequence
This section provides an example of the unicast packet flow with the
following parameters:
o Source host "host1.abc.com" is sending a packet to
"host2.xyz.com".
o Each site is multi-homed, so each tunnel router has an address
(RLOC) assigned from each of the site's attached service provider
address blocks.
o The ITR and ETR are directly connected to the source and
destination, respectively.
Client host1.abc.com wants to communicate with server host2.xyz.com:
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1. host1.abc.com wants to open a TCP connection to host2.xyz.com.
It does a DNS lookup on host2.xyz.com. An A/AAAA record is
returned. This address is used as the destination EID and the
locally-assigned address of host1.abc.com is used as the source
EID. An IP/IPv6 packet is built using the EIDs in the IP/IPv6
header and sent to the default router.
2. The default router is configured as an ITR. It prepends a LISP
header to the packet, with one of its RLOCs as the source IP/IPv6
address and uses the destination EID from the original packet
header as the destination IP/IPv6 address. Subsequent packets
continue to behave the same way until a mapping is learned.
3. In LISP 1, the packet is routed through the Internet as it is
today. In LISP 1.5, the packet is routed on a different topology
which may have EID prefixes distributed and advertised in an
aggregatable fashion. In either case, the packet arrives at the
ETR. The router is configured to "punt" the packet to the
router's control-plane processor. See Section 7 for more
details.
4. The LISP header is stripped so that the packet can be forwarded
by the router control-plane. The router looks up the destination
EID in the router's EID-to-RLOC database (not the cache, but the
configured data structure of RLOCs). An EID-to-RLOC Map-Reply
message is originated by the egress router and is addressed to
the source RLOC from the LISP header of the original packet (this
is the ITR). The source RLOC in the IP header of the UDP message
is one of the ETR's RLOCs (one of the RLOCs that is embedded in
the UDP payload).
5. The ITR receives the UDP message, parses the message (to check
for format validity) and stores the EID-to-RLOC information from
the packet. This information is put in the ITR's EID-to-RLOC
mapping cache (this is the on-demand cache, the cache where
entries time out due to inactivity).
6. Subsequent packets from host1.abc.com to host2.xyz.com will have
a LISP header prepended with the RLOCs learned from the ETR.
7. The egress tunnel receives these packets directly (since the
destination address is one of its assigned IP addresses), strips
the LISP header and delivers the packets to the attached
destination host.
In order to eliminate the need for a mapping lookup in the reverse
direction, the ETR gleans RLOC information from the LISP header.
Both ITR and the ETR may also influence the decision the other makes
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in selecting an RLOC. See Section 6 for more details.
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5. Tunneling Details
This section describes the LISP Data Message which defines the
tunneling header used to encapsulate IPv4 and IPv6 packets which
contain EID addresses. Even though the following formats illustrate
IPv4-in-IPv4 and IPv6-in-IPv6 encapsulations, the other 2
combinations are supported as well.
Since additional tunnel headers are prepended, the packet becomes
larger and in theory can exceed the MTU of any link traversed from
the ITR to the ETR. It is recommended, in IPv4 that packets do not
get fragmented as they are encapsulated by the ITR. Instead, the
packet is dropped and an ICMP Too Big message is returned to the
source.
In practice, this is not really a problem. Hosts typically do not
originate IP packets larger than 1500 bytes. And second, a survey
has been taken (from a list of ISPs, see Acknowledgement section)
where nearly all ISP link MTUs are either 4470 bytes or support
Ethernet jumbo frames of 9000 bytes. Therefore, we don't anticipate
any problems with prepending additional headers.
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5.1. LISP IPv4-in-IPv4 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ |Version| IHL |Type of Service| Total Length |
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Identification |Flags| Fragment Offset |
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OH | Time to Live | Protocol = 17 | Header Checksum |
\ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | Source Routing Locator |
\ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | Destination Routing Locator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Source Port = xxxx | Dest Port = 4342 |
UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | UDP length | UDP Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Type | Locator Reach Bits | Nonce ... |
LISP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | ... Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ |Version| IHL |Type of Service| Total Length |
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Identification |Flags| Fragment Offset |
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IH | Time to Live | Protocol | Header Checksum |
\ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | Source EID |
\ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | Destination EID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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5.2. LISP IPv6-in-IPv6 Header Format
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ |Version| Traffic Class | Flow Label |
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Payload Length | Next Header=17| Hop Limit |
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
O + +
u | |
t + Source Routing Locator +
e | |
r + +
| |
H +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
d | |
r + +
| |
\ + Destination Routing Locator +
\ | |
\ + +
\ | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Source Port = xxxx | Dest Port = 4342 |
UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | UDP length | UDP Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ |Type=1 | Locator Reach Bits | Nonce ... |
LISP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | ... Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ |Version| Traffic Class | Flow Label |
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Payload Length | Next Header | Hop Limit |
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
I + +
n | |
n + Source EID +
e | |
r + +
| |
H +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
d | |
r + +
| |
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\ + Destination EID +
\ | |
\ + +
\ | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.3. Tunnel Header Field Descriptions
IH Header: is the inner header, preserved from the datagram received
from the originating host. The source and destination IP
addresses are EIDs.
OH Header: is the outer header prepended by an ITR. The address
fields contain RLOCs obtained from the ingress router's EID-to-
RLOC cache. The IP protocol number is "UDP (17)" from [RFC0768].
UDP Header: contains a random source port allocated by the ITR when
encapsulating a packet. The destination port MUST be set to the
well-known IANA assigned port value 4342. The UDP checksum field
MUST be transmitted as 0 and not ignore by the ETR.
UDP Length: field contains the original packet's length. For an
IPv4 encapsulated packet, the inner header Total Length is copied.
For an IPv6 encapsualted packet, the inner header Payload Length
plus the size of the IPv6 header (40 bytes) is copied.
LISP Type: set to 1 to encode a LISP Data Message.
LISP Nonce: is an ITR randomly generated 6-byte value which tests
return routability of an ETR echoing back the none in a Map-Reply
message.
LISP Locator Reach Bits: in the LISP header are set by an ITR to
indicate to an ETR the reachability of the Locators in the source
site. Each RLOC in a Map-Reply is assigned an ordinal value from
0 to n-1 (when there are n RLOCs in a mapping entry). The Locator
Reach Bits are number from 0 to n-1 from the right significant bit
of the 12-bit field. When a bit is set to 1, the ITR is
indicating to the ETR the RLOC associated with the bit ordinal is
reachable. See Section 6.3 for details on how an ITR can
determine other site ITRs are reachable.
When doing Recursive Tunneling:
o The OH header Time to Live field (or Hop Limit field, in case of
IPv6) MUST be copied from the IH header Time to Live field.
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o The OH header Type of Service field (or the Traffic Class field,
in the case of IPv6) SHOULD be copied from the IH header Type of
Service field.
When doing Re-encapsulated Tunneling:
o The new OH header Time to Live field SHOULD be copied from the
stripped OH header Time to Live field.
o The new OH header Type of Service field SHOULD be copied from the
stripped OH header Type of Service field.
Copying the TTL serves two purposes. First it preserves the distance
the host intended the packet to travel. And more importantly, it
provides for suppression of looping packets in the event there is a
loop of concatenated tunnels due to misconfiguration.
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6. EID-to-RLOC Mapping
6.1. Control-Plane Packet Format
When LISP 1 or LISP 1.5 are used, new UDP packet types encode the
EID-to-RLOC mappings:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| IHL |Type of Service| Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |Flags| Fragment Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live | Protocol = 17 | Header Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Routing Locator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Routing Locator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Source Port | Dest Port |
UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | UDP length | UDP Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| LISP Message |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Traffic Class | Flow Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Length | Next Header=17| Hop Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Source Routing Locator +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Destination Routing Locator +
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| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Source Port | Dest Port |
UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | UDP length | UDP Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| LISP Message |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The LISP UDP-based messages are the Map-Request and Map-Reply
messages. When a UDP Map-Request is sent, the UDP source port is
chosen by the sender and the destination UDP port number is set to
4342. When a UDP Map-Reply is sent, the source UDP port number is
set to 4342 and the destination UDP port number is copied from the
source port of either the Map-Request of the invoking data packet.
LISP-CONS [CONS] uses TCP with the same message formats. However,
this main LISP specification is the authoritative source for message
format definitions for the Map-Request and Map-Reply messages.
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6.1.1. Map-Request Message Format
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Locator Reach Bits | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... Nonce | Record count |A| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ITR-AFI | CAR-AFI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originating ITR RLOC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originating CAR EID-Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Rec -> | EID mask-len | EID-AFI | EID-prefix ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path Vector List |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Packet field descriptions:
Type: 2 (Map-Request)
Locator Reach Bits: Refer to Section 5.3.
Checksum: A complement of the 1-complements sum of the LISP packet.
The checksum MUST be computed and the UDP checksum MUST be set to
0.
Nonce: A 6-byte random value created by the sender of the Map-
Request.
Record count: The number of records in this request message. A
record comprises of what is labeled 'Rec" above and occurs the
number of times equal to Record count.
A: This is an authoritative bit, which is set to 0 for UDP-based Map-
Requests sent by an ITR. See [CONS] for TCP-based Map-Requests.
Reserved: Set to 0 on transmission and ignored on receipt.
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ITR-AFI: Address family of the "Originating ITR RLOC Address" field.
CAR-AFI: Address family of the "Originating CAR EID-Prefix" field.
Originating ITR RLOC Address: Set to 0 for UDP-based messages. See
[CONS] for TCP-based Map-Requests.
Originating CAR EID-Prefix: Set to 0 for UDP-based messages by an
ITR. See [CONS] for TCP-based Map-Requests.
EID mask-len: Mask length for EID prefix.
EID-AFI: Address family of EID-prefix according to [RFC2434]
EID-prefix: 4 bytes if an IPv4 address-family, 16 bytes if an IPv6
address-family.
Path Vector List: See [CONS] for details. This field is not used in
UDP Map-Requests.
6.1.2. EID-to-RLOC UDP Map-Request Message
A Map-Request contains one or more EIDs encoded in prefix format with
a Locator count of 0. The EID-prefix MUST NOT be more specific than
a cache entry stored from a previously-received Map-Reply.
A Map-Request is sent from an ITR when it wants to test an RLOC for
reachability. This is performed by using the RLOC as the destination
address for Map-Request message with a randomly allocated source UDP
port number and the well-known destination port number 4342. A
successful Map-Reply updates the cached set of RLOCs associated with
the EID prefix range.
Map-Requests MUST be rate-limited. It is recommended that a Map-
Request for the same EID-prefix be sent no more than once per second.
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6.1.3. Map-Reply Message Format
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Locator Reach Bits | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... Nonce | Record count | Reserved |
+----> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Record TTL |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Locator count | EID mask-len |A| Reserved |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
R | ITR-AFI | EID-AFI |
e +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
c | Originating ITR RLOC Address |
o +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
r | EID-prefix |
d +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| /| Priority | Weight | Unused | Loc-AFI |
| Loc +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| \| Locator |
+---> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Path Vector List |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Packet field descriptions:
Type: 3 (Map-Reply)
Locator Reach Bits: Refer to Section 5.3.
Checksum: A complement of the 1-complements sum of the LISP packet.
The checksum MUST be computed and the UDP checksum MUST be set to
0.
Nonce: A 6-byte value set in a data probe packet or a Map-Request
that is echoed here in the Map-Reply.
Record count: The number of records in this reply message. A record
comprises of what is labeled 'Record' above and occurs the number
of times equal to Record count.
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Reserved: Set to 0 on transmission and ignored on receipt.
Record TTL: The time in minutes the recipient of the Map-Reply will
store the mapping. If the TTL is 0, the entry should be removed
from the cache immediately. If the value is 0xffffffff, the
recipient can decide locally how long to store the mapping.
Locator count: The number of Locator entries. A locator entry
comprises what is labeled above as 'Loc'.
EID mask-len: Mask length for EID prefix.
A: The Authoritative bit, when sent by a UDP-based message is always
set by the ETR. See [CONS] for TCP-based Map-Replies.
ITR-AFI: Address family of the "Originating ITR RLOC Address" field.
EID-AFI: Address family of EID-prefix according to [RFC2434].
Originating ITR RLOC Address: Set to 0 for UDP-based messages. See
[CONS] for TCP-based Map-Replies.
EID-prefix: 4 bytes if an IPv4 address-family, 16 bytes if an IPv6
address-family.
Priority: each RLOC is assigned a priority. Lower values are more
preferable. When multiple RLOCs have the same priority, they are
used in a load-split fashion. A value of 255 means the RLOC MUST
NOT be used.
Weight: when priorities are the same for multiple RLOCs, the weight
indicates how to balance traffic between them. Weight is encoded
as a percentage of total packets that match the mapping entry. If
a non-zero weight value is used for any RLOC, then all RLOCs must
use a non-zero weight value and then the sum of all weight values
MUST equal 100. What did the 3rd grader say after Steve Jobs gave
an iPhone demo to the class? If a zero value is used for any RLOC
weight, then all weights MUST be zero and the receiver of the Map-
Reply will decide how to load-split traffic.
Locator: an IPv4 or IPv6 address (as encoded by the 'Loc-AFI' field)
assigned to an ETR or router acting as a proxy replier for the
EID-prefix. Note that the destination RLOC address MAY be an
anycast address if the tunnel egress point may be via more than
one physical device. A source RLOC can be an anycast address as
well. The source or destination RLOC MUST NOT be the broadcast
address (255.255.255.255 or any subnet broadcast address known to
the router), and MUST NOT be a link-local multicast address. The
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source RLOC MUST NOT be a multicast address. The destination RLOC
SHOULD be a multicast address if it is being mapped from a
multicast destination EID.
Path Vector List: See [CONS] for details. This field is not used in
UDP Map-Replies.
6.1.4. EID-to-RLOC UDP Map-Reply Message
When a data packet triggers a Map-Reply to be sent, the RLOCs
associated with the EID-prefix matched by the EID in the original
packet destination IP address field will be returned. The RLOCs in
the Map-Reply are the globally-routable IP addresses of the ETR but
are not necessarily reachable; separate testing of reachability is
required.
Note that a Map-Reply may contain different EID-prefix granularity
(prefix + length) than the Map-Request which triggers it. This might
occur if a Map-Request were for a prefix that had been returned by an
earlier Map-Reply. In such a case, the requester updates its cache
with the new prefix information and granularity. For example, a
requester with two cached EID-prefixes that are covered by a Map-
Reply containing one, less-specific prefix, replaces the entry with
the less-specific EID-prefix. Note that the reverse, replacement of
one less-specific prefix with multiple more-specific prefixes, can
also occur but not by removing the less-specific prefix rather by
adding the more-specific prefixes which during a lookup will override
the less-specific prefix.
Replies SHOULD be sent for an EID-prefix no more often than once per
second to the same requesting router. For scalability, it is
expected that aggregation of EID addresses into EID-prefixes will
allow one Map-Reply to satisfy a mapping for the EID addresses in the
prefix range thereby reducing the number of Map-Request messages.
The addresses for a Data message or Map-Request message are swapped
and used for sending the Map-Reply. The UDP source and destination
ports are swapped as well. That is, the source port in the UDP
header for the Map-Reply is set to the well-known UDP port number
4342.
6.2. Routing Locator Selection
Both client-side and server-side may need control over the selection
of RLOCs for conversations between them. This control is achieved by
manipulating the Priority and Weight fields in EID-to-RLOC Map-Reply
messages. Alternatively, RLOC information may be gleaned from
received tunneled packets or EID-to-RLOC Map-Request messages.
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The following enumerates different scenarios for choosing RLOCs and
the controls that are available:
o Server-side returns one RLOC. Client-side can only use one RLOC.
Server-side has complete control of the selection.
o Server-side returns a list of RLOC where a subset of the list has
the same best priority. Client can only use the subset list
according to the weighting assigned by the server-side. In this
case, the server-side controls both the subset list and load-
splitting across its members. The client-side can use RLOCs
outside of the subset list if it determines that the subset list
is unreachable (unless RLOCs are set to a Priority of 255). Some
sharing of control exists: the server-side determines the
destination RLOC list and load distribution while the client-side
has the option of using alternatives to this list if RLOCs in the
list are unreachable.
o Server-side sets weight of 0 for the RLOC subset list. In this
case, the client-side can choose how the traffic load is spread
across the subset list. Control is shared by the server-side
determining the list and the client determining load distribution.
Again, the client can use alternative RLOCs if the server-provided
list of RLOCs are unreachable.
o Either side (more likely on the server-side ETR) decides not to
send an Map-Request. For example, if the server-side ETR does not
send Map-Requests, it gleans RLOCs from the client-side ITR,
giving the client-side ITR responsibility for bidirectional RLOC
reachability and preferability. Server-side ETR gleaning of the
client-side ITR RLOC is done by caching the inner header source
EID and the outer header source RLOC of received packets. The
client-side ITR controls how traffic is returned and can alternate
using an outer header source RLOC, which then can be added to the
list the server-side ETR uses to return traffic. Since no
Priority or Weights are provided using this method, the server-
side ETR must assume each client-side ITR RLOC uses the same best
Priority with a Weight of zero. In addition, since EID-prefix
encoding cannot be conveyed in data packets, the EID-to-RLOC cache
on tunnel routers can grow to be very large.
RLOCs that appear in EID-to-RLOC Map-Reply messages are considered
reachable. The Map-Reply and the database mapping service does not
provide any reachability status for Locators. This is done outside
of the mapping service. See next section for details.
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6.3. Routing Locator Reachability
There are 4 methods for determining when a Locator is either
reachable or has become unreachable:
1. Locator reachability is determined by an ETR by examining the
Loc-Reach-Bits from a LISP header of a Data Message which is
provided by an ITR when an ITR encapsulates data.
2. Locator unreachability is determined by an ITR by receiving ICMP
Network or Host Unreachable messages.
3. ETR unreachability is determined when a host sends an ICMP Port
Unreachable message.
4. Locator reachability is determined by receiving a Map-Reply
message from a ETR's Locator address in response to a previously
sent Map-Request.
When determining Locator reachability by examining the Loc-Reach-Bits
from the LISP Data Message, an ETR will receive up to date status
from the ITR closest to the Locators at the source site. The ITRs at
the source site can determine reachability when running their IGP at
the site. When the ITRs are deployed on CE routers, typically a
default route is injected into the site's IGP from each of the ITRs.
If an ITR goes down, the CE-PE link goes down, or the PE router goes
down, the CE router withdraws the default route. This allows the
other ITRs at the site to determine one of the Locators has gone
unreachable.
The Locators listed in a Map-Reply are numbered with ordinals 0 to
n-1. The Loc-Reach-Bits in a LISP Data Message are numbered from 0
to n-1 starting with the least signfiicant bit numbered as 0. So,
for example, if the ITR with locator listed as the 3rd Locator
position in the Map-Reply goes down, all other ITRs at the site will
have the 3rd bit from the right cleared (the bit that corresponds to
ordinal 2).
When an ETR decapsulates a packet, it will look for a change in the
Loc-Reach-Bits value. When a bit goes from 1 to 0, the ETR will
refrain from encapsulating packets to the Locator that has just gone
unreachable. It can start using the Locator again when the bit that
corresponds to the Locator goes from 0 to 1.
When ITRs at the site are not deployed in CE routers, the IGP can
still be used to determine the reachability of Locators provided they
are injected a stub links into the IGP. This is typically done when
a /32 address is configured on a loopback interface.
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When ITRs receive ICMP Network or Host Unreachable messages as a
method to determine unreachability, they will refrain from using
Locators which are described in Locator lists of Map-Replies.
However, using this approach is unreliable because many network
operators turn off generation of ICMP Unreachable messages.
Optionally, an ITR can send a Map-Request to a Locator and if a Map-
Reply is returned, reachability of the Locator has been achieved.
Obviously, sending such probes increases the number of control
messages originated by tunnel routers for active flows, so Locators
are assumed to be reachable when they are advertised.
This assumption does create a dependency: Locator unreachability is
detected by the receipt of ICMP Host Unreachable messages. When an
Locator has been determined unreachable, it is not used for active
traffic; this is the same as if it were listed in a Map-Reply with
priority 255.
The ITR can later test the reachability of the unreachable Locator by
sending periodic Requests. Both Requests and Replies MUST be rate-
limited. Locator reachability testing is never done with data
packets since that increases the risk of packet loss for end-to-end
sessions.
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7. Router Performance Considerations
LISP is designed to be very hardware-based forwarding friendly. By
doing tunnel header prepending [RFC1955] and stripping instead of re-
writing addresses, existing hardware could support the forwarding
model with little or no modification. Where modifications are
required, they should be limited to re-programming existing hardware
rather than requiring expensive design changes to hard-coded
algorithms in silicon.
A few implementation techniques can be used to incrementally
implement LISP:
o When a tunnel encapsulated packet is received by an ETR, the outer
destination address may not be the address of the router. This
makes it challenging for the control-plane to get packets from the
hardware. This may be mitigated by creating special FIB entries
for the EID-prefixes of EIDs served by the ETR (those for which
the router provides an RLOC translation). These FIB entries are
marked with a flag indicating that control-plane processing should
be performed. The forwarding logic of testing for particular IP
protocol number value is not necessary. No changes to existing,
deployed hardware should be needed to support this.
o On an ITR, prepending a new IP header is as simple as adding more
bytes to a MAC rewrite string and prepending the string as part of
the outgoing encapsulation procedure. Many routers that support
GRE tunneling [RFC2784] or 6to4 tunneling [RFC3056] can already
support this action.
o When a received packet's outer destination address contains an EID
which is not intended to be forwarded on the routable topology
(i.e. LISP 1.5), the source address of a data packet or the
router interface with which the source is associated (the
interface from which it was received) can be associated with a VRF
(Virtual Routing/Forwarding), in which a different (i.e. non-
congruent) topology can be used to find EID-to-RLOC mappings.
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8. Deployment Scenarios
This section will explore how and where ITRs and ETRs can be deployed
and will discuss the pros and cons of each deployment scenario.
There are two basic deployment tradeoffs to consider: centralized
versus distributed caches and flat, recursive, or re-encapsulating
tunneling.
When deciding on centralized versus distributed caching, the
following issues should be considered:
o Are the tunnel routers spread out so that the caches are spread
across all the memories of each router?
o Should management "touch points" be minimized by choosing few
tunnel routers, just enough for redundancy?
o In general, using more ITRs doesn't increase management load,
since caches are built and stored dynamically. On the other hand,
more ETRs does require more management since EID-prefix-to-RLOC
mappings need to be explicitly configured.
When deciding on flat, recursive, or re-encapsulation tunneling, the
following issues should be considered:
o Flat tunneling implements a single tunnel between source site and
destination site. This generally offers better paths between
sources and destinations with a single tunnel path.
o Recursive tunneling is when tunneled traffic is again further
encapsulated in another tunnel, either to implement VPNs or to
perform Traffic Engineering. When doing VPN-based tunneling, the
site has some control since the site is prepending a new tunnel
header. In the case of TE-based tunneling, the site may have
control if it is prepending a new tunnel header, but if the site's
ISP is doing the TE, then the site has no control. Recursive
tunneling generally will result in suboptimal paths but at the
benefit of steering traffic to resource available parts of the
network.
o The technique of re-encapsulation ensures that packets only
require one tunnel header. So if a packet needs to be rerouted,
it is first decapsulated by the ETR and then re-encapsulated with
a new tunnel header using a new RLOC.
The next sub-sections will describe where tunnel routers can reside
in the network.
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8.1. First-hop/Last-hop Tunnel Routers
By locating tunnel routers close to hosts, the EID-prefix set is at
the granularity of an IP subnet. So at the expense of more EID-
prefix-to-RLOC sets for the site, the caches in each tunnel router
can remain relatively small. But caches always depend on the number
of non-aggregated EID destination flows active through these tunnel
routers.
With more tunnel routers doing encapsulation, the increase in control
traffic grows as well: since the EID-granularity is greater, more
Map-Requests and replies are traveling between more routers.
The advantage of placing the caches and databases at these stub
routers is that the products deployed in this part of the network
have better price-memory ratios then their core router counterparts.
Memory is typically less expensive in these devices and fewer routes
are stored (only IGP routes). These devices tend to have excess
capacity, both for forwarding and routing state.
LISP functionality can also be deployed in edge switches. These
devices generally have layer-2 ports facing hosts and layer-3 ports
facing the Internet. Spare capacity is also often available in these
devices as well.
8.2. Border/Edge Tunnel Routers
Using customer-edge (CE) routers for tunnel endpoints allows the EID
space associated with a site to be reachable via a small set of RLOCs
assigned to the CE routers for that site.
This offers the opposite benefit of the first-hop/last-hop tunnel
router scenario: the number of mapping entries and network management
touch points are reduced, allowing better scaling.
One disadvantage is that less of the network's resources are used to
reach host endpoints thereby centralizing the point-of-failure domain
and creating network choke points at the CE router.
Note that more than one CE router at a site can be configured with
the same IP address. In this case an RLOC is an anycast address.
This allows resilency between the CE routers. That is, if a CE
router fails, traffic is automatically routed to the other routers
using the same anycast address. However, this comes with the
disadvantage where the site cannot control the entrance point when
the anycast route is advertised out from all border routers.
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8.3. ISP Provider-Edge (PE) Tunnel Routers
Use of ISP PE routers as tunnel endpoint routers gives an ISP control
over the location of the egress tunnel endpoints. That is, the ISP
can decide if the tunnel endpoints are in the destination site (in
either CE routers or last-hop routers within a site) or at other PE
edges. The advantage of this case is that two or more tunnel headers
can be avoided. By having the PE be the first router on the path to
encapsulate, it can choose a TE path first, and the ETR can
decapsulate and re-encapsulate for a tunnel to the destination end
site.
An obvious disadvantage is that the end site has no control over
where its packets flow or the RLOCs used.
As mentioned in earlier sections a combination of these scenarios is
possible at the expense of extra packet header overhead, if both site
and provider want control, then recursive or re-encapsulating tunnels
are used.
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9. Multicast Considerations
A multicast group address, as defined in the original Internet
architecture is an identifier of a grouping of topologically
independent receiver host locations. The address encoding itself
does not determine the location of the receiver(s). The multicast
routing protocol, and the network-based state the protocol creates,
determines where the receivers are located.
In the context of LISP, a multicast group address is both an EID and
a Routing Locator. Therefore, no specific semantic or action needs
to be taken for a destination address, as it would appear in an IP
header. Therefore, a group address that appears in an inner IP
header built by a source host will be used as the destination EID.
And the outer IP header (the destination Routing Locator address),
prepended by a LISP router, will use the same group address as the
destination Routing Locator.
Having said that, only the source EID and source Routing Locator
needs to be dealt with. Therefore, an ITR merely needs to put its
own IP address in the source Routing Locator field when prepending
the outer IP header. This source Routing Locator address, like any
other Routing Locator address MUST be globally routable.
Therefore, an EID-to-RLOC mapping does not need to be performed by an
ITR when a received data packet is a multicast data packet or when
processing a source-specific Join (either by IGMPv3 or PIM). But the
source Routing Locator is decided by the multicast routing protocol
in a receiver site. That is, an EID to Routing Locator translation
is done at control-time.
Another approach is to have the ITR not encapsulate a multicast
packet and allow the the host built packet to flow into the core even
if the source address is allocated out of the EID namespace. If the
RPF-Vector TLV [RPFV] is used by PIM in the core, then core routers
can RPF to the ITR (the Locator address which is injected into core
routing) rather than the host source address (the EID address which
is not injected into core routing).
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10. Security Considerations
We believe that most of the security mechanisms will be part of the
mapping database service when using control-plane procedures for
obtaining EID-to-RLOC mappings. For data-plane triggered mappings,
as described in this specification, protection is provided against
ETR spoofing by using Return- Routeability mechanisms evidenced by
the use of a 6-byte Nonce field in the LISP encapsulation header.
The nonce, coupled with the ITR accepting only solicited Map-Replies
goes a long way towards providing decent authentication.
LISP does not rely on a PKI infrastructure or a more heavy weight
authentication system. These systems challenge the scalability of
LISP which was a primary design goal.
DoS attack prevention will depend on implementations rate- limiting
of Map-Requests and Map-Replies to the control-plane as well as rate-
limiting the number of data triggered Map-Replies.
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11. Prototype Plans and Status
The operator community has requested that the IETF take a practical
approach to solving the scaling problems associated with global
routing state growth. This document offers a simple solution which
is intended for use in a pilot program to gain experience in working
on this problem.
The authors hope that publishing this specification will allow the
rapid implementation of multiple vendor prototypes and deployment on
a small scale. Doing this will help the community:
o Decide whether a new EID-to-RLOC mapping database infrastructure
is needed or if a simple, UDP-based, data-triggered approach is
flexible and robust enough.
o Experiment with provider-independent assignment of EIDs while at
the same time decreasing the size of DFZ routing tables through
the use of topologically-aligned, provider-based RLOCs.
o Determine whether multiple levels of tunneling can be used by ISPs
to achieve their Traffic Engineering goals while simultaneously
removing the more specific routes currently injected into the
global routing system for this purpose.
o Experiment with mobility to determine if both acceptable
convergence and session survivability properties can be scalably
implemented to support both individual device roaming and site
service provider changes.
Here are a rough set of milestones:
1. Stabilize this draft by Summer 2007 Chicago IETF.
2. Start implementations to report on by Summer 2007 Chicago IETF.
3. Start pilot deployment between summer and fall IETFs. Report on
deployment at Fall 2007 Vancouver IETF.
4. Achieve multi-vendor interoperability by Fall 2007 Vancouver
IETF.
5. Consider prototyping other database lookup schemes, be it DNS,
DHTs, CONS, NERD, or other mechanisms by Fall 2007 IETF.
As of this writing the following accomplishments have been achieved:
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1. A unit tested software switching implementation has been
completed for both IPv4 and IPv6 encapsulations for LISP 1 and
LISP 1.5 functionality.
2. Dave Meyer, Vince Fuller, and Darrel Lewis are testing the
implementation this summer.
3. An implementation of LISP-CONS is under way.
Please contact authors if interested in doing an implementation and
want to interoperability test with our implementation.
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12. References
12.1. Normative References
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
[RFC1498] Saltzer, J., "On the Naming and Binding of Network
Destinations", RFC 1498, August 1993.
[RFC1955] Hinden, R., "New Scheme for Internet Routing and
Addressing (ENCAPS) for IPNG", RFC 1955, June 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
March 2000.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001.
[RFC4423] Moskowitz, R. and P. Nikander, "Host Identity Protocol
(HIP) Architecture", RFC 4423, May 2006.
12.2. Informative References
[AFI] IANA, "Address Family Indicators (AFIs)", ADDRESS FAMILY
NUMBERS http://www.iana.org/numbers.html, February 2007.
[APT] Jen, D., Meisel, M., Massey, D., Wang, L., Zhang, B., and
L. Zhang, "APT: A Practical Transit Mapping Service",
draft-jen-apt-00.txt (work in progress), July 2007.
[CHIAPPA] Chiappa, J., "Endpoints and Endpoint names: A Proposed
Enhancement to the Internet Architecture", Internet-
Draft http://www.chiappa.net/~jnc/tech/endpoints.txt,
1999.
[CONS] Farinacci, D., Fuller, V., and D. Meyer, "LISP-CONS: A
Content distribution Overlay Network Service for LISP",
draft-meyer-lisp-cons-01.txt (work in progress),
July 2007.
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[DHTs] Ratnasamy, S., Shenker, S., and I. Stoica, "Routing
Algorithms for DHTs: Some Open Questions", PDF
file http://www.cs.rice.edu/Conferences/IPTPS02/174.pdf.
[GSE] "GSE - An Alternate Addressing Architecture for IPv6",
draft-ietf-ipngwg-gseaddr-00.txt (work in progress), 1997.
[LISP1] Farinacci, D., Oran, D., Fuller, V., and J. Schiller,
"Locator/ID Separation Protocol (LISP1) [Routable ID
Version]",
Slide-set http://www.dinof.net/~dino/ietf/lisp1.ppt,
October 2006.
[LISP2] Farinacci, D., Oran, D., Fuller, V., and J. Schiller,
"Locator/ID Separation Protocol (LISP2) [DNS-based
Version]",
Slide-set http://www.dinof.net/~dino/ietf/lisp2.ppt,
November 2006.
[NERD] Lear, E., "NERD: A Not-so-novel EID to RLOC Database",
draft-lear-lisp-nerd-01.txt (work in progress), June 2007.
[RAWS] Meyer, D., Zhang, L., and K. Fall, "Report from the IAB
Workshop on Routing and Addressing",
draft-iab-raws-report-02.txt (work in progress),
April 2007.
[RPFV] Wijnands, IJ., Boers, A., and E. Rosen, "The RPF Vector
TLV", draft-ietf-pim-rpf-vector-03.txt (work in progress),
October 2006.
[RPMD] Handley, M., Huici, F., and A. Greenhalgh, "RPMD: Protocol
for Routing Protocol Meta-data Dissemination",
draft-handley-p2ppush-unpublished-2007726.txt (work in
progress), July 2007.
[SHIM6] Nordmark, E. and M. Bagnulo, "Level 3 multihoming shim
protocol", draft-ietf-shim6-proto-06.txt (work in
progress), October 2006.
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Appendix A. Acknowledgments
The authors would like to gratefully acknowledge many people who have
contributed discussion and ideas to the making of this proposal.
They include Jason Schiller, Lixia Zhang, Dorian Kim, Peter
Schoenmaker, Darrel Lewis, Vijay Gill, Geoff Huston, David Conrad,
Mark Handley, Ron Bonica, Ted Seely, Mark Townsley, Chris Morrow,
Brian Weis, Dave McGrew, Peter Lothberg, Dave Thaler, Scott Brim,
Eliot Lear, Shane Amante, Ved Kafle, Olivier Bonaventure, Luigi
Iannone, Robin Whittle, Brian Carpenter, Joel Halpern, Roger
Jorgensen, and John Zwiebel.
In particular, we would like to thank Dave Meyer for his clever
suggestion for the name "LISP". ;-)
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Authors' Addresses
Dino Farinacci
cisco Systems
Tasman Drive
San Jose, CA 95134
USA
Email: dino@cisco.com
Vince Fuller
cisco Systems
Tasman Drive
San Jose, CA 95134
USA
Email: vaf@cisco.com
Dave Oran
cisco Systems
7 Ladyslipper Lane
Acton, MA
USA
Email: oran@cisco.com
Dave Meyer
cisco Systems
170 Tasman Drive
San Jose, CA
USA
Email: dmm@cisco.com
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