Network Working Group D. Farinacci
Internet-Draft V. Fuller
Intended status: Experimental D. Oran
Expires: July 21, 2007 cisco Systems
January 17, 2007
Locator/ID Separation Protocol (LISP)
draft-farinacci-lisp-00.txt
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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 . . . . . . . . . . . . . . . . . . . . . . 12
6. EID-to-RLOC Mapping . . . . . . . . . . . . . . . . . . . . . 14
6.1. Control-Plane Packet Format . . . . . . . . . . . . . . . 14
6.1.1. EID-to-RLOC Mapping Request Message . . . . . . . . . 16
6.1.2. EID-to-RLOC Mapping Reply Message . . . . . . . . . . 16
6.2. Routing Locator Selection and Reachability . . . . . . . . 16
7. Router Performance Considerations . . . . . . . . . . . . . . 19
8. Deployment Scenarios . . . . . . . . . . . . . . . . . . . . . 20
8.1. First-hop/Last-hop Tunnel Routers . . . . . . . . . . . . 21
8.2. Border/Edge Tunnel Routers . . . . . . . . . . . . . . . . 21
8.3. ISP Provider-Edge (PE) Tunnel Routers . . . . . . . . . . 21
9. Multicast Considerations . . . . . . . . . . . . . . . . . . . 23
10. Security Considerations . . . . . . . . . . . . . . . . . . . 24
11. Prototype Plans . . . . . . . . . . . . . . . . . . . . . . . 25
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
12.1. Normative References . . . . . . . . . . . . . . . . . . . 26
12.2. Informative References . . . . . . . . . . . . . . . . . . 26
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29
Intellectual Property and Copyright Statements . . . . . . . . . . 30
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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 may be found described as GSE
[GSE], Shim6 [SHIM6], and HIP [RFC4423]. 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.
[DHTs]
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 IP 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.
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 address today, typically through a DNS lookup. The
source EID is obtained via existing mechanisms used to set a hosts
"local" IP address. LISP uses PI blocks for EIDs; such EIDs MUST
NOT be used as a 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.
End-system: is an IP device that originates packets with a single
IP 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
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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).
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.
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
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 to RLOC mappings. Each potential ETR
typically contains a small piece of the database: the EID-to-RLOC
mappings for the EIDs "behind" the router. These map to one of
the router's own, globally-visible, IP addresses. This block of
EIDs which map to a particular RLOC is described as an "EID
prefix". Pieces of the database may also be aggregated and may be
contained in other routers that "proxy" reply for ETRs.
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.
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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 IP
header an ITR prepends or an ETR strips.
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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.
o EIDs are not expected to be usable for end-to-end communication in
the absence of an EID-to-RLOC mapping operation.
o EID prefixes are likely to be hierarchically assigned in a manner
which is optimized for administrative convenience and to
facilitate scaling of the EID-to-RLOC mapping database.
o EIDs may also be structured (subnetted) in a manner suitable for
local routing within an autonomous system.
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An additional LISP header may be pre-pended to packets by a transit
router 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 ETR within the
ISP (along intra-ISP traffic engineered path) or in an 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 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:
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 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 packet is built using the EIDs in the IP 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 it's RLOCs as the source IP
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address and uses the destination EID from the original packet
header as the destination IP address.
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 ICMP EID-to-RLOC Mapping
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 ICMP
message is one of the ETR's RLOCs (one of the RLOCs that is
embedded in the ICMP payload).
5. The ITR receives the ICMP 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
in selecting an RLOC. See section Section 6 for more details.
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5. Tunneling Details
This section describes the tunnel header details. LISP uses the
existing, IP-in-IP encapsulation as described below.
LISP IP-in-IP 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 = 4 | Header Checksum |
\ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | Source Routing Locator |
\ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | Destination Routing Locator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ |Version| IHL |Type of Service| Total Length |
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Identification |Flags| Fragment Offset |
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IH | Time to Live | Protocol | Header Checksum |
\ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | Source EID |
\ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | Destination EID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Header IH is the inner header, preserved from the datagram received
from the originating host. The source and destination IP addresses
are EIDs.
Header OH 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 "IP in IP encapsulation" from
[RFC2003].
When doing Recursive Tunneling:
o The OH header Time to Live field SHOULD be copied from the IH
header Time to Live field.
o The OH header Type of Service field SHOULD be copied from the IH
header Type of Service field.
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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.
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6. EID-to-RLOC Mapping
6.1. Control-Plane Packet Format
When LISP 1 or LISP 1.5 are used, a new ICMP packet type encodes 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 = 1 | Header Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Routing Locator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Routing Locator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 42 | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Record Count | Unused |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RLOC Count | EID Mask Len | EID Prefix 1 ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Priority | Weight | Routing Locator 1 ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Priority | Weight | Routing Locator n ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . . . |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Locator Count | EID Mask Len | EID Prefix n ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Priority | Weight | Routing Locator 1 ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Priority | Weight | Routing Locator n ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Packet field descriptions:
ICMP Type - set to 42 for an "EID-to-RLOC Mapping" message.
ICMP Code - 1 is a Request, 2 is a Reply.
ICMP Checksum - 1's complement checksum of the entire ICMP packet.
Unused - transmitted as 0 and ignored on receipt.
Record Count - unassigned number of records contained in the
message. A record contains a mapping of an EID-prefix to a set of
RLOCs. A record count of 0 is illegal.
RLOC Count - The number of RLOCs associated with this EID prefix.
EID Mask Len - The mask length of the EID prefix. By encoding an
EID prefix, a set of RLOCs can be associated with a block of EIDs.
Values are between 0 and 32 inclusive.
EID Prefix - the encoded EID, represented as an IP address. This
field is 4 bytes in length.
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
should 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. 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. Going to buy an
iPhone? If a zero value is used for any RLOC weight, then all
weights must be zero and the receiver of the Reply will decide how
to load-split traffic.
Routing Locator (RLOC) - an IP address assigned to an ETR or router
acting as a proxy replier for the EID-prefix. Note that the RLOC
address can be an anycast address if the tunnel egress point may
be via more than one physical device. The source or destination
RLOC MUST NEVER be the broadcast address (255.255.255.255). The
source RLOC MUST NEVER be a multicast address. The destination
RLOC SHOULD be a multicast address if it is being mapped from a
multicast destination EID.
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6.1.1. EID-to-RLOC Mapping Request Message
A Request contains one or more EIDs encoded in prefix format with a
Locator count of 0. The EID-prefix should be no more specific than a
cache entry stored from a previously-received Reply.
A request is sent from an ITR when it wants to test an RLOC for
reachability. This testing is performed by using the RLOC as the
destination address for type of ICMP packet. A successful reply
updates the cached set of RLOCs associated with the EID prefix range.
Requests MUST be rate-limited. It is recommended that a Request for
the same EID-prefix be sent no more than once per second.
6.1.2. EID-to-RLOC Mapping Reply Message
When a data packet triggers a Reply to be sent, the RLOC associated
with the EID-prefix matched by the EID in the original packet
destination IP address field will be returned. The RLOCs in the
Reply are the globally-routable IP addresses of the ETR but are not
necessarily reachable; separate testing of reachability is required.
Note that a Reply may contain different EID-prefix granularity
(prefix + length) than the Request which triggers it. This might
occur if a Request were for a prefix that had been returned by an
earlier 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 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 blocks of EIDs into EID-prefixes will
allow one Reply to suppress further Requests for multiple EIDs in the
EID-prefix range.
6.2. Routing Locator Selection and Reachability
Both client-side and server-side may need control over the selection
RLOCs for conversations between them. This control is achieved by
manipulating the Priority and Weight fields in ICMP EID-to-RLOC
Mapping Reply messages. Alternatively, RLOC information may be
gleaned from received tunneled packets or ICMP EID-to-RLOC Mapping
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Request messages.
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) decides not send an
ICMP EID-to-RLOC Mapping Request. For example, if the server-side
does not send Requests, it gleans RLOCs from the client-side,
giving the client-side responsibility for bidirectional RLOC
reachability and preferability. Server-side gleaning of the
client-side RLOC is done by caching the inner header source EID
and the outer header source RLOC of received packets. The client-
side 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 uses to return traffic. Since no Priority or Weights
are provided using this method, the server-side must assume each
client-side 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.
An RLOC in the list returned by a EID-to-RLOC Mapping Reply is only
known to be reachable when an EID-to-RLOC Mapping Request sent using
it as the destination IP address results in the a successful reply
containing it as a source IP address. Obviously, sending such probes
increases the number of control messages originated by tunnel routers
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for active flows, so RLOC as assumed to be reachable when they are
advertised.
This assumption does create a dependency: RLOC unreachability is
detected by the receipt of ICMP Host Unreachable messages. When an
RLOC has been determined unreachable, it is not used for active
traffic; this is the same as if it is listed in a Mapping Reply with
priority 255.
The ITR can later test the reachability of the unreachable RLOC by
sending periodic Requests. Both Requests and Replies MUST be rate-
limited. RLOC 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 can 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 or 6to4 tunneling 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 is was received) can be associated with a
VRF, 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 ingress 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-Locator
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-Locator 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
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 be also deployed in edge switches. These
devices generally have layer-2 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.
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
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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 (the destination EID) 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. 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.
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10. Security Considerations
ICMP EID-to-RLOC Reply messages are authoritative to the same extent
DNS Replies are. LISP is no less secure than DNS and at this time we
do not intend to add any additional security mechanisms to the
proposal.
However, in future versions of this draft, we will add cryptographic
authenticity to ICMP EID-to-RLOC messages.
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11. Prototype Plans
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, ICMP-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 Spring 2007 Prague IETF.
2. Start implementation to report on by Spring 2007 Prague IETF.
3. Start pilot deployment between spring and summer IETFs. Report
on deployment at Summer 2007 Chicago IETF.
4. Achieve multi-vendor interoperability by Summer 2007 Chicago
IETF.
5. Consider prototyping other database lookup schemes, be it DNS,
DHTs, or other mechanisms by Fall 2007 IETF.
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12. References
12.1. Normative References
[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.
[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003,
October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4423] Moskowitz, R. and P. Nikander, "Host Identity Protocol
(HIP) Architecture", RFC 4423, May 2006.
12.2. Informative References
[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.
[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.
[RAWS] Meyer, D., Zhang, L., and K. Fall, "Report from the IAB
Workshop on Routing and Addressing",
draft-iab-raws-report-00.txt (work in progress),
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November 2006.
[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 Dave Meyer, Jason Schiller, Lixia Zhang, Dorian Kim,
Peter Schoenmaker, Darrel Lewis, Vijay Gill, Geoff Huston, David
Conrad, Ron Bonica, Ted Seely, Mark Townsley, Chris Morrow, Brian
Weis, and Dave McGrew.
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
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Full Copyright Statement
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