Network Working Group D. Farinacci
Internet-Draft V. Fuller
Intended status: Experimental cisco Systems
Expires: September 4, 2009 March 3, 2009
LISP Map Server
draft-fuller-lisp-ms-00.txt
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Abstract
This draft describes the LISP Map-Server (LISP-MS), a computing
system which provides a simple LISP protocol interface as a "front
end" to the Endpoint-ID (EID) to Routing Locator (RLOC) mapping
database and associated virtual network of LISP protocol elements.
The purpose of the Map-Server is to simplify the implementation and
operation of LISP Ingress Tunnel Routers (ITRs) and Egress Tunnel
Routers (ETRs), the devices that implement the "edge" of the LISP
infrastructure and which connect directly to LISP-capable Internet
end sites.
Table of Contents
1. Requirements Notation . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 5
4. Basic Overview . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Interactions With Other LISP Components . . . . . . . . . . . 7
5.1. ITR EID-to-RLOC Mapping Resolution . . . . . . . . . . . . 7
5.2. ETR/Map-Server EID Prefix Registration . . . . . . . . . . 7
5.3. Map-Server Processing . . . . . . . . . . . . . . . . . . 8
5.4. Map-Resolver Processing . . . . . . . . . . . . . . . . . 8
5.4.1. Anycast Map-Resolver Operation . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . . 11
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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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
LISP [LISP] specifies an architecture and mechanism for replacing the
addresses currently used by IP with two separate name spaces: EIDs,
used within sites, and RLOCs, used on the transit networks that make
up the Internet infrastructure. To achieve this separation, LISP
defines protocol mechanisms for mapping from EIDs to RLOCs. In
addition, LISP assumes the existence of a database to store and
propagate those mappings globally. Several such databases have been
proposed, among them: LISP-CONS [CONS], LISP-NERD, [NERD] and LISP+
ALT [ALT], with LISP+ALT being the system that is currently being
implemented and deployed on the pilot LISP network.
There are two types of operation for a LISP Map-Server: as a Map-
Resolver, which accepts Map-Requests from an ITR and "resolves" the
EID-to-RLOC mapping using the distributed mapping database, and as a
Map-Server, which learns authoratative EID-to-RLOC mappings from an
ETR and publish them in the database. A single device may implement
one or both types of operation.
Conceptually, LISP Map-Servers share some of the same basic
configuration and maintenance properties as Domain Name System (DNS)
[RFC1035] servers and caching resolvers. With this in mind, this
specification borrows familiar terminology (resolver and server) from
the DNS specifications.
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3. Definition of Terms
Map-Server: a network infrastructure component which learns EID-to-
RLOC mapping entries from an authoratative source (typically, an
ETR, though static configuration or another out-of-band mechanism
may be used). A Map-Server publishes these mappings in the
distributed mapping database.
Map-Resolver: a network infrastructure component which accepts LISP
Encapsulated Map-Requests, typically from an ITR, quickly
determines whether or not the destination IP address is part of
the EID namespace; if it is not, a Negative Map-Reply is
immediately returned. Otherwise, the Map-Resolver finds the
appropriate EID-to-RLOC mapping by consulting the distributed
mapping database system.
Encapsulated Map-Request: a LISP Map-Request with an additional
LISP header prepended. Sent to UDP destination port 4341. The
"outer" addresses are globally-routeable IP addresses, also known
as RLOCs. Used by an ITR when sending to a Map-Resolver and by a
Map-Server when sending to an ETR.
Negative Map-Reply: a LISP Map-Reply that contains an empty
locator-set. Returned in response to a Map-Request of the
destination EID does not exist in the mapping database.
Typically, this means that the "EID" being requested is an IP
address connected to a non-LISP site.
Map-Register message: a LISP message sent by an ETR to a Map-Server
to register its associated EID prefixes. In addition to the set
of EID prefixes to register, the message includes one or more
RLOCs to be be used by the Map-Server when forwarding Map-Requests
(re-formatted as Encapsulated Map-Requests) received through the
database mapping system.
For definitions of other terms, notably Map-Request, Map-Reply,
Ingress Tunnel Router (ITR), and Egress Tunnel Router (ETR), please
consult the LISP specification [LISP].
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4. Basic Overview
A Map-Server is a device which publishes EID-prefix information on
behalf of ETRs and connects to the LISP distributed mapping database
system to help answer LISP Map-Requests seeking the RLOCs for those
EID prefixes. To publish its EID-prefixes, an ETR sends Map-Register
messages to the Map-Server. A Map-Register message contains a list
of EID-prefixes plus a set of RLOCs that can be used to reach the ETR
when a Map-Server needs to forward a Map-Request to it.
On the LISP pilot network, which is expected to be a model for
deployment of LISP on the Internet, a Map-Server connects to LISP+ALT
network and acts as a "last-hop" ALT router. Intermediate ALT
routers forward Map-Requests to the Map-Server that advertises a
particular EID-prefix and the Map-Server forwards them to the owning
ETR, which responds with Map-Reply messages.
The LISP Map-Server design also includes the operation of a Map-
Resolver, which receives Encapsulated Map-Requests from its client
ITRs and uses the distributed mapping database system to find the
appropriate ETR to answer those requests. On the pilot network, a
Map-Resolver acts as a "first-hop" ALT router. It has GRE tunnels
configured to other ALT routers and uses BGP to learn paths to ETRs
for different prefixes in the LISP+ALT database. The Map-Resolver
uses this path information to forward Map-Requests over the ALT to
the correct ETRs. A Map-Resolver may operate in either a non-caching
mode, where it simply de-capsulates and forwards the Encapsulated
Map-Requests that it receives from ITRs, or in caching mode, where it
saves information about those Map-Reqeusts, originates new Map-
Requests to the correct ETR, accepts and caches the Map-Replies, and
finally forwards the Map-Replies to the original ITRs.
Note that a single device can implement the functions of both a Map-
Server and a Map-Resolver. As is the case with the DNS, however,
operational simplicity argues for keeping those functions separate.
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5. Interactions With Other LISP Components
5.1. ITR EID-to-RLOC Mapping Resolution
An ITR is configured with the address of a Map-Resolver. This
address is a "locator" or RLOC in that it must be routeable on the
underlying core network; it must not need to be resolved through LISP
EID-to-RLOC mapping as that would introduce a circular dependancy.
When using a Map-Resolver, an ITR does not need to connect to any
other database mapping system. In particular, the ITR need not
connect to the LISP+ALT infrastructure or implement the BGP and GRE
protocols that it uses.
An ITR sends an Encapsulated Map-Request to a configured Map-Resolver
when it needs an EID-to-RLOC mapping that is not found in its local
map-cache. Using the Map-Resolver greatly reduces both the
complexity of the ITR implementation the costs associated with its
operation.
In response to an Encapsulated Map-Request, the ITR can expect one of
the following:
o A negative LISP Map-Reply if the Map-Resolver can determine that
the requested EID does not exist. The ITR saves EID prefix
returned in the Map-Reply in its cache, marking it as non-LISP-
capable and knows not to attempt LISP encapsulation for
destinations matching it.
o A LISP Map-Reply from the ETR that owns the EID-to-RLOC mapping or
possibly from a Map-Server answering on behalf of the ETR. Note
that the stateless nature of non-caching Map-Resolver forwarding
means that the Map-Reply may not be from the Map-Resolver to which
the Encapsulated Map-Request was sent unless the target Map-
Resolver offers caching (Section 5.4).
Note that an ITR may use a Map-Resolver while also participating in
another mapping database mechanism. For example, an ITR that runs
LISP+ALT can also send Encapsulated Map-Requests to a Map-Resolver.
When doing this, an ITR should prefer querying an ETR learned through
the ALT network as LISP+ALT provides better information about the set
of define EID prefixes. Such a configuration is expected to be very
rare, since there is little benefit to using a Map-Resolver if an ITR
is already using a mapping database system.
5.2. ETR/Map-Server EID Prefix Registration
An ETR publishes its EID prefixes to a Map-Server by sending LISP
Map-Register messages. The Map-Register message is authenticated
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using an IPSec Authentication Header (AH) as defined in [RFC2402],
with MD5 as the authentication HMAC. Prior to sending a Map-Register
message, the ETR and Map-Server must be configured with a secret
shared-key. In addition, a Map-Server will typically perform
additional verification checks, such as matching any EID-prefix
listed in a Map-Register message against a list of prefixes for which
the ETR is known to be an authoritative source.
An ETR which uses a Map-Server to publish its EID-to-RLOC mappings
does not need to participate further in the mapping database
protocol(s). On the pilot network, for example, this means that the
ETR does not need to implement GRE or BGP, which greatly simplifies
its configuration and reduces its cost of operation.
Note that use of a Map-Server does not preclude an ETR from also
connecting to the mapping database (i.e. it could also connect to the
LISP+ALT network) but doing so doesn't seem particularly useful as
the whole purpose of using a Map-Server is to avoid the complexity of
the mapping database protocols.
5.3. Map-Server Processing
The operation of a Map-Server, once it has EID-prefixes registered by
its client ETRs, is quite simple. In response to a Map-Request
(received over the ALT on the pilot network), the Map-Server verifies
that the destination EID matches an EID-prefix for which it has one
or more registered ETRs, then re-encapsulates and forwards the now-
Encapsulated Map-Reqeust to a matching ETR. It does not otherwise
alter the Map-Request so any Map-Reply sent by the ETR is returned to
the RLOC in the Map-Request, not to the Map-Server. Unless also
acting as a Map-Resolver, a Map-Server should never receive Map-
Replies; any such messages should be discarded without response,
perhaps accompanied by logging of a diagnostic message if the rate of
Map-Replies is suggestive of malicious traffic.
5.4. Map-Resolver Processing
In response to an Encapsulated Map-Request, a Map-Resolver de-
capsulates the message then checks its local database of mapping
entries (statically configured, cached, or learned from associated
ETRs). If it finds a matching entry, it returns a non-authoratative
LISP Map-Reply with the known mapping.
If the Map-Resolver does not have the mapping entry and if it can
determine that the requested IP address does not match an EID-prefix
in the mapping database, it immediately returns a negative LISP Map-
Reply, one which contains an EID prefix and an empty locator-set. To
minimize the number of negative cache entries needed by an ITR, the
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Map-Resolver should return the least-specific prefix which both
matches the original query and does not match any EID-prefix known to
exist in the LISP-capable infrastructure.
If the Map-Resolver does not have sufficient information to know
whether the EID exists, it needs to forward the Map-Request to
another device which has more information about the EID being
requested. This is done in one of two ways:
1. A non-caching Map-Resolver simply forwards the unencapsulated
Map-Request, with the original ITR RLOC as the source, on to the
distributed mapping database. On the pilot network, the Map-
Resolver is connected to the ALT network and sends the Map-
Request to the next ALT hop learned from its ALT BGP neighbors.
The Map-Resolver does not send any response to the ITR; since the
source RLOC is that of the ITR, the ETR or Map-Server which
receives the Map-Request over the ALT and responds will do so
directly to the ITR.
2. A caching Map-Resolver queues information from the Encapsulated
Map-Request, including the ITR RLOC and the original nonce. It
then modifies the Map-Request to use its own RLOC, generates a
"local nonce" (which is also saved in the request queue entry),
and forwards the Map-Request as above. When the Map-Resolver
receives a Map-Reply, it looks in its request queue to match the
reply nonce to a "local nonce" entry then de-queues the entry and
uses the saved original nonce and ITR RLOC to re-write those
fields in the Map-Reply before sending to the ITR. The request
queue entry is also deleted and the mapping entries from the Map-
Reply are saved in the Map-Resolver's cache.
5.4.1. Anycast Map-Resolver Operation
A Map-Resolver can be set up to use "anycast", where where the same
address is assigned to multiple Map-Resolvers and is propagated
through IGP routing, to facilitate the use of a topologically-close
Map-Resolver each ITR. Note that Map-Server associations with ETRs
should NOT use anycast addresses as doing so could cause
unpredictable forwarding of Map-Requests to the ETRs.
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6. Security Considerations
Using the 2-way nonce exchange documented in [LISP] can be used to
avoid ITR spoofing attacks.
To publish an authoratative EID-to-RLOC mapping, an ETR uses the
IPsec AH to authenticate itself to a Map-Server. A pair-wise shared
key is used with MD5. A key-chaining scheme may also be employed to
facilitate re-keying as needed. ESP is not used, since the mapping
data is considered to be public and does not need to be encrypted for
transport.
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7. References
7.1. Normative References
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2402] Kent, S. and R. Atkinson, "IP Authentication Header",
RFC 2402, November 1998.
7.2. Informative References
[ALT] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "LISP
Alternative Topology (LISP-ALT)",
draft-fuller-lisp-alt-05.txt (work in progress),
March 2009.
[CONS] Farinacci, D., Fuller, V., and D. Meyer, "LISP-CONS: A
Content distribution Overlay Network Service for LISP",
draft-meyer-lisp-cons-03.txt (work in progress),
November 2007.
[LISP] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis,
"Locator/ID Separation Protocol (LISP)",
draft-farcinacci-lisp-12.txt (work in progress),
March 2009.
[NERD] Lear, E., "NERD: A Not-so-novel EID to RLOC Database",
draft-lear-lisp-nerd-04.txt (work in progress),
January 2008.
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Appendix A. Acknowledgments
The authors would also like to thank the operational community for
feedback on the previous mapping database mechanisms.
Special thanks are due to Noel Chiappa for his extensive work on
caching with LISP-CONS, some of which will be used by Map-Resolvers.
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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
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