Network Working Group V. Fuller
Internet-Draft D. Farinacci
Intended status: Experimental cisco Systems
Expires: October 29, 2011 April 27, 2011
LISP Map Server
draft-ietf-lisp-ms-08.txt
Abstract
This draft describes the LISP Map-Server (LISP-MS), a computing
system which provides a simplified 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 reduce implementation and
operational complexity 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.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 29, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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publication of this document. Please review these documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 4
3. Basic Overview . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Interactions With Other LISP Components . . . . . . . . . . . 6
4.1. ITR EID-to-RLOC Mapping Resolution . . . . . . . . . . . . 6
4.2. ETR/Map-Server EID Prefix Registration . . . . . . . . . . 7
4.3. Map-Server Processing . . . . . . . . . . . . . . . . . . 8
4.4. Map-Resolver Processing . . . . . . . . . . . . . . . . . 8
4.4.1. Anycast Map-Resolver Operation . . . . . . . . . . . . 10
5. Open Issues and Considerations . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.1. Normative References . . . . . . . . . . . . . . . . . . . 14
8.2. Informative References . . . . . . . . . . . . . . . . . . 14
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
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1. 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].
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 authoritative 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.
Note that while this document assumes a LISP+ALT database mapping
infrastructure to illustrate certain aspects of Map-Server and Map-
Resolver operation, this is not intended to preclude the use of Map-
Servers and Map-Resolvers as a standardized interface for ITRs and
ETRs to access other mapping database systems.
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2. Definition of Terms
Map-Server: a network infrastructure component which learns EID-to-
RLOC mapping entries from an authoritative source (typically, an
ETR, via the registration mechanism described below). 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 carried within an
Encapsulated Control Message, which has an additional LISP header
prepended. Sent to UDP destination port 4342. 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 forwarding a Map-Request to an ETR.
Negative Map-Reply: a LISP Map-Reply that contains an empty
locator-set. Returned in response to a Map-Request if 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. An ETR may request that the Map-Server
answer Map-Requests on its behalf by setting the "proxy-map-reply"
flag (P-bit) in the message.
Map-Notify message: a LISP message sent by a Map-Server to an ETR
to confirm that a Map-Register has been received and processed.
An ETR requests that a Map-Notify be returned by setting the
"want-map-notify" or "M" bit in the Map-Register message.
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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3. 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 periodically 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.
When LISP+ALT is used as the mapping database, a Map-Server connects
to 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 a LISP+ALT 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 a non-caching mode,
where it simply de-capsulates and forwards the Encapsulated Map-
Requests that it receives from ITRs.
Alternatively, a Map-Resolver may operate in a caching mode, where it
saves information about outstanding Map-Requests, originates new Map-
Requests to the correct ETR(s), accepts and caches the Map-Replies,
and finally forwards the Map-Replies to the original ITRs. One
significant issue with use of caching in a Map-Resolver is that it
hides the original ITR source of a Map-Request, which prevents an ETR
from tailoring its responses to that source; this reduces the inbound
traffic- engineering capability for the site owning the ETR. In
addition, caching in a Map-Resolver exacerbates problems associated
with old mappings being cached; an outdated, cached mapping in an ITR
affects only that ITR and traffic originated by its site while an
outdate, cached mapping in a Map-Resolver could cause a problem with
a wider scope. More experience with caching Map-Resolvers on the
LISP pilot network will be needed to determine whether their use can
be recommended.
Note that a single device can implement the functions of both a Map-
Server and a Map-Resolver and, in many cases, the functions will be
co-located in that way.
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4. Interactions With Other LISP Components
4.1. 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 dependency.
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 4.4).
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 defined 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. There would be, for
example, no need for such an ITR to send a Map-Request to a possibly
non-existent EID (and rely on Negative Map-Replies) if it can consult
the ALT database to verify that an EID-prefix is present before
sending that Map-Request.
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4.2. ETR/Map-Server EID Prefix Registration
An ETR publishes its EID-prefixes on a Map-Server by sending LISP
Map-Register messages. A Map-Register message includes
authentication data, so prior to sending a Map-Register message, the
ETR and Map-Server must be configured with a secret shared-key. A
Map-Server's configuration must also include a list of the EID-
prefixes for which each ETR is authoritative. Upon receipt of a Map-
Register from an ETR, a Map-Server accepts only EID-prefixes that are
configured for that ETR. Failure to implement such a check would
leave the mapping system vulnerable to trivial EID-prefix hijacking
attacks. As developers and operators gain experience with the
mapping system, additional, stronger security measures may be added
to the registration process.
Map-Register messages are sent periodically from an ETR to a Map-
Server with a suggested interval between messages of one minute. A
Map-Server should time-out and remove an ETR's registration if it has
not received a valid Map-Register message within the past three
minutes. When first contacting a Map-Server after restart or changes
to its EID-to-RLOC database mappings, an ETR may initially send Map-
Register messages at an increased frequency, up to one every 20
seconds. This "quick registration" period is limited to five minutes
in duration.
An ETR may request that a Map-Server explicitly acknowledge receipt
and processing of a Map-Register message by setting the "want-map-
notify" ("M" bit) flag. A Map-Server that receives a Map-Register
with this flag set will respond with a Map-Notify message. Typical
use of this flag by an ETR would be to set it on Map-Requests sent
during the initial "quick registration" with a Map Server but then
set it only occasionally during steady-state maintenance of its
association with that Map Server.
Note that a one-minute minimum registration interval during
maintenance of an ETR-MS association does set a lower-bound on how
quickly and how frequently a mapping database entry can be updated.
This may have implications for what sorts of mobility can supported
directly by the mapping system. For a discussion on one way that
faster mobility may be implemented for individual devices, please see
[LISP-MN].
An ETR may also request, by setting the "proxy-map-reply" flag
(P-bit) in the Map-Regsiter message, that a Map-Server answer Map-
Requests instead of forwarding them to the ETR. See [LISP] for
details on how the Map-Server sets certain flags (such as those
indicating whether the message is authoritative and how returned
locators should be treated) when sending a Map-Reply on behalf of an
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ETR.
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). When using a LISP+ALT mapping database, 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.
4.3. Map-Server Processing
Once a Map-Server has EID-prefixes registered by its client ETRs, it
can accept and process Map-Requests for them. In response to a Map-
Request (received over the ALT if LISP+ALT is in use), 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 resulting Encapsulated Map-Request 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.
A Map-Server may also receive a Map-Request that is contained inside
of an Encapsulated Control Message (an Encapsulated Map-Request) with
the "Security" bit (S-bit) set. It processes the security parameters
as described in [LISP-SEC] then generates an Encapsulated Map-Request
to be sent as described above.
Note that a Map-Server that is sending a Map-Reply on behalf of an
ETR must perform security processing for that ETR as well; see
[LISP-SEC] for details.
4.4. Map-Resolver Processing
Upon receipt of an Encapsulated Map-Request, a Map-Resolver de-
capsulates the enclosed message then searches for the requested EID
in its local database of mapping entries (statically configured,
cached, or learned from associated ETRs). If it finds a matching
entry, it returns a non-authoritative LISP Map-Reply with the known
mapping.
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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
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. Using a LISP+ALT mapaping
database, 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.
If a Map-Resolver receives a Map-Request contained in an Encapsulated
Control Message (an Encapsulated Map-Request) with the "security"
option (S-Bit) set, additional processing is required. It extracts
the enclosed Map-Request and uses the attached security paramaters to
generate a new Encapsulated Control Message containing the original
Map-Rqeuest and additional signature information used to protect both
the Map-Request and the Map-Reply that will be generated by the
destination ETR or Map-Server. The outgoing message will have the
S-bit set, will use the requested EID as its outer header destination
IP address plus Map-Resolver RLOC as source IP address, and will
include security parameters added by the Map-Resolver. See
[LISP-SEC] for details of the checks that are performed and the
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security information that is added during the de-encapsulation and
re-encapsulation process.
4.4.1. Anycast Map-Resolver Operation
A Map-Resolver can be set up to use "anycast", 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 registrations need to be established between an ETR and
a specific set of Map-Servers, each identified by a specific
registation association.
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5. Open Issues and Considerations
There are a number of issues with the Map-Server and Map-Resolver
design that are not yet completely understood. Among these are:
o Feasibility, performance, and complexity trade-offs of
implementing caching in Map-Resolvers
o Convergence time when an EID-to-RLOC mapping changes and
mechanisms for detecting and refreshing or removing stale, cached
information
o Deployability and complexity trade-offs of implementing stronger
security measures in both EID-prefix registration and Map-Request/
Map-Reply processing
o Requirements for additional state in the registration process
between Map-Servers and ETRs
The authors expect that experimentation on the LISP pilot network
will help answer open questions surrounding these and other issues.
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6. IANA Considerations
This document makes no request of the IANA.
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7. Security Considerations
The 2-way nonce exchange documented in [LISP] can be used to avoid
ITR spoofing attacks.
To publish an authoritative EID-to-RLOC mapping with a Map-Server, an
ETR includes authentication data that is a hash of the message using
pair-wise shared key. An implementation must support use of HMAC-
SHA-1-160 [RFC2104] and should support use of HMAC-SHA-256-128
[RFC4634] (SHA-256 truncated to 128 bits).
During experimental and prototype deployment, authentication key
changes will be manual. Should LISP and its components be considered
for IETF standardization, further work will be required to follow the
BCP 107 [RFC4107] recommendations on automated key management.
As noted in Section 4.2, a Map-Server should verify that all EID-
prefixes registered by an ETR match configuration stored on the Map-
Server.
[LISP-SEC] defines a mechanism for providing origin authentication,
integrity, anti-reply protection, and prevention of man-in-the-middle
and "overclaiming" attacks on the Map-Request/Map-Reply exchange.
While beyond the scope of securing an individual Map-Server or Map-
Resolver, it should be noted that a BGP-based LISP+ALT network (if
ALT is used as the mapping database infrastructure) can take
advantage of technology being developed by the IETF SIDR working
group or either S-BGP [I-D.murphy-bgp-secr] or soBGP
[I-D.white-sobgparchitecture] should they be developed and widely
deployed.
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8. References
8.1. Normative References
[ALT] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "LISP
Alternative Topology (LISP-ALT)",
draft-ietf-lisp-alt-06.txt (work in progress), March 2011.
[LISP] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis,
"Locator/ID Separation Protocol (LISP)",
draft-ietf-lisp-12.txt (work in progress), April 2011.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
February 1997.
[RFC4634] Eastlake, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and HMAC-SHA)", RFC 4634, July 2006.
8.2. Informative References
[CONS] Farinacci, D., Fuller, V., and D. Meyer, "LISP-CONS: A
Content distribution Overlay Network Service for LISP",
draft-meyer-lisp-cons-04.txt (work in progress),
April 2008.
[I-D.murphy-bgp-secr]
Murphy, S., "BGP Security Analysis",
draft-murphy-bgp-secr-04 (work in progress),
November 2001.
[I-D.white-sobgparchitecture]
White, R., "Architecture and Deployment Considerations for
Secure Origin BGP (soBGP)",
draft-white-sobgparchitecture-00 (work in progress),
May 2004.
[LISP-MN] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "LISP
Mobile Node Architecture", draft-meyer-lisp-mn-04.txt
(work in progress), February 2011.
[LISP-SEC]
Maino, F., Ermagan, V., Cabellos, A., Sanchez, D., and O.
Bonaventure, "LISP-Security", draft-maino-lisp-sec-00.txt
(work in progress), March 2011.
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[NERD] Lear, E., "NERD: A Not-so-novel EID to RLOC Database",
draft-lear-lisp-nerd-08.txt (work in progress),
March 2010.
[RFC4107] Bellovin, S. and R. Housley, "Guidelines for Cryptographic
Key Management", BCP 107, RFC 4107, June 2005.
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Appendix A. Acknowledgments
The authors would like to thank Greg Schudel, Darrel Lewis, John
Zwiebel, Andrew Partan, Dave Meyer, Isidor Kouvelas, Jesper Skriver,
Fabio Maino, and members of the lisp@ietf.org mailing list for their
feedback and helpful suggestions.
Special thanks are due to Noel Chiappa for his extensive work on
caching with LISP-CONS, some of which may be used by Map-Resolvers.
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Authors' Addresses
Vince Fuller
cisco Systems
Tasman Drive
San Jose, CA 95134
USA
Email: vaf@cisco.com
Dino Farinacci
cisco Systems
Tasman Drive
San Jose, CA 95134
USA
Email: dino@cisco.com
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