Inter-Domain Routing P. Lapukhov
Internet-Draft Facebook
Intended status: Standards Track October 31, 2016
Expires: May 4, 2017
Use of BGP for dissemination of ILA mapping information
draft-lapukhov-bgp-ila-afi-02
Abstract
Identifier-Locator Addressing [I-D.herbert-nvo3-ila] relies on
splitting the 128-bit IPv6 address into identifier and locator parts
to implement identifier mobility, and network virtualization. This
document proposes a method for distributing the identifier to locator
mapping information using Multiprotocol Extensions for BGP-4
[RFC4760].
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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
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This Internet-Draft will expire on May 4, 2017.
Copyright Notice
Copyright (c) 2016 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. BGP ILA AFI . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Capability Advertisement . . . . . . . . . . . . . . . . . . 3
4. Disseminating Identifier-Locator mapping information . . . . 3
4.1. Advertising ILA mapping information . . . . . . . . . . . 3
4.2. Withdrawing ILA mapping information . . . . . . . . . . . 4
5. Interpreting the mapping information . . . . . . . . . . . . 4
5.1. Unicast SAFI . . . . . . . . . . . . . . . . . . . . . . 4
5.2. Multicast SAFI . . . . . . . . . . . . . . . . . . . . . 5
6. Inter-domain mapping exchange . . . . . . . . . . . . . . . . 5
7. BGP Next-Hop attribute handling with ILA . . . . . . . . . . 6
8. Use of Add-Paths extension with ILA AFI . . . . . . . . . . . 7
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
10. Manageability Considerations . . . . . . . . . . . . . . . . 7
11. Security Considerations . . . . . . . . . . . . . . . . . . . 8
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
13.1. Normative References . . . . . . . . . . . . . . . . . . 8
13.2. Informative References . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Under the ILA proposal, IPv6 address is split in 64-bit identifier
(lower address bits) and locator (higher address bits) portions. The
locator part is determined dynamically from a mapping table that
maintains associations between the location-independent identifiers
and topologically significant locators. The hosts that collectively
implement and maintain such mappings are referred to as "ILA domain"
in this document. The ILA domain has a globally unique 64-bit SIR
(Standard Identifier Representation) prefix assigned to it (see
[I-D.herbert-nvo3-ila] for more details on SIR prefix use).
This document proposes a new address family identifier (AFI) for the
purpose of disseminating the locator-identifier mappings among the
nodes participating in the ILA domain. For example, this extension
could be used to propagate the mappings from ILA hosts to ILA routers
and allow the routers to perform their function (see
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[I-D.herbert-nvo3-ila] for definition of the "ILA router" functions).
Additional information that provides more detailed examples of
deployment scenarios using BGP could be found in
[I-D.lapukhov-ila-deployment].
2. BGP ILA AFI
This document introduces a new AFI known as a "Identifier-Locator
Addressing AFI" (ILA AFI) with the actual value to be assigned by
IANA. The purpose of this AFI is disseminating the mapping
information in the ILA domain, e.g. between ILA hosts and ILA
routers. This document defines the use of SAFI values of "1"
(unicast) and "2" (multicast) only.
3. Capability Advertisement
A BGP speaker that wishes to exchange ILA mapping information MUST
use the Multiprotocol Extensions Capability Code, as defined in
[RFC4760], to advertise the corresponding AFI/SAFI pair.
4. Disseminating Identifier-Locator mapping information
4.1. Advertising ILA mapping information
For the purpose of ILA mapping encoding, the 8-octet locator field
SHALL be encoded in the "next-hop address" field. The "length of the
next-hop address" MUST be set to "8". The identifiers bound to the
locator SHALL be encoded within the NLRI portion of MP_REACH_NLRI
attribute. The NLRI portion of MP_REACH_NLRI starts with the two-
octet "Length of identifiers" field, with the value being multiple of
8. The rest of the NLRI is a collection of 8-octet identifiers that
are bound to the locator specified in the "next-hop address" field.
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+---------------------------------------------------------+
| Address Family Identifier (2 octets) |
+---------------------------------------------------------+
| Subsequent Address Family Identifier (1 octet) |
+---------------------------------------------------------+
| Length of Next Hop Address (1 octet, set to "8") |
+---------------------------------------------------------+
| Locator value (8 octets) |
+---------------------------------------------------------+
| Reserved (1 octet), must be zero |
+---------------------------------------------------------+
| Length of NLRI field (2 octets, multiple of 8) |
+---------------------------------------------------------+
| Identifiers (variable, 8 octets each) |
+---------------------------------------------------------+
Figure 1: MP_REACH_NLRI Layout
4.2. Withdrawing ILA mapping information
Withdrawal of ILA mapping information is performed via an
MP_UNREACH_NLRI attribute advertisement organized as following:
+---------------------------------------------------------+
| Address Family Identifier (2 octets) |
+---------------------------------------------------------+
| Subsequent Address Family Identifier (1 octet) |
+---------------------------------------------------------+
| Length of witdrawn identifiers (2 octets) |
+---------------------------------------------------------+
| Identifiers (variable, 8 octets each) |
+---------------------------------------------------------+
Figure 2: MP_UNREACH_NLRI Layout
5. Interpreting the mapping information
5.1. Unicast SAFI
Only the locator part of ILA address is used for packet routing, and
every node that hosts an identifier is expected to have a unique /64
prefix routable within the scope of the ILA domain. The identifiers
advertised under the ILA AFI are expected to be used by the data-
plane implementation to perform match on a full IPv6 address and
decide whether the locator portion of the address needs a re-write.
It is up to the implementation to decide which full 128-bit IPv6
addresses need a rewrite, e.g. by matching on a Standard Identifier
Representation (SIR) prefix as defined in [I-D.herbert-nvo3-ila].
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The locator rewrite information comes from the next-hop "address"
associated with the identifier. The next-hop field of MP_REACH_NLRI
attribute in general is not expected to be used for any routing
resolutions/lookups by the BGP process. It should primarily be used
to create a rewrite rule in the data-plane forwarding table. The
actual forwarding decision is then based on subsequent lookup in the
forwarding table to find the next hop to send the packet to.
In some scenarios, resolving the next-hop attribute via additional
lookups tables might be necessary. For example, for environments
that deploy MPLS ([RFC3031]) forwarding, the locator may resolve to a
label stack that is required to perform further forwarding. In this
case, the ILA address rewrite will be accompanied by additional
actions, such as label stack imposition. These decisions have to be
made in implementation dependant fashion.
5.2. Multicast SAFI
Multicast SAFI retain the same encoding format, with a different SAFI
value. For multicast packets, the RPF check process SHALL be
modified for use with ILA source addresses. Specifically, source ILA
IPv6 addresses with the identifier portion matching the mapping table
SHALL be mapped to proper locator, prior to performing the RPF check.
The ILA source addresses need to be identified by some means specific
to ILA implementation, e.g. by matching on configured SIR prefixes.
The ILA addresses that do not match any mapping entry SHALL be
considered as failing the RPF check.
6. Inter-domain mapping exchange
The ILA mappings are only unique with an ILA domain - it is possible
that different domains may re-use the same identifiers. To make
identifiers globally unique, they MUST be concatenated with the SIR
prefix assigned to each ILA domain. These globally unique
identifiers may then be exchanged between multiple ILA domains. IANA
will be requested to allocate new SAFI value called "VPN-ILA" SAFI to
facilitate exchange of inter-domain ILA mappings. The MP_REACH_NLRI
attributes exchanged over this SAFI will look as following:
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+---------------------------------------------------------+
| Address Family Identifier (2 octets) |
+---------------------------------------------------------+
| Subsequent Address Family Identifier (1 octet) |
+---------------------------------------------------------+
| SIR prefix (8 octets) |
+---------------------------------------------------------+
| Length of Next Hop Address (1 octet, set to "8") |
+---------------------------------------------------------+
| Locator value (8 octets) |
+---------------------------------------------------------+
| Reserved (1 octet), must be zero |
+---------------------------------------------------------+
| Length of NLRI field (2 octets, multiple of 8) |
+---------------------------------------------------------+
| Identifiers (variable, 8 octets each) |
+---------------------------------------------------------+
The main difference from the Unicast/Multicast SAFI's is presence of
the SIR prefix field in the announcement. Correspondingly, the
MP_UNREACH_NLRI will look as following:
+---------------------------------------------------------+
| Address Family Identifier (2 octets) |
+---------------------------------------------------------+
| Subsequent Address Family Identifier (1 octet) |
+---------------------------------------------------------+
| SIR Prefix (8 bytes) |
+---------------------------------------------------------+
| Length of witdrawn identifiers (2 octets) |
+---------------------------------------------------------+
| Identifiers (variable, 8 octets each) |
+---------------------------------------------------------+
The use of domain-specific identifiers would require the ILA hosts
and routers to make their ILA cache lookups based on the full 128-bit
prefix.
7. BGP Next-Hop attribute handling with ILA
This document proposes that the BGP next-hop attribute value encode
the locator associated with all identifiers found in MP_REACH_NLRI
attribute. It is possible that an intermediate speaker may change
the next-hop value. This may be required to ensure all traffic for
the associated identifiers is routed through that intermediate
speaker. The speaker is expected to maintain the original ILA
mappings in its mapping table, and perform additional destination
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address translation for the ILA packets. This way, a form of loose
hop traffic engineering could be realized within an ILA domain.
It is common that BGP implementations reset the next-hop value for
announcements made over eBGP sessions. Such scenario may be common
between two different ILA domains.
8. Use of Add-Paths extension with ILA AFI
It could be useful to bind multiple locators to the same identifier,
e.g. for the purpose of load-sharing. To make announcing multiple
locators possible, the MP_REACH_NLRI and MP_REACH_NLRI attributes are
extended to encode the path-identifier per [I-D.ietf-idr-add-paths],
correspondingly enabling the capability for the AFI/SAFI.
Specifically, the NLRI field will look as following:
+---------------------------------------------------------+
| Path identifier (4 octets) |
+---------------------------------------------------------+
| Length of NLRI field (2 octets, multiple of 8) |
+---------------------------------------------------------+
| Identifiers (variable, 8 octets each) |
+---------------------------------------------------------+
Such encoding instructs the receiver to create multiple locator
entries for an identifier, differentiated by their path identifiers.
Optionally, a weight could be associated with each path using the
"link bandwidth" extended community defined in
[I-D.ietf-idr-link-bandwidth]
9. IANA Considerations
For the purpose of this work, IANA would be asked to allocate a value
for the new AFI, and the VPN-ILA SAFI.
10. Manageability Considerations
The ILA mappings distribution is likely to be done using separate
infrastructure, independent from the BGP topology used for regular
routing information distribution. Most likely there will be a
collection of iBGP route-reflectors deployed within each ILA domain,
and peering with a BGP process running on each ILA router and ILA
host. More details and deployment examples could be found in
[I-D.lapukhov-ila-deployment].
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11. Security Considerations
This document does not introduce any changes in terms of BGP
security. Defining ILA security model is outside of scope of this
document.
12. Acknowledgements
The author would like to thank Doug Porter for the original idea and
discussion of this proposal.
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001,
<http://www.rfc-editor.org/info/rfc3031>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<http://www.rfc-editor.org/info/rfc4271>.
[I-D.ietf-idr-add-paths]
Walton, D., Retana, A., Chen, E., and J. Scudder,
"Advertisement of Multiple Paths in BGP", draft-ietf-idr-
add-paths-15 (work in progress), May 2016.
[I-D.ietf-idr-link-bandwidth]
Mohapatra, P. and R. Fernando, "BGP Link Bandwidth
Extended Community", draft-ietf-idr-link-bandwidth-06
(work in progress), January 2013.
13.2. Informative References
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<http://www.rfc-editor.org/info/rfc4760>.
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[I-D.herbert-nvo3-ila]
Herbert, T., "Identifier-locator addressing for IPv6",
draft-herbert-nvo3-ila-03 (work in progress), October
2016.
[I-D.lapukhov-ila-deployment]
Lapukhov, P., "Deploying Identifier-Locator Addressing
(ILA) in datacenter", draft-lapukhov-ila-deployment-00
(work in progress), March 2016.
Author's Address
Petr Lapukhov
Facebook
1 Hacker Way
Menlo Park, CA 94025
US
Email: petr@fb.com
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