Internet DRAFT - draft-xu-src-dst-bgp
draft-xu-src-dst-bgp
Network Working Group M. Xu
Internet-Draft S. Yang
Expires: September 22, 2016 J. Wu
Tsinghua University
March 21, 2016
Source/Destination Routing Using BGP-4
draft-xu-src-dst-bgp-00
Abstract
This document describes the changes necessary for BGP-4 to route
traffic from a specified prefix to a specified prefix.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Theory of Routing . . . . . . . . . . . . . . . . . . . . . . 3
3. Extended NLRI Encodings . . . . . . . . . . . . . . . . . . . 3
4. Dealing with Ambiguity . . . . . . . . . . . . . . . . . . . 4
5. Src-Dst Capability . . . . . . . . . . . . . . . . . . . . . 4
6. Compatibility Considerations . . . . . . . . . . . . . . . . 5
7. Deployment Issues . . . . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . 5
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
10.1. Normative References . . . . . . . . . . . . . . . . . . 5
10.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
This specification builds on BGP-4 [RFC4271]. It defines the
extended NLRI encodings for an appended source prefix, to define
routes from a source prefix to a destination prefix.
Traditionally, routing protocols make routing decisions solely based
on destination IP addresses, packets towards the same destination
will be delivered to the same next hop no matter where they come
from. However, considering policy-based routing, traffic engineering
and security, source information is also important for making routing
decisions.
In this document, we extend the NLRI field to support source prefix.
This implies not simply routing "to a destination", but routing "to
that destination AND from a specified source". Traffic within the
network could be source/destination routed as well, or could be
implicitly or explicitly routed from "any prefix", ::/0.
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1.1. 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 [RFC2119].
2. Theory of Routing
The primary function of BGP is to exchange network reachability
information, compute the routes towards destination prefixes, and
select the best routes according the pre-defined selection rules.
BGP-4 can support only those policies which conform to the
destination-based forwarding paradigm.
In this context, the route is qualified by a source prefix.
Intrinsically, in traditional routing model, the object being routed
to is a destination prefix; in the new routing model, the object
being routed might be a destination prefix given that the packet
sports a certain source prefix.
Routes that lack a source prefix match any source prefix (i.e.,
::/0), by definition.
3. Extended NLRI Encodings
In order to carry the source prefix information in an UPDATE message,
the existing NLRI encodings are extended by prepending the source
prefix.
The NLRI encodings specified in [RFC4271] and [RFC4760] are extended
as following:
+--------------------------------+
| Type (4 octets) |
+--------------------------------+
| Length (1 octet) |
+--------------------------------+
| Prefix (variable) |
+--------------------------------+
Extended NLRI Encodings based on RFC4271 and RFC4760
and the NLRI encoding specified in [RFC3107] is extended as the
following:
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+--------------------------------+
| Type (4 octets) |
+--------------------------------+
| Length (1 octet) |
+--------------------------------+
| Label (3 octets) |
+--------------------------------+
| ... |
+--------------------------------+
| Prefix (variable) |
+--------------------------------+
Extended NLRI encodings based on RFC3107
Type: Assinged by IANA.
Length: Indicates the length in bits of the IP address prefix.
Label: Carrying label information as defined in [RFC3107]
Prefix: The Prefix field contains an IP address prefix, followed by
enough trailing bits to make the end of the field fall on an octet
boundary.
4. Dealing with Ambiguity
Ambiguity could happen when there are two routes: A and B, where
source prefix of A is more specific than source prefix of B, and
destination prefix of B is more specific than destination prefix of
A.
In this context, the matching rule follows that in
[I-D.baker-ipv6-ospf-dst-src-routing], the FIB lookup MUST yield the
route with the longest matching destination prefix that also matches
the source prefix constraint. In the event of a tie on the
destination prefix, it MUST also match the longest matching source
prefix among those options.
5. Src-Dst Capability
The capability to carry both source and destination prefixes in BGP
udpate messages (src-dst capability) is a new BGP capability
[RFC5492]. The Capability Code for this capability is specified in
the IANA. The Capability Length field of this capability is zero.
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6. Compatibility Considerations
To be compatible with [I-D.ietf-idr-add-paths], the Type field
(defined in Section Section 3) should be carefully defined by IANA.
7. Deployment Issues
Router without src-dst capability should discard the BGP messages
with extended NRLI, and it falls back to traditional destination-
based routing when this happens.
8. Security Considerations
While source/destination routing could be used as part of a security
solution, it could be considered similar to an access list that is
managed by and scales with routing.
9. IANA Considerations
The Type field in Section Section 3, and the new capability code
should be defined by IANA.
10. References
10.1. Normative References
[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>.
[RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement
with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
2009, <http://www.rfc-editor.org/info/rfc5492>.
[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>.
[RFC3107] Rekhter, Y. and E. Rosen, "Carrying Label Information in
BGP-4", RFC 3107, DOI 10.17487/RFC3107, May 2001,
<http://www.rfc-editor.org/info/rfc3107>.
[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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10.2. Informative References
[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-10 (work in progress), October 2014.
[I-D.baker-ipv6-ospf-dst-src-routing]
Baker, F., "IPv6 Source/Destination Routing using OSPFv3",
draft-baker-ipv6-ospf-dst-src-routing-03 (work in
progress), August 2013.
Authors' Addresses
Mingwei Xu
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R. China
Phone: +86-10-6278-1572
Email: xumw@tsinghua.edu.cn
Shu Yang
Graduate School at Shenzhen, Tsinghua University
Division of Information Science and Technology
Shenzhen 518055
P.R. China
Phone: +86-755-2603-6059
Email: yang.shu@sz.tsinghua.edu.cn
Jianping Wu
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R. China
Phone: +86-10-6278-5983
Email: jianping@cernet.edu.cn
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