draft-ietf-idr-deprecate-as-sets-05.txt   draft-ietf-idr-deprecate-as-sets-06.txt 
Network Working Group W. Kumari Network Working Group W. Kumari
Internet-Draft Google, Inc. Internet-Draft Google, Inc.
Intended status: BCP K. Sriram Intended status: BCP K. Sriram
Expires: January 28, 2012 U.S. NIST Expires: April 9, 2012 U.S. NIST
July 27, 2011 October 07, 2011
Deprecation of the use of BGP AS_SET, AS_CONFED_SET. Recommendation for Not Using AS_SET and AS_CONFED_SET in BGP
draft-ietf-idr-deprecate-as-sets-05 draft-ietf-idr-deprecate-as-sets-06
Abstract Abstract
This document deprecates the use of the AS_SET and AS_CONFED_SET This document recommends against the use of the AS_SET and
types of the AS_PATH in BGPv4. This is done to simplify the design AS_CONFED_SET types of the AS_PATH in BGPv4. This is done to
and implementation of the BGP protocol and to make the semantics of simplify the design and implementation of the BGP protocol and to
the originator of a route more clear. This will also simplify the make the semantics of the originator of a route more clear. This
design, implementation and deployment of ongoing work in the Secure will also simplify the design, implementation and deployment of
Inter-Domain Routing Working Group. ongoing work in the Secure Inter-Domain Routing Working Group.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 28, 2012. This Internet-Draft will expire on April 9, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements notation . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements notation . . . . . . . . . . . . . . . . . . . . . 4
3. Recommendation to Network Operators . . . . . . . . . . . . . . 4 3. Recommendation to Network Operators . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
7. Informative References . . . . . . . . . . . . . . . . . . . . 5 7. Informative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction 1. Introduction
The AS_SET path segment type of the AS_PATH attribute ([RFC4271], The AS_SET path segment type of the AS_PATH attribute ([RFC4271],
Section 4.3) is created by a router that is performing route Section 4.3) is created by a router that is performing route
aggregation and contains an unordered set of ASs that the update has aggregation and contains an unordered set of ASs that the update has
traversed. The AS_CONFED_SET path type ([RFC5065]) of the AS_PATH traversed. The AS_CONFED_SET path type ([RFC5065]) of the AS_PATH
attribute is created by a router that is performing route aggregation attribute is created by a router that is performing route aggregation
and contains an unordered set of Member AS Numbers in the local and contains an unordered set of Member AS Numbers in the local
confederation that the update has traversed. It is very similar to confederation that the update has traversed. It is very similar to
AS_SETs but is used within a confederation. AS_SETs but is used within a confederation.
By performing aggregation, a router is, in essence, combining By performing aggregation, a router is, in essence, combining
multiple existing routes into a single new route. This type of multiple existing routes into a single new route. This type of
aggregation blurs the semantics of what it means to originate a route aggregation blurs the semantics of what it means to originate a
which can cause operational issues that include reachability problems route. Said aggregation can therefore cause operational issues such
and traffic engineering issues. as not being able to authenticate a route origin for the aggregate
prefix in new BGP security technologies (such as those that take
advantage of the "X.509 Extensions for IP Addresses and AS
Identifiers" [RFC3779]). This in turn would result in reachability
problems for aggregated prefix and its components (i.e., more
specifics). Said aggregation also creates traffic engineering issues
because the precise path information for the component prefixes is
not preserved.
From analysis of past Internet routing data it is apparent that From analysis of past Internet routing data it is apparent that
aggregation that involves AS_SETs is very seldom used in practice on aggregation that involves AS_SETs is very seldom used in practice on
the public network [analysis] and, when it is used, it is usually the public network [analysis] and, when it is used, it is usually
used incorrectly -- reserved AS numbers ([RFC1930]) and / or only a used incorrectly -- reserved AS numbers ([RFC1930]) and / or only a
single AS in the AS_SET are by far the most common case. The single AS in the AS_SET are by far the most common case. Because the
reduction in table size provided by the aggregation is outweighed by aggregation involving AS_SETs is very rarely used, the reduction in
additional complexity in the BGP protocol and confusion regarding table size provided by said aggregation is extremely small, and any
what exactly is meant by originating a route. advantage thereof is outweighed by additional complexity in the BGP
protocol. As noted above, said aggregation also poses impediments to
implementation of said new BGP security technologies.
In the past AS_SET had been used in a few rare cases to allow route In the past, AS_SET had been used in a few rare cases to allow route
aggregation where two or more providers could form the same prefix, aggregation where two or more providers could form the same prefix,
using the exact match of the others prefix in some advertisement and using the exact match of the other's prefix in some advertisement and
configuring the aggregation differently elsewhere. The key to configuring the aggregation differently elsewhere. The key to
configuring this correctly was to form the aggregate at the border in configuring this correctly was to form the aggregate at the border in
the outbound BGP policy and omit prefixes from the AS that the the outbound BGP policy and omit prefixes from the AS that the
aggregate was being advertised to. The AS_SET therefore allowed this aggregate was being advertised to. The AS_SET therefore allowed this
practice without the loss of BGP's AS_PATH loop protection. This use practice without the loss of BGP's AS_PATH loop protection. This use
of AS_SET served a purpose which fell in line with the original of AS_SET served a purpose which fell in line with the original
intended use. intended use. Without use of AS_SET, aggregates must always contain
only less specific prefixes (not less than or equal to), and must
Without AS_SET aggregates must always contain only less specific never aggregate an exact match.
prefixes (not less than or equal to), and must never aggregate an
exact match. Since this practice is thought to no longer be widely
used, it is thought to be safe to deprecate the use of AS_SET.
2. Requirements notation 2. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Recommendation to Network Operators 3. Recommendation to Network Operators
Operators are strongly advised to not generate any new announcements It is RECOMMENDED that operators not generate any new announcements
containing AS_SETs or AS_CONFED_SETs. If they have already announced containing AS_SETs or AS_CONFED_SETs. If they have already announced
routes with AS_SETs or AS_CONFED_SETs in them, then they should routes with AS_SETs or AS_CONFED_SETs in them, then they SHOULD
withdraw and re-announce those prefixes without AS_SETs in the withdraw those routes and re-announce routes for the component
updates. This may require undoing the aggregation that was prefixes (i.e., the more specifics of the previously aggregated
previously performed, and announcing more specifics. Route prefix) without AS_SETs in the updates. This involves undoing the
aggregation that was previously performed by proxy aggregation is aggregation that was previously performed (with AS_SETs), and
still possible under some conditions without the use of AS_SETs. As announcing more specifics (without AS_SETs). Route aggregation that
with any change, the operator should understand the full implications was previously performed by proxy aggregation (i.e., without the use
of the change. of AS_SETs) is still possible under some conditions. As with any
change, the operator should understand the full implications of the
change.
It is worth noting that new technologies (such as those that take It is worth noting that new technologies (such as those that take
advantage of the "X.509 Extensions for IP Addresses and AS advantage of the "X.509 Extensions for IP Addresses and AS
Identifiers" ([RFC3779]) may not support routes with AS_SETs / Identifiers" [RFC3779]) might not support routes with AS_SETs /
AS_CONFED_SETs in them, and MAY treat as infeasible routes containing AS_CONFED_SETs in them, and may treat as infeasible routes containing
them. Future BGP implementations may also do the same. them. Future BGP implementations may also do the same. It is
expected that, even before the deployment of these new or future
It is expected that, even before the deployment of these technologies, operators may filter routes with AS_SETs /
technologies, operators may begin filtering routes that contain AS_CONFED_SETs in them. Other than making that observation, this
AS_SETs or AS_CONFED_SETs. document is not intended to make any recommendation for how an
operator should behave when receiving a route with AS_SET or
AS_CONFED_SET in it. This document's focus is entirely on the sender
side as discussed in the preceding paragraph.
4. IANA Considerations 4. IANA Considerations
This document requires no IANA actions. This document requires no IANA actions.
5. Security Considerations 5. Security Considerations
This document discourages the use of aggregation techniques that This document discourages the use of aggregation techniques that
create AS_SETs. Future work may update the protocol to remove create AS_SETs. Future work may update the protocol to remove
support for the AS_SET path segment type of the AS_PATH attribute. support for the AS_SET path segment type of the AS_PATH attribute.
 End of changes. 14 change blocks. 
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