Network Working Group Enke Chen
Internet Draft Cisco Systems
Expiration Date: June 2005 Yakov Rekhter
Juniper Networks
Cooperative Route Filtering Capability for BGP-4
draft-ietf-idr-route-filter-11.txt
Status of this Memo
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By submitting this Internet-Draft, I certify that any applicable
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Abstract
This document defines a BGP-based mechanism that allows a BGP speaker
to send to its BGP peer a set of route filters that the peer would
use to constrain/filter its outbound routing updates to the speaker.
1. Specification of Requirements
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 [RFC2119].
2. Introduction
Currently it is not uncommon for a BGP speaker to receive, and then
filter out some unwanted routes from its peers based on its local
routing policy. Since the generation and transmission of routing
updates by the sender, as well as the processing of routing updates
by the receiver consume resources, it may be beneficial if the
generation of such unwanted routing updates can be avoided in the
first place.
This document defines a BGP-based mechanism that allows a BGP speaker
to send to its BGP peer a set of Outbound Route Filters (ORFs). The
peer would then apply these filters, in addition to its locally
configured outbound filters (if any), to constrain/filter its
outbound routing updates to the speaker.
3. Outbound Route Filter (ORF)
Conceptually an ORF entry is a tuple of the form <AFI/SAFI, ORF-Type,
Action, Match, ORF-value>; an ORF consists of one or more ORF entries
that have a common AFI/SAFI and ORF-Type. An ORF is identified by
<AFI/SAFI, ORF-Type>.
The "AFI/SAFI" component provides a coarse granularity control by
limiting the ORF to only the routes whose NLRI matches the "AFI/SAFI"
component of the ORF.
The "ORF-Type" component determines the content of the ORF-value.
The "Action" component controls handling of the ORF Request by the
remote peer. Action can be one of ADD, REMOVE, REMOVE-ALL. ADD adds
an ORF entry to the ORF on the remote peer; REMOVE deletes a
previously installed ORF entry on the remote peer; REMOVE-ALL deletes
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the previously installed entries in the specified ORF on the remote
peer.
The "Match" component is used if support matching granularity on a
per ORF entry basis is needed, in which case the "Match" component
can be one of PERMIT or DENY. The semantics of PERMIT is to ask the
peer to pass updates for the set of routes that match the ORF entry.
The semantics of DENY is to ask the peer not to pass updates for the
set of routes that match the ORF entry.
3.1. Communities ORF-Type
The Community ORF-Type allows to express ORFs in terms of BGP
Communities [BGP-COMMUNITIES]. That is, the Communities ORF-Type
provides Communities-based route filtering.
Conceptually the ORF-value of the Communities ORF-Type consists of a
single Community.
The sender SHOULD set the value of the Match field to PERMIT; the
receiver SHOULD ignore the value of the Match field.
The remote peer should consider only those routes whose Communities
attribute has at least one Community in common with the Communities
list specified in the ORF.
3.2. Extended Communities ORF-Type
The Extended Community ORF-Type allows to express ORFs in terms of
BGP Extended Communities [BGP-EXT-COMMUNITIES]. That is, the Extended
Communities ORF-Type provides Extended Communities-based route
filtering.
Conceptually the ORF-value of the Extended Communities ORF-Type
consists of a single Extended Community.
The sender SHOULD set the value of the Match field to PERMIT; the
receiver SHOULD ignore the value of the Match field.
The remote peer should consider only those routes whose Extended
Communities attribute has at least one Extended Community in common
with the Extended Communities list specified in the ORF.
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4. Carrying ORF entries in BGP
ORF entries are carried in the BGP ROUTE-REFRESH message [BGP-RR].
A BGP speaker can distinguish an incoming ROUTE-REFRESH message that
carries one or more ORF entries from an incoming plain ROUTE-REFRESH
message by using the Message Length field in the BGP message header.
A single ROUTE-REFRESH message could carry multiple ORF entries, as
long as all these entries share the same AFI/SAFI.
From the encoding point of view each ORF entry consists of a common
part and type-specific part.
The common part consists of <AFI/SAFI, ORF-Type, Action, Match>, and
is encoded as follows:
The AFI/SAFI component of an ORF entry is encoded in the AFI/SAFI
field of the ROUTE-REFRESH message.
Following the AFI/SAFI component is the one-octet When-to-refresh
field. The value of this field can be one of IMMEDIATE (0x01) or
DEFER (0x02). The semantics of IMMEDIATE and DEFER are discussed
in the "Operation" section of this document.
Following the When-to-refresh field is a collection of one or more
ORFs, grouped by ORF-Type.
The ORF-Type component is encoded as a one-octet field.
The Length of ORFs component is a two-octets field that contains
the length (in octets) of the ORF entries that follows.
+--------------------------------------------------+
| Address Family Identifier (2 octets) |
+--------------------------------------------------+
| Reserved (1 octet) |
+--------------------------------------------------+
| Subsequent Address Family Identifier (1 octet) |
+--------------------------------------------------+
| When-to-refresh (1 octet) |
+--------------------------------------------------+
| ORF Type (1 octet) |
+--------------------------------------------------+
| Length of ORFs (2 octets) |
+--------------------------------------------------+
| First ORF entry (variable) |
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+--------------------------------------------------+
| Second ORF entry (variable) |
+--------------------------------------------------+
.........
+--------------------------------------------------+
| N-th ORF entry (variable) |
+--------------------------------------------------+
| ORF Type (1 octet) |
+--------------------------------------------------+
| Length of ORFs (2 octets) |
+--------------------------------------------------+
| First ORF entry (variable) |
+--------------------------------------------------+
| Second ORF entry (variable) |
+--------------------------------------------------+
.........
+--------------------------------------------------+
| N-th ORF entry (variable) |
+--------------------------------------------------+
.........
Fig 1. Carrying ORF entries in the ROUTE-REFRESH message
The rest of the components in the common part are encoded in first
octet of each ORF-entry as follows (from the most significant to the
least significant bit):
Action is a two-bit field. The value of this field is 0 for ADD, 1
for REMOVE, and 2 for REMOVE-ALL.
Match is a one-bit field. The value of this field is 0 for PERMIT
and 1 for DENY. This field is significant only when the value of
the Action field is either ADD or REMOVE.
Reserved is a 5-bit field. It is set to 0 on transmit and ignored
on receive.
+---------------------------------+
| Action (2 bit) |
+---------------------------------+
| Match (1 bit) |
+---------------------------------+
| Reserved (5 bits) |
+---------------------------------+
| Type specific part (variable) |
+---------------------------------+
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Fig 2. ORF entry encoding
When the Action component of an ORF entry specifies REMOVE-ALL,
the entry consists of only the common part.
4.1. Type specific encoding (Communities ORF-Type)
The value of the ORF-Type for the Communities ORF-Type is 2.
The type-specific part of Communities ORF-Type consists of single
Community encoded as a four-octets field.
4.2. Type specific encoding (Extended Communities ORF-Type)
The value of the ORF-Type for the Extended Communities ORF-Type is 3.
The type-specific part of Extended Communities ORF-Type consists of a
single Extended Community encoded as an eight-octets field.
5. Cooperative Route Filtering Capability
A BGP speaker that is willing to receive ORF entries from its peer,
or a BGP speaker that would like to send ORF entries to its peer
advertises this to the peer by using the Cooperative Route Filtering
Capability, as described below.
The Cooperative Route Filtering Capability is a new BGP capability
[BGP-CAP] defined as follows:
Capability code: 3
Capability length: variable
Capability value: one or more of the following entries:
+--------------------------------------------------+
| Address Family Identifier (2 octets) |
+--------------------------------------------------+
| Reserved (1 octet) |
+--------------------------------------------------+
| Subsequent Address Family Identifier (1 octet) |
+--------------------------------------------------+
| Number of ORFs (1 octet) |
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+--------------------------------------------------+
| ORF Type (1 octet) |
+--------------------------------------------------+
| Send/Receive (1 octet) |
+--------------------------------------------------+
| ... |
+--------------------------------------------------+
| ORF Type (1 octet) |
+--------------------------------------------------+
| Send/Receive (1 octet) |
+--------------------------------------------------+
Fig 4. Capability encoding
The use and meaning of these fields are as follows:
Address Family Identifier (AFI):
This field carries the identity of the Network Layer protocol
associated with the Network Address that follows. Presently
defined values for this field are specified in RFC1700 (see the
Address Family Numbers section).
Subsequent Address Family Identifier (SAFI):
This field provides additional information about the type of
the Network Layer Reachability Information carried in the
attribute.
Number of ORF Types:
This field contains the number of Filter Types to be listed in
the following fields.
ORF Type:
This field contains the value of an ORF Type.
Send/Receive:
This field indicates whether the sender is (a) willing to
receive ORF entries from its peer (value 1), (b) would like to
send ORF entries to its peer (value 2), or (c) both (value 3)
for the ORF Type that follows.
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6. Operation
A BGP speaker that is willing to receive ORF entries from its peer,
or would like to send ORF entries to its peer SHOULD advertise the
Cooperative Route Filtering Capability to the peer using BGP
Capabilities advertisement [BGP-CAP].
A BGP speaker that implements the Cooperative Route Filtering
Capability must support BGP ROUTE-REFRESH message, as defined in
[BGP-RR]. A BGP speaker that advertises the Cooperative Route
Filtering Capability to a peer using BGP Capabilities advertisement
[BGP-CAP] doesn't have to advertise the BGP Route Refresh capability
to that peer.
Consider a BGP speaker that advertises the Cooperative Route
Filtering Capability indicating its willingness to receive a
particular set of <AFI, SAFI, ORF-Type> from its peer, and that
receives the Cooperative Route Filtering Capability indicating the
desire of the peer to send a particular set <AFI, SAFI, ORF-Type> to
the speaker. If for a given <AFI, SAFI> the intersection between
these two sets are not-empty, the speaker SHOULD NOT advertise to the
peer any routes with that <AFI, SAFI> prior to receiving from the
peer any ROUTE-REFRESH message carrying that <AFI, SAFI>, where the
message could be either without any ORF entries, or with one or more
ORF entry and When-to-refresh field set to IMMEDIATE. If, on the
other hand, for a given <AFI, SAFI> the intersection between these
two sets is empty, the speaker SHOULD follow normal BGP procedures.
A BGP speaker may send a ROUTE-REFRESH message with one or more ORF
entries to its peer only if the peer advertises to the speaker the
Cooperative Route Filtering Capability indicating its willingness to
receive ORF entries from the speaker, and the speaker advertises to
the peer the Cooperative Route Filtering Capability indicating its
desire to send ORF entries to the peer. The message may contain only
ORF entries of <AFI, SAFI, ORF-type> that the peer is willing to
receive, as advertised to the speaker in the Cooperative Route
Filtering Capability.
When a BGP speaker receives a ROUTE-REFRESH message with one or more
ORF entries from its peer, then the speaker performs the following
actions. If the <AFI, SAFI, ORF-type> carried by the message doesn't
match <AFI, SAFI, ORF-type> that the speaker is willing to receive
from the peer (as advertised to the peer in the Cooperative Route
Filtering Capability), the specified ORF is ignored. Otherwise, the
speaker modifies the specified ORF, as specified in the ORF entries
carried by the message. If any of the fields within an ORF entry
contain an unrecognized value, the whole specified ORF is removed.
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If the Action component of an ORF entry is REMOVE, but the ORF
doesn't contain the specified entry, the entry is ignored.
ORF entries with either REMOVE or REMOVE-ALL can not remove locally
configured outbound route filters.
If the When-to-Refresh indicates IMMEDIATE, then after processing all
the ORF entries carried in the message the speaker re-advertises to
the peer routes from the Adj-RIB-Out associated with the peer that
have the same AFI/SAFI as what is carried in the message, and taking
into account all the ORF entries received from the peer. However,
the routes that have not be affected by the ORF entries carried in
the message SHOULT NOT be re-advertised to the peer.
If the When-to-Refresh indicates DEFER, then after processing all the
ORF entries carried in the message the speaker defers re-
advertisement to the peer routes from the Adj-RIB-Out associated with
the peer that have the same AFI/SAFI as what is carried in the
message, and taking into account all the ORF entries received from
the peer until the speaker receives a subsequent ROUTE-REFRESH
message for the same AFI/SAFI either without any ORF entries, or with
one or more ORF entries and When-to-refresh set to IMMEDIATE.
If the speaker receives from the peer a ROUTE-REFRESH message without
any ORF entries, then the speaker sends to the peer all routes from
the Adj-RIB-Out associated with the peer whose AFI/SAFI is the same
as what is carried in the message and taking into account the ORF
received from the peer.
The set of ORF entries that the speaker sends to the peer expresses
the speaker's local preference, that the peer may or may not decide
to honor.
During a single BGP session the speaker may pass multiple ORF entries
to the peer.
The lifetime of an ORF is the duration of the BGP session during
which the ORF is exchanged.
An ORF is removed when the last ORF entry is remove (either via
REMOVE-ALL, or via a sequence of REMOVE).
If a particular route maintained by a BGP speaker doesn't match any
of the ORF entries of any of the (non-empty) ORFs associated with a
particular peer, then this route SHOULD NOT be advertised to the
peer.
If a BGP speaker maintains multiple ORFs of different ORF-Types for a
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particular peer, then the decision by the speaker to advertise a
route to the peer is determined by passing the route through each
such ORF, and and-ing the results (and-ing of PERMIT and DENY results
in DENY).
7. IANA Considerations
As specified in this document, an ORF enty contains the ORF-Type
field. ORF-Type value 0 is reserved. ORF-Type values 1 through 63
are to be assigned by IANA using the "IETF Consensus" policy defined
in RFC2434. ORF-Type values 64 through 127 are to be assigned by
IANA, using the "First Come First Served" policy defined in RFC2434.
ORF-Type values 128 through 255 are vendor-specific, and values in
this range are not to be assigned by IANA.
8. Security Considerations
This extension to BGP does not change the underlying security issues.
9. Intellectual Property Considerations
This section is taken from Section 10.4 of [RFC2026].
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
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10. Copyright Notice
Copyright (C) The Internet Society (year). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
11. Acknowledgements
Some of the material in the document is "borrowed" from a proposal
for selective updates by Yakov Rekhter, Kannan Varadhan, and Curtis
Villamizar.
12. Normative References
[BGP-4] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4
(BGP-4)", RFC 1771, March 1995.
[BGP-MP] Bates, T., Chandra, R., Katz, D., and Rekhter, Y.,
"Multiprotocol Extensions for BGP-4", RFC 2858, June 2000
[BGP-CAP] Chandra, R., Scudder, J., "Capabilities Advertisement with
BGP-4", RFC2842, May 2000
[BGP-COMMUNITIES] Chandra, R., Traina, P., and Li, T., "BGP
Communities Attribute", RFC1997, August 1996.
[BGP-EXT-COMMUNITIES] Ramachandra, S., Tappan, D., "BGP Extended
Communities Attribute", draft-ramachandra-bgp-ext-communities-02.txt
[BGP-RR] Chen, E., "Route Refresh Capability for BGP-4", RFC2918,
September 2000
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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13. Author Information
Enke Chen
Cisco Systems, Inc.
e-mail: enkechen@cisco.com
Yakov Rekhter
Juniper Networks
e-mail: yakov@juniper.net
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