One document matched: draft-ietf-idr-route-filter-00.txt
Network Working Group Enke Chen
Internet Draft Redback Networks, Inc.
Expiration Date: March 2001 Yakov Rekhter
Cisco Systems
Cooperative Route Filtering Capability for BGP-4
draft-ietf-idr-route-filter-00.txt
1. Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 except that the right to
produce derivative works is not granted.
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The list of current Internet-Drafts can be accessed at
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2. 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.
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3. 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.
4. 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
the previously installed entries in the specified ORF on the remote
peer.
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.
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4.1. 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
<Scope, Communities>. "Scope" indicates the set of routes that must
be considered by the remote peer for the given ORF request. Scope can
be one of the EXACT or NORMAL. EXACT scope indicates that the remote
peer should consider only those routes whose Communities attribute is
equal to the Communities list specified in the ORF. NORMAL scope
indicates that the remote peer should consider only those routes
whose Communities attribute either is equal to the Communities list
specified in the ORF, or exhibit a subset relation with the
Communities list specified in the ORF.
The Communities list is a list of BGP Communities.
4.2. 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 <Scope, Extended Communities>. "Scope" indicates the set
of routes that must be considered by the remote peer for the given
ORF request. Scope can be one of the EXACT or NORMAL. EXACT scope
indicates that the remote peer should consider only those routes
whose Extended Communities attribute is equal to the Extended
Communities list specified in the ORF. NORMAL scope indicates that
the remote peer should consider only those routes whose Extended
Communities attribute either is equal to the Extended Communities
list specified in the ORF, or exhibit a subset relation with the
Extended Communities list specified in the ORF.
The Extended Communities list is a list of BGP Extended Communities.
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5. Carrying ORF entries in BGP
ORF entries are carried in the BGP ROUTE-REFRESH message [BGP-RR]. 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 is to ask the peer to
refresh the routes for the AFI/SAFI carried in the message
immediately after processing the message. The semantics of DEFER
is to ask the peer to defer refreshing of all the routes until it
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.
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.
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) |
+---------------------------------+
Fig 2. ORF entry encoding
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When the Action component of an ORF entry specifies REMOVE-ALL,
the entry consists of only the common part.
5.1. 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 <Scope,
Communities>, and is encoded as follows:
Scope is a one-octet field. The EXACT Scope has the value of 1.
The NORMAL Scope has the value of 2.
Communities are encoded as a one octet Number of Communities
field, followed by one or more Communities, where each Community
is encoded as a four-octets field.
5.2. 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
<Scope, Extended Communities>, and is encoded as follows:
Scope is a one-octet field. The EXACT Scope has the value of 1.
The NORMAL Scope has the value of 2.
Extended Communities are encoded as a one octet Number of Extended
Communities field, followed by one or more Extended Communities,
where each Extended Community is encoded as a eight-octets field.
6. 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: TBD
Capability length: variable
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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) |
+--------------------------------------------------+
| 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:
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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.
7. 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.
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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.
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 should re-
advertise to the peer routes from the Adj-RIB-Out 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.
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
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).
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8. 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.
9. Security Considerations
This extension to BGP does not change the underlying security issues.
10. Acknowledgements
Some of the material in the document is "borrowed" from a proposal
for selective updates by Yakov Rekhter, Kannan Varadhan, and Curtis
Villamizar.
11. 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", draft-ietf-
idr-bgp-route-refresh-00.txt, November 1999.
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12. Author Information
Enke Chen
Redback Networks, Inc.
350 Holger Way
San Jose, CA 95134
e-mail: enke@redback.com
Yakov Rekhter
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
e-mail: yakov@cisco.com
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