Network Working Group E. Chen

Network Working Group E. Chen
Request for Comments: 5291 Cisco Systems
Category: Standards Track Y. Rekhter
Juniper Networks
August 2008

Outbound Route Filtering Capability for BGP-4

Status of This Memo

This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.

Abstract

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) that
the peer would use to constrain/filter its outbound routing updates
to the speaker.

1. Introduction

Currently, it is not uncommon for a BGP speaker [BGP-4] 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.

2. 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 RFC 2119 [RFC2119].

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RFC 5291 ORF Capability for BGP-4 August 2008

3. Outbound Route Filter (ORF)

This document uses the terms "Address Family Identifier (AFI)" and
"Subsequent Address Family Identifier (SAFI)". In the context of
this document, the meaning of these terms is the same as in [BGP-MP].

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 Network Layer Reachability
Information (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 is used to support matching granularity on a
per ORF entry basis. It can be either 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.

When an ORF is defined, an ORF-specific matching rule MUST be
specified so that there is no ambiguity regarding which ORF entry is
considered as the matching entry in the ORF when a route is passed
through the ORF.

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RFC 5291 ORF Capability for BGP-4 August 2008

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 MAY carry multiple ORF entries in one
or more ORFs, 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, as shown in Figures 1 and 2.

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 either 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 ORF entries" component is a two-octet field that
contains the total length (in octets) of the ORF entries that
follows for the specified ORF type.

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RFC 5291 ORF Capability for BGP-4 August 2008

+--------------------------------------------------+
| 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 ORF entries (2 octets) |
+--------------------------------------------------+
| First ORF entry (variable) |
+--------------------------------------------------+
| Second ORF entry (variable) |
+--------------------------------------------------+
| ... |
+--------------------------------------------------+
| N-th ORF entry (variable) |
+--------------------------------------------------+
| ORF Type (1 octet) |
+--------------------------------------------------+
| Length of ORF entries (2 octets) |
+--------------------------------------------------+
| First ORF entry (variable) |
+--------------------------------------------------+
| Second ORF entry (variable) |
+--------------------------------------------------+
| ... |
+--------------------------------------------------+
| N-th ORF entry (variable) |
+--------------------------------------------------+
| ... |
+--------------------------------------------------+

Figure 1: Carrying ORF Entries in the ROUTE-REFRESH Message

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RFC 5291 ORF Capability for BGP-4 August 2008

The rest of the components in the common part are encoded in the
first octet of each ORF-entry (from the most significant to the least
significant bit) as shown in Figure 2:

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 receipt.

+---------------------------------+
| Action (2 bit) |
+---------------------------------+
| Match (1 bit) |
+---------------------------------+
| Reserved (5 bits) |
+---------------------------------+
| Type specific part (variable) |
+---------------------------------+

Figure 2: ORF Entry Encoding

When the Action component of an ORF entry specifies REMOVE-ALL,
the entry consists of only the common part.

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RFC 5291 ORF Capability for BGP-4 August 2008

5. Outbound 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 Outbound Route Filtering
Capability, as described below.

The Outbound 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 entries as shown in Figure 3.

+--------------------------------------------------+
| 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) |
+--------------------------------------------------+

Figure 3: Outbound Route Filtering Capability Encoding

The use and meaning of these fields are as follows:

Address Family Identifier (AFI):

This field is the same as the one used in [BGP-MP].

Subsequent Address Family Identifier (SAFI):

This field is the same as the one used in [BGP-MP].

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RFC 5291 ORF Capability for BGP-4 August 2008

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.

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
Outbound Route Filtering Capability to the peer using BGP
Capabilities advertisement [BGP-CAP].

A BGP speaker that implements the Outbound Route Filtering Capability
MUST support the BGP ROUTE-REFRESH message, as defined in [BGP-RR].
A BGP speaker that advertises the Outbound Route Filtering Capability
to a peer using BGP Capabilities advertisement [BGP-CAP] does not
have to advertise the BGP Route Refresh Capability to that peer.

Consider a BGP speaker that advertises the Outbound Route Filtering
Capability indicating its willingness to receive a particular set of
<AFI/SAFI, ORF-Type> from its peer, and that receives the Outbound
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 is non-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 the 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 MUST
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
Outbound Route Filtering Capability indicating its willingness to
receive ORF entries from the speaker, and the speaker advertises to
the peer the Outbound Route Filtering Capability indicating its

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RFC 5291 ORF Capability for BGP-4 August 2008

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 Outbound 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 an <AFI/SAFI, ORF-type> carried by the message does not
match <AFI/SAFI, ORF-type> that the speaker is willing to receive
from the peer (as advertised to the peer in the Outbound Route
Filtering Capability), the specified ORF entries in the message are
ignored. Otherwise, the speaker modifies the specified ORF
previously received, according to the ORF entries carried in the
message. If any of the fields of an ORF entry in the message
contains an unrecognized value, the whole specified ORF previously
received is removed.

If the Action component of an ORF entry is REMOVE, but the ORF
previously received does not contain the specified entry, the ORF
entry in the message is ignored.

ORF entries with either REMOVE or REMOVE-ALL cannot 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 for that AFI/SAFI received from the
peer. The speaker MUST re-advertise all the routes that have been
affected by the ORF entries carried in the message, but MAY also re-
advertise the routes that have not been affected by the ORF entries
carried in the message.

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 ORFs
(if any) previously received from the peer.

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RFC 5291 ORF Capability for BGP-4 August 2008

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.

After a BGP speaker makes changes to the ORF entries previously sent
to a peer, the speaker MUST send to the peer the updated ORF entries
with either (a) When-to-refresh set to IMMEDIATE, or (b) When-to-
refresh set to DEFER followed by a plain ROUTE-REFRESH message. The
latter MUST be used by the speaker when there are other policy
changes (in addition to the ORF entries) that require the peer to
re-advertise all the routes.

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 removed (either via
REMOVE-ALL, or via a sequence of REMOVE).

If a particular route maintained by a BGP speaker does not 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 combining the results (combining of PERMIT and DENY
results in DENY).

7. IANA Considerations

This document defines a new BGP Capability - Outbound Route Filtering
Capability. The Capability Code for the Outbound Route Filtering
Capability is 3.

As specified in this document, an ORF entry contains the ORF-Type
field for which IANA has created and now maintains a registry
entitled "BGP Outbound Route Filtering (ORF) Types".

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RFC 5291 ORF Capability for BGP-4 August 2008

IANA maintains and registers values for ORF-Type field as follows:

- ORF-Type value 0 is reserved.

- ORF-Type values 1 through 63 are to be assigned by IANA using
either the Standards Action process defined in RFC 5226
[RFC5226], or the Early IANA Allocation process defined in RFC
4020 [RFC4020].

- ORF-Type values 64 through 127 are to be assigned by IANA, using
the "First Come First Served" policy defined in RFC 5226
[RFC5226].

- ORF-Type values 128 through 255 are vendor-specific, and values
in this range are not to be assigned by IANA.

8. Manageability Considerations

The management objects for BGP ORFs will be defined separately,
outside this document. However, it is suggested that the following
management objects be defined:

The ORF Capability object, which describes the ORF Capability
exchanged over a BGP session, should include the ORF types and the
Send/Receive values advertised and received for a BGP peer.

The ORF entry object should contain the ORF entries of each ORF sent
and received for a BGP peer.

9. Security Considerations

This extension to BGP does not change the underlying security issues
[BGP-4].

10. Acknowledgments

Some of the material in the document is adapted from a proposal for
selective updates by Yakov Rekhter, Kannan Varadhan, and Curtis
Villamizar.

11. Normative References

[BGP-4] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border
Gateway Protocol 4 (BGP-4)", RFC 4271, January 2006.

[BGP-MP] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760, January
2007.

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RFC 5291 ORF Capability for BGP-4 August 2008

[BGP-CAP] Chandra, R. and J. Scudder, "Capabilities Advertisement
with BGP-4", RFC 3392, November 2002.

[BGP-RR] Chen, E., "Route Refresh Capability for BGP-4", RFC 2918,
September 2000.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC4020] Kompella, K. and A. Zinin, "Early IANA Allocation of
Standards Track Code Points", BCP 100, RFC 4020, February
2005.

[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226, May
2008.

Authors' Addresses

Enke Chen
Cisco Systems, Inc.
170 W. Tasman Dr.
San Jose, CA 95134

Email: [email protected]

Yakov Rekhter
Juniper Networks
1194 N. Mathilda Ave
Sunnyvale, CA 94089

Email: [email protected]

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RFC 5291 ORF Capability for BGP-4 August 2008

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