draft-ietf-idr-rfc2858bis-00.txt   draft-ietf-idr-rfc2858bis-01.txt 
Network Working Group Tony Bates Network Working Group Tony Bates
Internet Draft Cisco Systems Internet Draft Cisco Systems
Expiration Date: July 2002 Ravi Chandra Expiration Date: October 2002 Ravi Chandra
Redback Networks Redback Networks
Dave Katz Dave Katz
Juniper Networks Juniper Networks
Yakov Rekhter Yakov Rekhter
Juniper Networks Juniper Networks
Multiprotocol Extensions for BGP-4 Multiprotocol Extensions for BGP-4
draft-ietf-idr-rfc2858bis-00.txt draft-ietf-idr-rfc2858bis-01.txt
1. Status of this Memo 1. Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
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material or to cite them other than as ``work in progress.'' material or to cite them other than as ``work in progress.''
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
2. Abstract 2. Abstract
Currently BGP-4 [BGP-4] is capable of carrying routing information Currently BGP-4 is capable of carrying routing information only for
only for IPv4 [IPv4]. This document defines extensions to BGP-4 to IPv4. This document defines extensions to BGP-4 to enable it to carry
enable it to carry routing information for multiple Network Layer routing information for multiple Network Layer protocols (e.g., IPv6,
protocols (e.g., IPv6, IPX, etc...). The extensions are backward IPX, etc...). The extensions are backward compatible - a router that
compatible - a router that supports the extensions can interoperate supports the extensions can interoperate with a router that doesn't
with a router that doesn't support the extensions. support the extensions.
3. Overview 3. Specification of Requirements
The only three pieces of information carried by BGP-4 that are IPv4 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
specific are (a) the NEXT_HOP attribute (expressed as an IPv4 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
address), (b) AGGREGATOR (contains an IPv4 address), and (c) NLRI document are to be interpreted as described in RFC 2119 [RFC2119].
(expressed as IPv4 address prefixes). This document assumes that any
BGP speaker (including the one that supports multiprotocol 4. Overview
The only three pieces of information carried by BGP-4 [BGP-4] that
are IPv4 specific are (a) the NEXT_HOP attribute (expressed as an
IPv4 address), (b) AGGREGATOR (contains an IPv4 address), and (c)
NLRI (expressed as IPv4 address prefixes). This document assumes that
any BGP speaker (including the one that supports multiprotocol
capabilities defined in this document) has to have an IPv4 address capabilities defined in this document) has to have an IPv4 address
(which will be used, among other things, in the AGGREGATOR (which will be used, among other things, in the AGGREGATOR
attribute). Therefore, to enable BGP-4 to support routing for attribute). Therefore, to enable BGP-4 to support routing for
multiple Network Layer protocols the only two things that have to be multiple Network Layer protocols the only two things that have to be
added to BGP-4 are (a) the ability to associate a particular Network added to BGP-4 are (a) the ability to associate a particular Network
Layer protocol with the next hop information, and (b) the ability to Layer protocol with the next hop information, and (b) the ability to
associated a particular Network Layer protocol with NLRI. To identify associated a particular Network Layer protocol with NLRI. To identify
individual Network Layer protocols this document uses Address Family, individual Network Layer protocols this document uses Address Family,
as defined in [RFC1700]. as defined in [RFC1700].
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(MP_REACH_NLRI), and Multiprotocol Unreachable NLRI (MP_REACH_NLRI), and Multiprotocol Unreachable NLRI
(MP_UNREACH_NLRI). The first one (MP_REACH_NLRI) is used to carry the (MP_UNREACH_NLRI). The first one (MP_REACH_NLRI) is used to carry the
set of reachable destinations together with the next hop information set of reachable destinations together with the next hop information
to be used for forwarding to these destinations. The second one to be used for forwarding to these destinations. The second one
(MP_UNREACH_NLRI) is used to carry the set of unreachable (MP_UNREACH_NLRI) is used to carry the set of unreachable
destinations. Both of these attributes are optional and non- destinations. Both of these attributes are optional and non-
transitive. This way a BGP speaker that doesn't support the transitive. This way a BGP speaker that doesn't support the
multiprotocol capabilities will just ignore the information carried multiprotocol capabilities will just ignore the information carried
in these attributes, and will not pass it to other BGP speakers. in these attributes, and will not pass it to other BGP speakers.
4. Multiprotocol Reachable NLRI - MP_REACH_NLRI (Type Code 14): 5. Multiprotocol Reachable NLRI - MP_REACH_NLRI (Type Code 14):
This is an optional non-transitive attribute that can be used for the This is an optional non-transitive attribute that can be used for the
following purposes: following purposes:
(a) to advertise a feasible route to a peer (a) to advertise a feasible route to a peer
(b) to permit a router to advertise the Network Layer address of (b) to permit a router to advertise the Network Layer address of
the router that should be used as the next hop to the destinations the router that should be used as the next hop to the destinations
listed in the Network Layer Reachability Information field of the listed in the Network Layer Reachability Information field of the
MP_NLRI attribute. MP_NLRI attribute.
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"Network Address of Next Hop" field as measured in octets "Network Address of Next Hop" field as measured in octets
Network Address of Next Hop: Network Address of Next Hop:
A variable length field that contains the Network Address of A variable length field that contains the Network Address of
the next router on the path to the destination system the next router on the path to the destination system
Number of SNPAs: Number of SNPAs:
A 1 octet field which contains the number of distinct SNPAs to A 1 octet field which contains the number of distinct SNPAs to
be listed in the following fields. The value 0 may be used to be listed in the following fields. The value 0 SHALL be used
indicate that no SNPAs are listed in this attribute. to indicate that no SNPAs are listed in this attribute.
Length of Nth SNPA: Length of Nth SNPA:
A 1 octet field whose value expresses the length of the "Nth A 1 octet field whose value expresses the length of the "Nth
SNPA of Next Hop" field as measured in semi-octets SNPA of Next Hop" field as measured in semi-octets
Nth SNPA of Next Hop: Nth SNPA of Next Hop:
A variable length field that contains an SNPA of the router A variable length field that contains an SNPA of the router
whose Network Address is contained in the "Network Address of whose Network Address is contained in the "Network Address of
Next Hop" field. The field length is an integral number of Next Hop" field. The field length is an integral number of
octets in length, namely the rounded-up integer value of one octets in length, namely the rounded-up integer value of one
half the SNPA length expressed in semi-octets; if the SNPA half the SNPA length expressed in semi-octets; if the SNPA
contains an odd number of semi-octets, a value in this field contains an odd number of semi-octets, a value in this field
will be padded with a trailing all-zero semi-octet. will be padded with a trailing all-zero semi-octet.
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The next hop information carried in the MP_REACH_NLRI path attribute The next hop information carried in the MP_REACH_NLRI path attribute
defines the Network Layer address of the border router that should be defines the Network Layer address of the border router that should be
used as the next hop to the destinations listed in the MP_NLRI used as the next hop to the destinations listed in the MP_NLRI
attribute in the UPDATE message. attribute in the UPDATE message.
The rules for the next hop information are the same as the rules for The rules for the next hop information are the same as the rules for
the information carried in the NEXT_HOP BGP attribute (see Section the information carried in the NEXT_HOP BGP attribute (see Section
5.1.3 of [BGP-4]). 5.1.3 of [BGP-4]).
An UPDATE message that carries the MP_REACH_NLRI must also carry the An UPDATE message that carries the MP_REACH_NLRI MUST also carry the
ORIGIN and the AS_PATH attributes (both in EBGP and in IBGP ORIGIN and the AS_PATH attributes (both in EBGP and in IBGP
exchanges). Moreover, in IBGP exchanges such a message must also exchanges). Moreover, in IBGP exchanges such a message MUST also
carry the LOCAL_PREF attribute. carry the LOCAL_PREF attribute.
An UPDATE message that carries no NLRI, other than the one encoded in An UPDATE message that carries no NLRI, other than the one encoded in
the MP_REACH_NLRI attribute, should not carry the NEXT_HOP attribute. the MP_REACH_NLRI attribute, SHOULD NOT carry the NEXT_HOP attribute.
If such a message contains the NEXT_HOP attribute, the BGP speaker If such a message contains the NEXT_HOP attribute, the BGP speaker
that receives the message should ignore this attribute. that receives the message SHOULD ignore this attribute.
5. Multiprotocol Unreachable NLRI - MP_UNREACH_NLRI (Type Code 15): An UPDATE message SHOULD NOT include the same address prefix (of the
same <AFI, SAFI>) in more than one of the following fields: WITHDRAWN
ROUTES field, Network Reachability Information fields, MP_REACH_NLRI
field, and MP_UNREACH_NLRI field. The processing of an UPDATE message
in this form is un-defined.
6. Multiprotocol Unreachable NLRI - MP_UNREACH_NLRI (Type Code 15):
This is an optional non-transitive attribute that can be used for the This is an optional non-transitive attribute that can be used for the
purpose of withdrawing multiple unfeasible routes from service. purpose of withdrawing multiple unfeasible routes from service.
The attribute is encoded as shown below: The attribute is encoded as shown below:
+---------------------------------------------------------+ +---------------------------------------------------------+
| Address Family Identifier (2 octets) | | Address Family Identifier (2 octets) |
+---------------------------------------------------------+ +---------------------------------------------------------+
| Subsequent Address Family Identifier (1 octet) | | Subsequent Address Family Identifier (1 octet) |
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A variable length field that lists NLRI for the routes that are A variable length field that lists NLRI for the routes that are
being withdrawn from service. When the Subsequent Address being withdrawn from service. When the Subsequent Address
Family Identifier field is set to one of the values defined in Family Identifier field is set to one of the values defined in
this document, each NLRI is encoded as specified in the "NLRI this document, each NLRI is encoded as specified in the "NLRI
encoding" section of this document. encoding" section of this document.
An UPDATE message that contains the MP_UNREACH_NLRI is not required An UPDATE message that contains the MP_UNREACH_NLRI is not required
to carry any other path attributes. to carry any other path attributes.
6. NLRI encoding 7. NLRI encoding
The Network Layer Reachability information is encoded as one or more The Network Layer Reachability information is encoded as one or more
2-tuples of the form <length, prefix>, whose fields are described 2-tuples of the form <length, prefix>, whose fields are described
below: below:
+---------------------------+ +---------------------------+
| Length (1 octet) | | Length (1 octet) |
+---------------------------+ +---------------------------+
| Prefix (variable) | | Prefix (variable) |
+---------------------------+ +---------------------------+
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prefix. A length of zero indicates a prefix that matches all prefix. A length of zero indicates a prefix that matches all
(as specified by the address family) addresses (with prefix, (as specified by the address family) addresses (with prefix,
itself, of zero octets). itself, of zero octets).
b) Prefix: b) Prefix:
The Prefix field contains an address prefix followed by enough The Prefix field contains an address prefix followed by enough
trailing bits to make the end of the field fall on an octet trailing bits to make the end of the field fall on an octet
boundary. Note that the value of trailing bits is irrelevant. boundary. Note that the value of trailing bits is irrelevant.
7. Subsequent Address Family Identifier 8. Subsequent Address Family Identifier
This document defines the following values for the Subsequent Address This document defines the following values for the Subsequent Address
Family Identifier field carried in the MP_REACH_NLRI and Family Identifier field carried in the MP_REACH_NLRI and
MP_UNREACH_NLRI attributes: MP_UNREACH_NLRI attributes:
1 - Network Layer Reachability Information used for unicast 1 - Network Layer Reachability Information used for unicast
forwarding forwarding
2 - Network Layer Reachability Information used for multicast 2 - Network Layer Reachability Information used for multicast
forwarding forwarding
3 - Network Layer Reachability Information used for both unicast An implementation MAY support all, some, or none of the Subsequent
and multicast forwarding Address Family Identifier values defined in this document.
8. Error Handling 9. Error Handling
If a BGP speaker receives from a neighbor an Update message that If a BGP speaker receives from a neighbor an Update message that
contains the MP_REACH_NLRI or MP_UNREACH_NLRI attribute, and the contains the MP_REACH_NLRI or MP_UNREACH_NLRI attribute, and the
speaker determines that the attribute is incorrect, the speaker must speaker determines that the attribute is incorrect, the speaker MUST
delete all the BGP routes received from that neighbor whose AFI/SAFI delete all the BGP routes received from that neighbor whose AFI/SAFI
is the same as the one carried in the incorrect MP_REACH_NLRI or is the same as the one carried in the incorrect MP_REACH_NLRI or
MP_UNREACH_NLRI attribute. For the duration of the BGP session over MP_UNREACH_NLRI attribute. For the duration of the BGP session over
which the Update message was received, the speaker then should ignore which the Update message was received, the speaker then SHOULD ignore
all the subsequent routes with that AFI/SAFI received over that all the subsequent routes with that AFI/SAFI received over that
session. session.
In addition, the speaker may terminate the BGP session over which the In addition, the speaker MAY terminate the BGP session over which the
Update message was received. The session should be terminated with Update message was received. The session SHOULD be terminated with
the Notification message code/subcode indicating "Update Message the Notification message code/subcode indicating "Update Message
Error"/"Optional Attribute Error". Error"/"Optional Attribute Error".
9. Use of BGP Capability Advertisement 10. Use of BGP Capability Advertisement
A BGP speaker that uses Multiprotocol Extensions should use the A BGP speaker that uses Multiprotocol Extensions SHOULD use the
Capability Advertisment procedures [BGP-CAP] to determine whether the Capability Advertisment procedures [BGP-CAP] to determine whether the
speaker could use Multiprotocol Extensions with a particular peer. speaker could use Multiprotocol Extensions with a particular peer.
The fields in the Capabilities Optional Parameter are set as follows. The fields in the Capabilities Optional Parameter are set as follows.
The Capability Code field is set to 1 (which indicates Multiprotocol The Capability Code field is set to 1 (which indicates Multiprotocol
Extensions capabilities). The Capability Length field is set to 4. Extensions capabilities). The Capability Length field is set to 4.
The Capability Value field is defined as: The Capability Value field is defined as:
0 7 15 23 31 0 7 15 23 31
+-------+-------+-------+-------+ +-------+-------+-------+-------+
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and ignored by the receiver. and ignored by the receiver.
SAFI - Subsequent Address Family Identifier (8 bit), encoded SAFI - Subsequent Address Family Identifier (8 bit), encoded
the same way as in the Multiprotocol Extensions. the same way as in the Multiprotocol Extensions.
A speaker that supports multiple <AFI, SAFI> tuples includes them as A speaker that supports multiple <AFI, SAFI> tuples includes them as
multiple Capabilities in the Capabilities Optional Parameter. multiple Capabilities in the Capabilities Optional Parameter.
To have a bi-directional exchange of routing information for a To have a bi-directional exchange of routing information for a
particular <AFI, SAFI> between a pair of BGP speakers, each such particular <AFI, SAFI> between a pair of BGP speakers, each such
speaker must advertise to the other (via the Capability Advertisement speaker MUST advertise to the other (via the Capability Advertisement
mechanism) the capability to support that particular <AFI, SAFI> mechanism) the capability to support that particular <AFI, SAFI>
routes. routes.
10. IANA Considerations 11. IANA Considerations
As specified in this document, the MPL_REACH_NLRI and MP_UNREACH_NLRI As specified in this document, the MPL_REACH_NLRI and MP_UNREACH_NLRI
attributes contain the Subsequence Address Family Identifier (SAFI) attributes contain the Subsequence Address Family Identifier (SAFI)
field. The SAFI name space is defined in Section 9. The IANA will field. The SAFI name space is defined in this document. The IANA will
maintain and register values for the SAFI namespace as follows. SAFI maintain and register values for the SAFI namespace as follows. SAFI
value 0 is reserved. SAFI values 1, 2, and 3 are assigned in this value 0 is reserved. SAFI values 1 and 2 are assigned in this
document. SAFI values 4 through 63 are to be assigned by IANA using document. SAFI values 4 through 63 are to be assigned by IANA using
the "IETF Consensus" policy defined in RFC2434. SAFI values 64 the "IETF Consensus" policy defined in RFC2434. SAFI values 64
through 127 are to be assigned by IANA, using the "First Come First through 127 are to be assigned by IANA, using the "First Come First
Served" policy defined in RFC2434. SAFI values 128 through 255 are Served" policy defined in RFC2434. SAFI values 128 through 255 are
for "private use", and values in this range are not to be assigned by for "private use", and values in this range are not to be assigned by
IANA. IANA.
11. Comparison with RFC2858 12. Comparison with RFC2858
This document makes the use of the next hop information consistent This document makes the use of the next hop information consistent
with the information carried in the NEXT_HOP BGP path attribute. with the information carried in the NEXT_HOP BGP path attribute.
12. Comparison with RFC2283 13. Comparison with RFC2283
This document restricts the MP_REACH_NLRI attribute to carry only a This document restricts the MP_REACH_NLRI attribute to carry only a
single instance of <AFI, SAFI, Next Hop Information, ...>. single instance of <AFI, SAFI, Next Hop Information, ...>.
This document restricts the MP_UNREACH_NLRI attribute to carry only a This document restricts the MP_UNREACH_NLRI attribute to carry only a
single instance of <AFI, SAFI, ...>. single instance of <AFI, SAFI, ...>.
This document clarifies handling of an UPDATE message that carries no This document clarifies handling of an UPDATE message that carries no
NLRI, other than the one encoded in the MP_REACH_NLRI attribute. NLRI, other than the one encoded in the MP_REACH_NLRI attribute.
This document clarifies error handling in the presence of This document clarifies error handling in the presence of
MP_REACH_NLRI or MP_UNREACH_NLRI attributes. MP_REACH_NLRI or MP_UNREACH_NLRI attributes.
This document specifies the use of BGP Capabilities Advertisements in This document specifies the use of BGP Capabilities Advertisements in
conjunction with Multi-protocol extensions. conjunction with Multi-protocol extensions.
Finally, this document includes the "IANA Consideration" Section. Finally, this document includes the "IANA Consideration" Section.
13. Security Considerations 14. Security Considerations
This extension to BGP does not change the underlying security issues This extension to BGP does not change the underlying security issues
inherent in the existing BGP. inherent in the existing BGP.
14. Acknowledgements 15. Acknowledgements
The authors would like to thank members of the IDR Working Group for The authors would like to thank members of the IDR Working Group for
their review and comments. their review and comments.
15. References 16. References
[BGP-CAP] "Capabilities Advertisement with BGP-4", R. Chandra, J. [BGP-CAP] "Capabilities Advertisement with BGP-4", R. Chandra, J.
Scudder, RFC2842, May 2000 Scudder, RFC2842, May 2000
[BGP-4] "A Border Gateway Protocol 4 (BGP-4)", Y. Rekhter & T. Li, [BGP-4] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4
draft-ietf-bgp4-17.txt (BGP-4)", RFC 1771, March 1995.
[IPv4] "Internet Protocol", J. Postel, September 1981
[RFC1700] "Assigned Numbers", J. Reynolds, J. Postel, RFC1700, [RFC1700] "Assigned Numbers", J. Reynolds, J. Postel, RFC1700,
October 1994 (see also http://www.iana.org/iana/assignments.html) October 1994 (see also http://www.iana.org/iana/assignments.html)
16. Author Information [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
17. Author Information
Tony Bates Tony Bates
Cisco Systems, Inc. Cisco Systems, Inc.
email: tbates@cisco.com email: tbates@cisco.com
Ravi Chandra Ravi Chandra
Redback Networks Redback Networks
e-mail: rchandra@redback.com e-mail: rchandra@redback.com
Dave Katz Dave Katz
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