draft-ietf-idr-rfc2858bis-02.txt   draft-ietf-idr-rfc2858bis-03.txt 
Network Working Group Tony Bates (Cisco Systems) Network Working Group Tony Bates (Cisco Systems)
Internet Draft Ravi Chandra (Redback Networks) Internet Draft Ravi Chandra (Redback Networks)
Expiration Date: October 2002 Dave Katz (Juniper Networks) Expiration Date: January 2004 Dave Katz (Juniper Networks)
Obsoles RFC2858 Yakov Rekhter (Juniper Networks) Obsoles RFC2858 Yakov Rekhter (Juniper Networks)
Multiprotocol Extensions for BGP-4 Multiprotocol Extensions for BGP-4
draft-ietf-idr-rfc2858bis-02.txt draft-ietf-idr-rfc2858bis-03.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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are IPv4 specific are (a) the NEXT_HOP attribute (expressed as an are IPv4 specific are (a) the NEXT_HOP attribute (expressed as an
IPv4 address), (b) AGGREGATOR (contains an IPv4 address), and (c) IPv4 address), (b) AGGREGATOR (contains an IPv4 address), and (c)
NLRI (expressed as IPv4 address prefixes). This document assumes that NLRI (expressed as IPv4 address prefixes). This document assumes that
any BGP speaker (including the one that supports multiprotocol 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
individual Network Layer protocols this document uses Address Family, identify individual Network Layer protocols associated with the next
as defined in [RFC1700]. hop information and semantics of NLRI this document uses a
combination of Address Family, as defined in [RFC1700], and
Subsequent Address Family (as described in this document).
One could further observe that the next hop information (the One could further observe that the next hop information (the
information provided by the NEXT_HOP attribute) is meaningful (and information provided by the NEXT_HOP attribute) is meaningful (and
necessary) only in conjunction with the advertisements of reachable necessary) only in conjunction with the advertisements of reachable
destinations - in conjunction with the advertisements of unreachable destinations - in conjunction with the advertisements of unreachable
destinations (withdrawing routes from service) the next hop destinations (withdrawing routes from service) the next hop
information is meaningless. This suggests that the advertisement of information is meaningless. This suggests that the advertisement of
reachable destinations should be grouped with the advertisement of reachable destinations should be grouped with the advertisement of
the next hop to be used for these destinations, and that the the next hop to be used for these destinations, and that the
advertisement of reachable destinations should be segregated from the advertisement of reachable destinations should be segregated from the
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| Second SNPA (variable) | | Second SNPA (variable) |
+---------------------------------------------------------+ +---------------------------------------------------------+
| ... | | ... |
+---------------------------------------------------------+ +---------------------------------------------------------+
| Length of Last SNPA (1 octet) | | Length of Last SNPA (1 octet) |
+---------------------------------------------------------+ +---------------------------------------------------------+
| Last SNPA (variable) | | Last SNPA (variable) |
+---------------------------------------------------------+ +---------------------------------------------------------+
| Network Layer Reachability Information (variable) | | Network Layer Reachability Information (variable) |
+---------------------------------------------------------+ +---------------------------------------------------------+
The use and meaning of these fields are as follows: The use and meaning of these fields are as follows:
Address Family Identifier: Address Family Identifier (AFI):
This field carries the identity of the Network Layer protocol This field in combination with the Subsequent Address Family
associated with the Network Address that follows. Presently Identifier field identifies the Network Layer protocol
defined values for this field are specified in RFC1700 (see the associated with the Network Address of Next Hop and the
Address Family Numbers section). semantics of the Network Layer Reachability Information that
follows.
Subsequent Address Family Identifier: Presently defined values for the Address Family Identifier
field are specified in RFC1700 (see the Address Family Numbers
section).
This field provides additional information about the type of Subsequent Address Family Identifier (SAFI):
the Network Layer Reachability Information carried in the
attribute. This field in combination with the Address Family Identifier
field identifies the Network Layer protocol associated with the
Network Address of the Next Hop and the semantics of the
Network Layer Reachability Information that follows.
Length of Next Hop Network Address: Length of Next Hop Network Address:
A 1 octet field whose value expresses the length of the A 1 octet field whose value expresses the length of the
"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. The
Network Layer protocol associated with the Network Address of
the Next Hop is identified by a combination of <AFI, SAFI>
carried in the attribute.
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 SHALL be used be listed in the following fields. The value 0 SHALL be used
to 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
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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.
Network Layer Reachability Information: Network Layer Reachability Information (NLRI):
A variable length field that lists NLRI for the feasible routes A variable length field that lists NLRI for the feasible routes
that are being advertised in this attribute. When the that are being advertised in this attribute. The semantics of
Subsequent Address Family Identifier field is set to one of the NLRI is identified by a combination of <AFI, SAFI> carried in
values defined in this document, each NLRI is encoded as the attribute.
specified in the "NLRI encoding" section of this document.
When the Subsequent Address Family Identifier field is set to
one of the values defined in this document, each NLRI is
encoded as specified in the "NLRI encoding" section of this
document.
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 router that should be used
used as the next hop to the destinations listed in the MP_NLRI as the next hop to the destinations listed in the MP_NLRI attribute
attribute in the UPDATE message. 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.
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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) |
+---------------------------------------------------------+ +---------------------------------------------------------+
| Withdrawn Routes (variable) | | Withdrawn Routes (variable) |
+---------------------------------------------------------+ +---------------------------------------------------------+
The use and the meaning of these fields are as follows: The use and the meaning of these fields are as follows:
Address Family Identifier: Address Family Identifier (AFI):
This field carries the identity of the Network Layer protocol This field in combination with the Subsequent Address Family
associated with the NLRI that follows. Presently defined values Identifier field identifies the semantics associated with the
for this field are specified in RFC1700 (see the Address Family Network Layer Reachability Information (NLRI) that follows.
Numbers section).
Subsequent Address Family Identifier: Presently defined values for the Address Family Identifier
field are specified in RFC1700 (see the Address Family Numbers
section).
This field provides additional information about the type of Subsequent Address Family Identifier (SAFI):
the Network Layer Reachability Information carried in the
attribute.
Withdrawn Routes: This field in combination with the Address Family Identifier
field identifies the semantics associated with the Network
Layer Reachability Information (NLRI) that follows.
Withdrawn Routes Network Layer Reachability Information:
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. The semantics of NLRI is
Family Identifier field is set to one of the values defined in identified by a combination of <AFI, SAFI> carried in the
this document, each NLRI is encoded as specified in the "NLRI attribute.
encoding" section of this document.
When the Subsequent Address Family Identifier field is set to
one of the values defined in this document, each NLRI is
encoded as specified in the "NLRI 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.
7. 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:
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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.
11. IANA Considerations 11. IANA Considerations
As specified in this document, the MPL_REACH_NLRI and MP_UNREACH_NLRI As specified in this document, the MP_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 this document. 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 and 2 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.
 End of changes. 

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