Network Working Group Gargi Nalawade
Internet Draft Ruchi Kapoor
Expires: April 2005 Dan Tappan
Cisco Systems
Tunnel SAFI
draft-nalawade-kapoor-tunnel-safi-02.txt
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Abstract
There is a need for Tunnel end-point discovery within and across
Autonomous Systems. BGP is the only protocol that is widely-spoken
across Autonomous Systems and can carry this information. This
document defines how BGP speakers can convey Tunnel end-point
reachability information.
1. Introduction
Two end-points of a Tunnel need to know the end-point information and
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its binding to a network address at the remote point. Normally, this
can be statically shared and configured. But in case of a large
network where there may be a need for a large number of tunnels, the
number of tunnel end-points that need to be exchanged and maintained,
grows. It then needs to be exchanged and maintained using an inter-AS
protocol.
2. The Tunnel SAFI
This document defines a new SAFI called the Tunnel SAFI. The <AFI,
SAFI> [IANA-AFI] [IANA-SAFI] value pair used to identify this SAFI is
(AFI=1, SAFI=TBD) for the IPv4 AFI and (AFI=2, SAFI=TBD) for the IPv6
AFI.
For BGP Speakers supporting [BGP-4], the tunnel end point address
will be carried as an NLRI in the MP_REACH attribute for this SAFI.
For BGP Speakers suppprting [BGP-UPDATEv2], the tunnel end point
address will be carried as an NLRI in the NLRI section of the BGP
Updatev2 message.
The NLRI will be encoded as a 2-octet Identifier followed by the NLRI
format as specified by the respective AFI. The Identifier will
contain a 2-octet Identifier that identifies the Tunnel end point
being advertised. This Identifier enables multiple Tunnel end-points
to share the same network address, thus conserving the number of
addresses needed to be configured by the operator on each of the
Tunnel-endpoints.
3. BGP Attribute
The BGP SSA Attribute [BGP-SSA] will be used to carry the Tunnel
end-point information.
The Value Field of the BGP SSA Attribute, MUST contain at least one
of the following valid Type codes for this SAFI. It MAY contain one
or more TLVs with these Type codes.
Type 1: L2TPv3 Tunnel information
Type 2: mGRE Tunnel information
Type 3: IPSec Tunnel information
Type 4: MPLS Tunnel information
3.1. L2TPv3 Tunnel information TLV
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The L2TPv3 Tunnel Information TLV has a type of 1. The value part of
the L2TPv3 Tunnel Information Type contains the following :
- Preference (2 Octets)
- Flags (1 Octet)
- Cookie Length (1 Octet)
- Session ID (4 Octets)
- Cookie (Variable)
The L2TPv3 Tunnel Information TLV looks as follows :
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0x01 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length (2 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference (2 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| Flags | Cookie Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID (4 Octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Cookie (Variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where
Length A 2 Octet field that specifies the length of the L2TPv3
attribute in octets. The value contained in this Length field MUST
not exceed the total length of the BGP SSA [BGP-SSA] Attribute minus
the total length of any prior TLVs.
Preference A 2 Octet field containing a Preference associated with
the TLV. The Preference value indicates a preferred ordering of
tunneling encapsulations according to the sender. The recipient of
the information SHOULD take the sender's preference into account in
selecting which encapsulation it will use. A higher value indicates a
higher preference.
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Flags A 1 Octet field containing flag-bits. The leftmost bit
indicates whether Sequence numbering is to be used or not. The
remaining bits are reserved for future use.
Cookie Length Cookie Length is a 1 Octet field that contains the
length of the Variable length Cookie.
Session ID A 4 Octet field containing a non-zero identifier for a
session.
Cookie Cookie is a variable length (maximum 64 bits), value used by
L2TPv3 to check the association of a received data message with the
session identified by the Session ID.
The default value of the Length Field for the L2TPv3 Tunnel
information TLV is between 8 and 16 bytes, depending on the length of
the Cookie field specified in Cookie length. If the length of the TLV
is greater than that value, the subsequent portion of the Value field
contains one or more sub-TLVs.
A Sub-TLV when present is of the following format :
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value (Variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where Sub-Type & Length are of 1-Octet each & the Value field is
variable as specified by the Length.
3.2. mGRE Tunnel Information TLV
The mGRE Tunnel Information Type has a Type 2. The value part of the
mGRE Tunnel Information Type contains the following :
- Preference (2 Oc
tets)
- Flags (1 Octet)
- mGRE Key (0 or 4 Octets)
The mGRE Tunnel Information TLV looks as follows :
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0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0x02 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length (2 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference (2 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|K| Flags | |
+-+-+-+-+-+-+-+-+ |
| mGRE Key (4 Octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Length A 2 Octet field that specifies the length of the mGRE
information in octets. The value contained in this Length field MUST
not exceed the total length of the BGP SSA [BGP-SSA] Attribute minus
the total length of any prior TLVs.
Preference A 2 Octet field containing a Preference associated with
the TLV. The Preference value indicates a preferred ordering of
tunneling encapsulations according to the sender. The recipient of
the information SHOULD take the sender's preference into account in
selecting which encapsulation it will use. A higher value indicates a
higher preference.
Flags A 1 Octet field containing flag-bits. The leftmost bit
indicates whether Sequence numbering is to be used or not. The 2nd
bit indicates whether an mGRE Key is present or not. The remaining
bits are reserved for future use.
mGRE Key A 4 Octet field containing an optional mGRE Key.
If the Length field of the TLV contains a value greater than 3 Octets
plus the value specified in the Key Length, the subsequent portion of
the Value field contains one or more sub-TLVs.
A Sub-TLV when present is of the following format :
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Sub-Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value (Variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where Sub-Type & Length are of 1-Octet each & the Value field is
variable as specified by the Length.
3.3. IPSec Tunnel Information TLV
The IPSec Tunnel Information Type has a Type 3. The format of the
IPSec Tunnel Information TLV is TBD.
3.4. MPLS TLV
The MPLS TLV has a Type 4. The format of the MPLS TLV is TBD.
4. Capability Advertisement
A BGP speaker that wishes to exchange the IPv4-Tunnel SAFI, MUST use
the MP_EXT Capability Code as defined in [BGP-MP], to advertise the
corresponding (AFI, SAFI) pair.
A BGP speaker MAY participate in the distribution of IPv4-Tunnel
information.
5. Operation
A BGP Speaker that receives the Capability for the IPv4-Tunnel or
IPv6-Tunnel SAFI, MAY advertise the IPv4-Tunnel or IPv6-Tunnel
prefixes to that peer respectively.
In the UPDATE message for this SAFI sent to a peer, a BGP speaker
MUST only advertise the SAFI-specific attribute [BGP-SSA] TLVs that
are defined as valid for this SAFI.
If a BGP Speaker receives an SSA TLV that it does not recognize, it
will accept it and propagate it to other peers.
6. Deployment Considerations
In order for the Tunnels to come up between two end-points, the BGP
Speakers advertising the Tunnel end-points using the Ipv4 Tunnel
SAFI, MUST exchange at least one common encapsulation option.
7. Security Considerations
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This extension to BGP does not change the underlying security issues.
8. Acknowledgements
We would like to thank Jim Guichard, Arjun Sreekantiah, Shyam Suri,
Chandrashekhar Appanna, John Scudder and Mark Townsley for their
comments and suggestions.
9. References
[IANA-AFI] http://www.iana.org/assignments/address-family-numbers
[IANA-SAFI] http://www.iana.org/assignments/safi-namespace
[BGP-4] Rekhter, Y. and T. Li (editors), "A Border Gateway Protocol
4 (BGP-4)", Internet Draft draft-ietf-idr-bgp4-22.txt, February 2004.
[BGP-CAP] Chandra, R., Scudder, J., "Capabilities Advertisement with
BGP-4", draft-ietf-idr-rfc2842bis-02.txt, April 2002.
[BGP-SSA] Kapoor R., Nalawade G., "BGPv4 SAFI-Specific Attribute",
draft-nalawade-kapoor-bgp-ssa-02.txt, work in progress.
[MULTI-BGP] Bates et al, "Multiprotocol Extensions for BGP-4", draft-
ietf-idr-rfc2858bis-02.txt, work in progress.
[BGP-UPDATEv2] Nalawade G.et al, "BGPv4 Update-v2 Message", draft-
nalawade-bgp-update-v2-01.txt, work in progress.
10. Authors' Addresses
Gargi Nalawade
Cisco Systems, Inc
170 West Tasman Drive
San Jose, CA 95134
mailto:gargi@cisco.com
Ruchi Kapoor
Cisco Systems, Inc
170 West Tasman Drive
San Jose, CA 95134
mailto:ruchi@cisco.com
Dan Tappan
Cisco Systems, Inc
170 West Tasman Drive
San Jose, CA 95134
mailto:tappan@cisco.com
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13. Expiratio
n Date
This memo is filed as <draft-nalawade-kapoor-tunnel-safi-02.txt>, and
expires April, 2004.
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