| Internet Engineering Task Force | V. Govindan |
| Internet-Draft | N. Akiya |
| Intended status: Standards Track | Cisco Systems |
| Expires: January 5, 2015 | July 4, 2014 |
Label Switched Path (LSP) Ping Extended Bidirectional Forwarding Detection (BFD) Discriminator TLV
draft-vgovindan-mpls-extended-bfd-disc-tlv-00
This document defines an extended Bidirectional Forwarding Detection (BFD) discriminator TLV for the Multiprotocol Label Switching (MPLS) Label Switched Path (LSP) Ping mechanism, to allow bootstrapping of multiple BFD sessions for a given FEC.
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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Bidirectional Forwarding Detection (BFD) [RFC5880] for Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs), [RFC5884], describes a mechanism to use BFD to monitor the connectivity in-band on the LSPs. The BFD session on the LSP egress is bootstrapped using the LSP Ping mechanism, defined in [RFC4379], carrying the BFD Discriminator TLV that describes the BFD discriminator of the BFD session on the LSP ingress.
The BFD Discriminator TLV and defined procedures around this TLV only allow one BFD session to be bootstrapped per <MPLS Forwarding Equivalent Class (FEC), LSP> There are scenarios where an LSP ingress may desire to run multiple BFD sessions to monitor the connectivity on an LSP. To achieve the bootstrapping of multiple BFD sessions per FEC, a new TLV and procedures are required. Two scenarios where this is useful are described below:
An LSR ingress wanting to bootstrap one or more BFD sessions on an LSP is to include the Extended BFD Discriminator TLV, described in Section 4, in the MPLS echo request message for the FEC. The Extended BFD Discriminator TLV is capable of carrying multiple BFD discriminators, and each BFD discriminator is accompanied with an an instance identifier. The LSR egress, upon reception of this MPLS echo request, is to create requested number of BFD sessions for the specified FEC. Each BFD session object created on the LSR ingress and the LSR egress MUST be annotated with corresponding instance identifier. BFD session procedures are to follow those described in [RFC5884].
There are at least two options possible here:
[RFC5884] does not specify an explicit procedure for deleting BFD sessions. A few options are possible here:
Regardless of the option chosen to proceed, all BFD sessions established with the FEC MUST be removed automatically if the FEC is removed.
The Extended BFD Discriminator object is a new TLV that MAY be included in the MPLS echo request message. An MPLS echo request MUST NOT include more than one Extended BFD Discriminator object. The Extended BFD Discriminator object describes one or more BFD discriminators along with each having an instance identifier. An MPLS echo reply MAY include the Extended BFD Discriminator object, but MUST NOT include more than one Extended BFD Discriminator object.
Extended BFD Discriminator TLV Type is TBD1. Length is 8 or multiples of 8. Length of (8 x N) implies that there are N entries in the Value field of the Extended BFD Discriminator TLV. Each entry in the Value field of the Extended BFD Discriminator TLV has following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Instance Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BFD Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Extended BFD Discriminator TLV
See
The BFD Discriminator TLV and the Extended BFD Discriminator TLV are mutually exclusive. An MPLS echo request/reply message MUST NOT include both the BFD Discriminator TLV and the Extended BFD Discriminator TLV. Reception of an MPLS echo request with both the BFD Discriminator TLV and the Extended BFD Discriminator TLV is to result in the Return Code being set to Malformed echo request received (1).
If an LSP ingress wishes to bootstrap multiple BFD sessions with the Extended BFD Discriminator TLV when an LSP already has a BFD session bootstrapped with the BFD Discriminator TLV, following procedures are RECOMMENDED.
The LSP ingress is to send an MPLS echo request carrying the Extended BFD Discriminator TLV with the same BFD discriminator of the existing BFD session (one bootstrapped previously with the BFD Discriminator TLV), giving it an instance identifier. Once the transition of the existing BFD session is completed, then the LSP ingress can generate further MPLS echo request messages with the Extended BFD Discriminator TLV to bootstrap more BFD sessions.
The encapsulation of BFD packets are the same as specified by [RFC5884]
This document defines a mechanism to bootstrap multiple BFD sessions per FEC. BFD sessions, naturally, use system and network resources. More BFD sessions means more resources will be used. It is highly important to ensure only minimum number of BFD sessions are provisioned per FEC, and bootstrapped BFD sessions are properly deleted when no longer required. Additionally security measures described in [RFC4379] and [RFC5884] are to be followed.
The IANA is requested to assign new value TBD1 for Extended BFD Discriminator TLV from the "Multiprotocol Label Switching Architecture (MPLS) Label Switched Paths (LSPs) Ping Parameters - TLVs" registry.
Value Meaning Reference ----- ------- --------- TBD1 Extended BFD Discriminator TLV this document
TBD
Girija Rao
Cisco Systems
Email: giraghav@cisco.com
Mallik Mudigonda
Cisco Systems
Email: mmudigon@cisco.com
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC4379] | Kompella, K. and G. Swallow, "Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures", RFC 4379, February 2006. |
| [RFC5880] | Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD)", RFC 5880, June 2010. |
| [RFC5884] | Aggarwal, R., Kompella, K., Nadeau, T. and G. Swallow, "Bidirectional Forwarding Detection (BFD) for MPLS Label Switched Paths (LSPs)", RFC 5884, June 2010. |
The BFD Extended TLV can be used to carry the Operation Type and the Operation Status (Op Status) bits that are defined below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Operation Type| Op Status | Instance Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BFD Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Alternate format of the Extended
BFD Discriminator TLV
The Extended BFD Discriminator TLV in an MPLS echo request MUST have either Create(1) or Delete(2) operation type. The Extended BFD Discriminator TLV in an MPLS echo reply MUST have either CreateAck(3) or DeleteACK(4) operation type.