Bidirectional Forwarding Detection (BFD) Directed Return Path
draft-mirsky-mpls-bfd-directed-00
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
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|---|---|---|---|
| Authors | Greg Mirsky , Jeff Tantsura , Ilya Varlashkin | ||
| Last updated | 2014-06-30 | ||
| Replaced by | draft-ietf-mpls-bfd-directed, draft-ietf-mpls-bfd-directed | ||
| RFC stream | (None) | ||
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| Consensus boilerplate | Unknown | ||
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draft-mirsky-mpls-bfd-directed-00
MPLS Working Group G. Mirsky
Internet-Draft J. Tantsura
Intended status: Standards Track Ericsson
Expires: January 1, 2015 I. Varlashkin
EasyNet
June 30, 2014
Bidirectional Forwarding Detection (BFD) Directed Return Path
draft-mirsky-mpls-bfd-directed-00
Abstract
Bidirectional Forwarding Detection (BFD) is expected to monitor bi-
directional paths. When forward direction of a BFD session is to
monitor explicitly routed path there is\ a need to be able to direct
far-end BFD peer to use specific path as reverse direction of the BFD
session.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 1, 2015.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . 3
1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3
1.1.2. Requirements Language . . . . . . . . . . . . . . . . 3
2. Problem Satement . . . . . . . . . . . . . . . . . . . . . . 3
3. Direct Reverse BFD Path . . . . . . . . . . . . . . . . . . . 3
3.1. Case of MPLS Data Plane . . . . . . . . . . . . . . . . . 4
3.1.1. BFD Reverse Path TLV . . . . . . . . . . . . . . . . 4
3.1.2. Segment Routing Tunnel sub-TLV . . . . . . . . . . . 4
3.2. Case of IPv6 Data Plane . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
4.1. TLV . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
7. Normative References . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
The [RFC5880], [RFC5881], and the [RFC5883] established BFD protocol
for IP networks and the [RFC5884] set rules of using BFD Asynchronous
mode over IP/MPLS LSPs. All standards implicitly assume that the
far-end BFD peer will use the best route regardless of route being
used to send BFD control packets towards it. As result, if the near-
end BFD peer sends its BFD control packets over explicit path that is
diverging from the best route, then reverse direction of the BFD
session is likely not to be on co-routed bi-directional path with the
forward direction of the BFD session. And because BFD control
packets are not guaranteed to cross the same links and nodes in both
directions detection of Loss of Continuity (LoC) defect in forward
direction is not guaranteed or free of positive negatives.
This document proposes to use BFD Return Path TLV extension to LSP
Ping [RFC4379] to instruct the far-end BFD peer to use explicit path
for its BFD control packets associated with the particular BFD
session. As a special case, forward and reverse directions of the
BFD session can form bi-directional co-routed associated channel.
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1.1. Conventions used in this document
1.1.1. Terminology
BFD: Bidirectional Forwarding Detection
MPLS: Multiprotocol Label Switching
LSP: Label Switching Path
LoC: Loss of Continuity
1.1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
2. Problem Satement
BFD is best suited to monitor bi-directional co-routed paths. In
most cases, in IP and IP/MPLS networks the best route between two IP
nodes is likely to be co-routed in the stable network environment so
that implicit BF D requirement is being fulfilled. If BFD is tasked
to monitor unidirectional explicitly routed path, e.g. MPLS LSP, its
control packets in forward direction would be in-band due to
mechanism defined in [RFC5884] and [RFC5586]. But the reverse
direction of the BFD session would still follow the best route and
that presents following problems in regard to detecting defects on
the unidirectional explicit path:
- failure detection on the reverse path cannot be interpreted as
bi-directional failure and thus trigger, for example, protection
switchover of the forward direction;
- if reverse direction is in Down state, the head-end node would
not receive indication of forward direction failure from its far-
end peer.
To address these challenges the far-end BFD peer should be instructed
to use specific path for its control packets.
3. Direct Reverse BFD Path
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3.1. Case of MPLS Data Plane
LSP ping, defined in [RFC4379], uses BFD Discriminator TLV [RFC5884]
to bootstrap a BFD session over an MPLS LSP. This document defines a
new TLV, BFD Reverse Path TLV, that must contain a single sub-TLV
that can be used to carry information about reverse path for the
specified in BFD Discriminator TLV session.
3.1.1. BFD Reverse Path TLV
The BFD Reverse Path TLV is an optional TLV within the LSP ping
protocol. However, if used the BFD Discriminator TLV MUST be
included in an Echo Request message as well. If the BFD
Discriminator TLV is not present when the BFD Reverse Path TLV is
included, then it MUST be treated as malformed Echo Request, as
described in [RFC4379].
The BFD Reverse Path TLV carries the specified path that BFD control
packets of the BFD session referenced in the BFD Discriminator TLV
are required to follow. The format of the BFD Reverse Path TLV is as
presented in Figure 1.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BFD Reverse Path TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reverse Path |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: BFD Reverse Path TLV
BFD Reverse Path TLV Type is 2 octets in length and value to be
assigned by IANA.
Length is 2 octets in lengh and defines the length in octets of the
Reverse Path field.
3.1.2. Segment Routing Tunnel sub-TLV
With MPLS data plane explicit path can be either Static or RSVP-TE
LSP, or Segment Routing tunnel. In case of Static or RSVP-TE LSP
[RFC7110] defined sub-TLVs to identify explicit return path. For the
Segment Routing with MPLS data plane case a new sub-TLV is defined in
this document as presented in Figure 2.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SegRouting MPLS sub-TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Stack Element |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Stack Element |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Segment Routing MPLS Tunnel sub-TLV
The Segment Routing Tunnel sub-TLV Type is two octets in length, and
will be allocated by IANA.
The Segment Routing Tunnel sub-TLV MAY be used in Reply Path TLV
defined in [RFC7110]
3.2. Case of IPv6 Data Plane
IPv6 can be data plane of choice for Segment Routed tunnels
[I-D.previdi-6man-segment-routing-header]. In such networks the BFD
Reverse Path TLV described in Section 3.1.1 can be used as well. IP
networks, unlike IP/MPLS, do not require use of LSP ping with BFD
Discriminator TLV[RFC4379] to bootstrap BFD session. But to specify
reverse path of a BFD session in IPv6 environment the BFD
Discriminator TLV MUST be used along with the BFD Reverse Path TLV.
The BFD Reverse Path TLV in IPv6 network MUST include sub-TLV.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SegRouting IPv6 sub-TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 Prefix |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 Prefix |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Segment Routing IPv6 Tunnel sub-TLV
4. IANA Considerations
4.1. TLV
The IANA is requested to assign a new value for BFD Reverse Path TLV
from the "Multiprotocol Label Switching Architecture (MPLS) Label
Switched Paths (LSPs) Ping Parameters - TLVs" registry, "TLVs and
sub-TLVs" sub-registry.
+----------+----------------------+---------------+
| Value | Description | Reference |
+----------+----------------------+---------------+
| X (TBD1) | BFD Reverse Path TLV | This document |
+----------+----------------------+---------------+
Table 1: New BFD Reverse Type TLV
4.2. Sub-TLV
The IANA is requested to assign one new sub-TLV type from
"Multiprotocol Label Switching Architecture (MPLS) Label Switched
Paths (LSPs) Ping Parameters - TLVs" registry, "Sub-TLVs for TLV Type
1" sub-registry.
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+----------+-------------------------------------+---------------+
| Value | Description | Reference |
+----------+-------------------------------------+---------------+
| X (TBD2) | Segment Routing MPLS Tunnel sub-TLV | This document |
| X (TBD3) | Segment Routing IPv6 Tunnel sub-TLV | This document |
+----------+-------------------------------------+---------------+
Table 2: New Segment Routing Tunnel sub-TLV
5. Security Considerations
Sequirity considerations discussed in [RFC5880], [RFC5884], and
[RFC4379], apply to this document.
6. Acknowledgements
7. Normative References
[I-D.previdi-6man-segment-routing-header]
Previdi, S., Filsfils, C., Field, B., and I. Leung, "IPv6
Segment Routing Header (SRH)", draft-previdi-6man-segment-
routing-header-01 (work in progress), June 2014.
[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.
[RFC5586] Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic
Associated Channel", RFC 5586, June 2009.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, June 2010.
[RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, June
2010.
[RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for Multihop Paths", RFC 5883, 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.
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[RFC7110] Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord,
"Return Path Specified Label Switched Path (LSP) Ping",
RFC 7110, January 2014.
Authors' Addresses
Greg Mirsky
Ericsson
Email: gregory.mirsky@ericsson.com
Jeff Tantsura
Ericsson
Email: jeff.tantsura@ericsson.com
Ilya Varlashkin
EasyNet
Email: Ilya.Varlashkin@easynet.com
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