MPLS Working Group G. Mirsky
Internet-Draft J. Tantsura
Intended status: Standards Track Ericsson
Expires: September 6, 2015 I. Varlashkin
Google
M. Chen
Huawei
March 5, 2015
Bidirectional Forwarding Detection (BFD) Directed Return Path
draft-mirsky-mpls-bfd-directed-03
Abstract
Bidirectional Forwarding Detection (BFD) is expected to monitor bi-
directional paths. When a BFD session monitors in its forward
direction an explicitly routed path there is a need to be able to
direct egress BFD peer to use specific path as reverse direction of
the BFD session.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 6, 2015.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
Mirsky, et al. Expires September 6, 2015 [Page 1]
Internet-Draft BFD Directed Return Path March 2015
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
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 Statement . . . . . . . . . . . . . . . . . . . . . . 3
3. Direct Reverse BFD Path . . . . . . . . . . . . . . . . . . . 4
3.1. Case of MPLS Data Plane . . . . . . . . . . . . . . . . . 4
3.1.1. BFD Reverse Path TLV . . . . . . . . . . . . . . . . 4
3.1.2. Segment Routing Tunnel sub-TLV . . . . . . . . . . . 5
3.2. Case of IPv6 Data Plane . . . . . . . . . . . . . . . . . 5
3.3. Bootstrapping BFD session with BFD Reverse Path over
Segment Routed tunnel . . . . . . . . . . . . . . . . . . 6
3.4. Return Codes . . . . . . . . . . . . . . . . . . . . . . 7
4. Use Case Scenario . . . . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
5.1. TLV . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.2. Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.3. Return Codes . . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
8. Normative References . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
RFC 5880 [RFC5880], RFC 5881 [RFC5881], and RFC 5883 [RFC5883]
established the BFD protocol for IP networks and RFC 5884 [RFC5884]
set rules of using BFD asynchronous mode over IP/MPLS LSPs. All
standards implicitly assume that the egress BFD peer will use the
shortest path route regardless of route being used to send BFD
control packets towards it. As result, if the ingress 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 may demonstrate
positive negatives.
This document defines the extension to LSP Ping [RFC4379], BFD
Reverse Path TLV, and proposes that it to be used to instruct the
Mirsky, et al. Expires September 6, 2015 [Page 2]
Internet-Draft BFD Directed Return Path March 2015
egress BFD peer to use explicit path for its BFD control packets
associated with the particular BFD session. The TLV will be
allocated from the TLV and sub-TLV registry defined by RFC 4379
[RFC4379]. As a special case, forward and reverse directions of the
BFD session can form bi-directional co-routed associated channel.
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 Statement
BFD is best suited to monitor bi-directional co-routed paths. In
most cases, given stable environments, the forward and reverse
direction between two nodes is likely to be co-routed, this
fulfilling the implicit BFD requirements. If BFD is used to monitor
unidirectional explicitly routed paths, e.g. MPLS-TE LSPs, its
control packets in forward direction would be in-band using the
mechanism defined in [RFC5884] and [RFC5586]. But the reverse
direction of the BFD session would still follow the shortest path
route and that might lead to the following problems detecting
failures on the unidirectional explicit path:
o failure detection on the reverse path cannot be interpreted as bi-
directional failure and thus trigger, for example, protection
switchover of the forward direction;
o if reverse direction is in Down state, the head-end node would not
receive indication of forward direction failure from its egress
peer.
To address these challenges the egress BFD peer should be instructed
to use specific path for its control packets.
Mirsky, et al. Expires September 6, 2015 [Page 3]
Internet-Draft BFD Directed Return Path March 2015
3. Direct Reverse BFD Path
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 length and defines the length in octets of the
Reverse Path field.
Reverse Path field contains a sub-TLV. Any Target FEC sub-TLV,
already or in the future defined, from IANA sub-registry Sub-TLVs for
TLV Types 1, 16, and 21 of MPLS LSP Ping Parameters registry MAY be
used in this field. Only one sub-TLV MUST be included in the Reverse
Path TLV. If more than one sub-TLVs are present in the Reverse Path
Mirsky, et al. Expires September 6, 2015 [Page 4]
Internet-Draft BFD Directed Return Path March 2015
TLV, then only the first sub-TLV MUST be used and the rest MUST be
silently discarded.
If the egress LSR fails to establish the BFD session because path
specified in the Reverse Path TLV is not known, the egress MAY
establish the BFD session over IP network [RFC5884] and MAY send Echo
Reply with the Reverse Path TLV received and the return code set to
"Failed to establish the BFD session". The specified reverse path
was not found" (TBD4) Section 3.4. If the egress LSR cannot find
path specified in the Reverse Path TLV and does not establish BFD
session per RFC 5884, it MUST send Echo Reply with the Reverse Path
TLV received and the return code set to "Failed to establish the BFD
session. The specified reverse path was not found".
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.
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
Mirsky, et al. Expires September 6, 2015 [Page 5]
Internet-Draft BFD Directed Return Path March 2015
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.
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
3.3. Bootstrapping BFD session with BFD Reverse Path over Segment
Routed tunnel
As discussed in [I-D.kumarkini-mpls-spring-lsp-ping] introduction of
Segment Routing network domains with MPLS dataplane adds three new
sub-TLVs that may be used with Target FEC TLV. Section 6.1 addresses
use of new sub-TLVs in Target FEC TLV in LSP ping and LSP traceroute.
For the case of LSP ping the [I-D.kumarkini-mpls-spring-lsp-ping]
states that:
"Initiator MUST include FEC(s) corresponding to the destination
segment.
Initiator MAY include FECs corresponding to some or all of segments
imposed in the label stack by the initiator to communicate the
segments traversed. "
When LSP ping is used to bootstrap BFD session this document updates
this and defines that LSP Ping MUST include the FEC corresponding to
the destination segment and SHOULD NOT include FECs corresponding to
some or all of segment imposed by the initiator. Operationally such
restriction would not cause any problem or uncertainty as LSP ping
Mirsky, et al. Expires September 6, 2015 [Page 6]
Internet-Draft BFD Directed Return Path March 2015
with FECs corresponding to some or all segments or traceroute may
preceed the LSP ping that bootstraps the BFD session.
3.4. Return Codes
This document defines the following Return Codes:
o Failed to establish the BFD session. The specified reverse path
was not found, (TBD4) - the specified reverse path was not found,
failed to establish the BFD session. When a specified reverse
path is not available at the egress LSR, an Echo Reply with the
return code set to "Failed to establish the BFD session. The
specified reverse path was not found." MAY be sent back to the
initiator . (Section 3.1.1)
4. Use Case Scenario
In network presented in Figure 4 node A monitors two tunnels to node
H: A-B-C-D-G-H and A-B-E-F-G-H. To bootstrap BFD session to monitor
the first tunnel, node A MUST include BFD Discriminator TLV with
Discriminator value N and MAY include BFD Reverse Path TLV that
references H-G-D-C-B-A tunnel. To bootstrap BFD session to monitor
the second tunnel, node A MUST include BFD Discriminator TLV with
Discriminator value M and MAY include BFD Reverse Path TLV that
references H-G-F-E-B-A tunnel.
C---------D
| |
A-------B G-----H
| |
E---------F
Figure 4: Use Case for BFD Reverse Path TLV
If an operator needs node H to monitor path to node A, e.g.
H-G-D-C-B-A tunnel, then by looking up list of known Reverse Paths it
MAY find and use existing BFD sessions.
5. IANA Considerations
5.1. 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.
Mirsky, et al. Expires September 6, 2015 [Page 7]
Internet-Draft BFD Directed Return Path March 2015
+----------+----------------------+---------------+
| Value | Description | Reference |
+----------+----------------------+---------------+
| X (TBD1) | BFD Reverse Path TLV | This document |
+----------+----------------------+---------------+
Table 1: New BFD Reverse Type TLV
5.2. Sub-TLV
The IANA is requested to assign two new sub-TLV types from
"Multiprotocol Label Switching Architecture (MPLS) Label Switched
Paths (LSPs) Ping Parameters - TLVs" registry, "Sub-TLVs for TLV
Types 1, 16, and 21" sub-registry.
+----------+-------------------------------------+---------------+
| 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
5.3. Return Codes
The IANA is requested to assign a new Return Code value from the
"Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs)
Ping Parameters" registry, "Return Codes" sub-registry, as follows
using a Standards Action value.
+----------+----------------------------------------+---------------+
| Value | Description | Reference |
+----------+----------------------------------------+---------------+
| X (TBD4) | Failed to establish the BFD session. | This document |
| | The specified reverse path was not | |
| | found. | |
+----------+----------------------------------------+---------------+
Table 3: New Return Code
6. Security Considerations
Secuirity considerations discussed in [RFC5880], [RFC5884], and
[RFC4379], apply to this document.
Mirsky, et al. Expires September 6, 2015 [Page 8]
Internet-Draft BFD Directed Return Path March 2015
7. Acknowledgements
8. Normative References
[I-D.kumarkini-mpls-spring-lsp-ping]
Kumar, N., Swallow, G., Pignataro, C., Akiya, N., Kini,
S., Gredler, H., and M. Chen, "Label Switched Path (LSP)
Ping/Trace for Segment Routing Networks Using MPLS
Dataplane", draft-kumarkini-mpls-spring-lsp-ping-02 (work
in progress), October 2014.
[]
Previdi, S., Filsfils, C., Field, B., and I. Leung, "IPv6
Segment Routing Header (SRH)", draft-previdi-6man-segment-
routing-header-05 (work in progress), January 2015.
[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.
[RFC7110] Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord,
"Return Path Specified Label Switched Path (LSP) Ping",
RFC 7110, January 2014.
Mirsky, et al. Expires September 6, 2015 [Page 9]
Internet-Draft BFD Directed Return Path March 2015
Authors' Addresses
Greg Mirsky
Ericsson
Email: gregory.mirsky@ericsson.com
Jeff Tantsura
Ericsson
Email: jeff.tantsura@ericsson.com
Ilya Varlashkin
Google
Email: Ilya@nobulus.com
Mach(Guoyi) Chen
Huawei
Email: mach.chen@huawei.com
Mirsky, et al. Expires September 6, 2015 [Page 10]