MPLS Working Group G. Mirsky
Internet-Draft J. Tantsura
Intended status: Standards Track Ericsson
Expires: February 9, 2016 I. Varlashkin
Google
M. Chen
Huawei
August 8, 2015
Bidirectional Forwarding Detection (BFD) Directed Return Path
draft-mirsky-mpls-bfd-directed-04
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
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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. Static and RSVP-TE sub-TLVs . . . . . . . . . . . . . 5
3.1.3. Segment Routing Tunnel sub-TLV . . . . . . . . . . . 5
3.2. Case of IPv6 Data Plane . . . . . . . . . . . . . . . . . 6
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.2. Sub-TLV . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.3. Return Codes . . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
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.
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This document defines the extension to LSP Ping [RFC4379], BFD
Reverse Path TLV, and proposes that it to be used to instruct the
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 detection of a failure on the reverse path cannot reliably be
interpreted as bi-directional defect and thus trigger, for
example, protection switchover of the forward direction;
o if a failure of the reverse path had been ignored, the ingress
node would not receive indication of forward direction failure
from its egress peer.
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To address these challenges the egress BFD peer should be instructed
to use specific path for its control packets.
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
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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
TLV, then only the first sub-TLV MUST be used and the rest MUST be
silently discarded.
If the egress LSR cannot find path specified in the Reverse Path TLV
it MUST send Echo Reply with the received Reverse Path TLV and set
the return code to "Failed to establish the BFD session. The
specified reverse path was not found" Section 3.4. The egress LSR
MAY establish the BFD session over IP network according to [RFC5884].
3.1.2. Static and RSVP-TE sub-TLVs
When explicit path on MPLS data plane set either as Static or RSVP-TE
LSP respective sub-TLVs defined in [RFC7110] identify explicit return
path.
3.1.3. Segment Routing Tunnel sub-TLV
In addition to Static and RSVP-TE, Segment Routing with MPLS data
plane can be used to set explicit path. In this 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 Entry 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Entry 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Entry N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 egress LSR MUST use the Value field as label stack for BFD
control packets for the BFD session identified by source IP address
and value in BFD Discriminator TLV.
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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. 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 data plane 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, i.e. ingress LSR, MAY include FECs corresponding to some
or all of segments imposed in the label stack by the ingress LSR to
communicate the segments traversed. "
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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 ingress LSR. Operationally
such restriction would not cause any problem or uncertainty as LSP
ping with FECs corresponding to some or all segments or traceroute
MAY precede 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). 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" MUST be sent back to the ingress LSR .
(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 foobar-1 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 foobar-2
[I-D.ietf-bfd-rfc5884-clarifications] 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
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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.
+----------+----------------------+---------------+
| 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
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6. Security Considerations
Security considerations discussed in [RFC5880], [RFC5884], and
[RFC4379], apply to this document.
7. Acknowledgements
8. Normative References
[I-D.ietf-bfd-rfc5884-clarifications]
Govindan, V., Rajaraman, K., Mirsky, G., Akiya, N., and S.
Aldrin, "Clarifications to RFC 5884", draft-ietf-bfd-
rfc5884-clarifications-02 (work in progress), June 2015.
[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-04 (work
in progress), July 2015.
[]
Previdi, S., Filsfils, C., Field, B., Leung, I., Vyncke,
E., and D. Lebrun, "IPv6 Segment Routing Header (SRH)",
draft-previdi-6man-segment-routing-header-07 (work in
progress), July 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379,
DOI 10.17487/RFC4379, February 2006,
<http://www.rfc-editor.org/info/rfc4379>.
[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
"MPLS Generic Associated Channel", RFC 5586,
DOI 10.17487/RFC5586, June 2009,
<http://www.rfc-editor.org/info/rfc5586>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<http://www.rfc-editor.org/info/rfc5880>.
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[RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
DOI 10.17487/RFC5881, June 2010,
<http://www.rfc-editor.org/info/rfc5881>.
[RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883,
June 2010, <http://www.rfc-editor.org/info/rfc5883>.
[RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
"Bidirectional Forwarding Detection (BFD) for MPLS Label
Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884,
June 2010, <http://www.rfc-editor.org/info/rfc5884>.
[RFC7110] Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord,
"Return Path Specified Label Switched Path (LSP) Ping",
RFC 7110, DOI 10.17487/RFC7110, January 2014,
<http://www.rfc-editor.org/info/rfc7110>.
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
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