draft-ietf-bfd-seamless-base-01.txt   draft-ietf-bfd-seamless-base-02.txt 
Internet Engineering Task Force N. Akiya Internet Engineering Task Force N. Akiya
Internet-Draft C. Pignataro Internet-Draft C. Pignataro
Updates: 5880 (if approved) D. Ward Updates: 5880 (if approved) D. Ward
Intended status: Standards Track Cisco Systems Intended status: Standards Track Cisco Systems
Expires: December 28, 2014 M. Bhatia Expires: February 2, 2015 M. Bhatia
Ionos Networks Ionos Networks
P. K. Santosh P. K. Santosh
Juniper Networks Juniper Networks
June 26, 2014 August 1, 2014
Seamless Bidirectional Forwarding Detection (S-BFD) Seamless Bidirectional Forwarding Detection (S-BFD)
draft-ietf-bfd-seamless-base-01 draft-ietf-bfd-seamless-base-02
Abstract Abstract
This document defines a simplified mechanism to use Bidirectional This document defines a simplified mechanism to use Bidirectional
Forwarding Detection (BFD) with large portions of negotiation aspects Forwarding Detection (BFD) with large portions of negotiation aspects
eliminated, thus providing benefits such as quick provisioning as eliminated, thus providing benefits such as quick provisioning as
well as improved control and flexibility to network nodes initiating well as improved control and flexibility to network nodes initiating
the path monitoring. the path monitoring.
This document updates RFC5880. This document updates RFC5880.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 28, 2014. This Internet-Draft will expire on February 2, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Seamless BFD Overview . . . . . . . . . . . . . . . . . . . . 4 3. Seamless BFD Overview . . . . . . . . . . . . . . . . . . . . 4
4. S-BFD UDP Port . . . . . . . . . . . . . . . . . . . . . . . 5 4. S-BFD Discriminators . . . . . . . . . . . . . . . . . . . . 5
5. S-BFD Discriminators . . . . . . . . . . . . . . . . . . . . 5 4.1. Discriminator Pools . . . . . . . . . . . . . . . . . . . 5
6. Reflector BFD Session . . . . . . . . . . . . . . . . . . . . 6 4.2. S-BFD Discriminator Uniqueness . . . . . . . . . . . . . 6
7. State Variables . . . . . . . . . . . . . . . . . . . . . . . 7 5. Reflector BFD Session . . . . . . . . . . . . . . . . . . . . 7
7.1. New State Variables . . . . . . . . . . . . . . . . . . . 7 6. State Variables . . . . . . . . . . . . . . . . . . . . . . . 7
7.2. State Variable Initialization and Maintenance . . . . . . 7 6.1. New State Variables . . . . . . . . . . . . . . . . . . . 7
8. S-BFD Procedures . . . . . . . . . . . . . . . . . . . . . . 7 6.2. State Variable Initialization and Maintenance . . . . . . 8
8.1. Initiator Procedures . . . . . . . . . . . . . . . . . . 7 7. S-BFD Procedures . . . . . . . . . . . . . . . . . . . . . . 8
8.1.1. SBFDInitiator State Machine . . . . . . . . . . . . . 8 7.1. S-BFD Packet Demultiplexing . . . . . . . . . . . . . . . 8
8.1.2. Details of S-BFD Packet Sent by SBFDInitiator . . . . 9 7.2. Initiator Procedures . . . . . . . . . . . . . . . . . . 8
8.2. Responder Procedures . . . . . . . . . . . . . . . . . . 9 7.2.1. SBFDInitiator State Machine . . . . . . . . . . . . . 9
8.2.1. Responder Demultiplexing . . . . . . . . . . . . . . 10 7.2.2. Details of S-BFD Packet Sent by SBFDInitiator . . . . 10
8.2.2. Details of S-BFD Packet Sent by SBFDReflector . . . . 10 7.3. Responder Procedures . . . . . . . . . . . . . . . . . . 10
8.3. Diagnostic Values . . . . . . . . . . . . . . . . . . . . 10 7.3.1. Responder Demultiplexing . . . . . . . . . . . . . . 10
8.4. The Poll Sequence . . . . . . . . . . . . . . . . . . . . 11 7.3.2. Details of S-BFD Packet Sent by SBFDReflector . . . . 11
8.5. Control Plane Independent (C) . . . . . . . . . . . . . . 11 7.4. Diagnostic Values . . . . . . . . . . . . . . . . . . . . 11
8.6. Additional SBFDInitiator Behaviors . . . . . . . . . . . 11 7.5. The Poll Sequence . . . . . . . . . . . . . . . . . . . . 11
8.7. Additional SBFDReflector Behaviors . . . . . . . . . . . 12 7.6. Control Plane Independent (C) . . . . . . . . . . . . . . 11
9. Scaling Aspect . . . . . . . . . . . . . . . . . . . . . . . 12 7.7. Additional SBFDInitiator Behaviors . . . . . . . . . . . 12
10. Co-existence with Traditional BFD . . . . . . . . . . . . . . 12 7.8. Additional SBFDReflector Behaviors . . . . . . . . . . . 12
11. BFD Echo . . . . . . . . . . . . . . . . . . . . . . . . . . 12 8. Scaling Aspect . . . . . . . . . . . . . . . . . . . . . . . 13
12. Security Considerations . . . . . . . . . . . . . . . . . . . 13 9. Co-existence with Classical BFD Sessions . . . . . . . . . . 13
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 10. S-BFD Echo Function . . . . . . . . . . . . . . . . . . . . . 13
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 11. Security Considerations . . . . . . . . . . . . . . . . . . . 14
15. Contributing Authors . . . . . . . . . . . . . . . . . . . . 14 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
16.1. Normative References . . . . . . . . . . . . . . . . . . 15 14. Contributing Authors . . . . . . . . . . . . . . . . . . . . 15
16.2. Informative References . . . . . . . . . . . . . . . . . 15 15. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
15.1. Normative References . . . . . . . . . . . . . . . . . . 16
15.2. Informative References . . . . . . . . . . . . . . . . . 16
Appendix A. Loop Problem . . . . . . . . . . . . . . . . . . . . 16 Appendix A. Loop Problem . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction 1. Introduction
Bidirectional Forwarding Detection (BFD), [RFC5880] and related Bidirectional Forwarding Detection (BFD), [RFC5880] and related
documents, has efficiently generalized the failure detection documents, has efficiently generalized the failure detection
mechanism for multiple protocols and applications. There are some mechanism for multiple protocols and applications. There are some
improvements which can be made to better fit existing technologies. improvements which can be made to better fit existing technologies.
There is a possibility of evolving BFD to better fit new There is a possibility of evolving BFD to better fit new
technologies. This document focuses on several aspects of BFD in technologies. This document focuses on several aspects of BFD in
order to further improve efficiency, to expand failure detection order to further improve efficiency, to expand failure detection
coverage and to allow BFD usage for wider scenarios. This document coverage and to allow BFD usage for wider scenarios. This document
extends BFD to provide solutions to use cases listed in extends BFD to provide solutions to use cases listed in
[I-D.ietf-bfd-seamless-use-case]. [I-D.ietf-bfd-seamless-use-case].
One key aspect of the mechanism described in this document eliminates One key aspect of the mechanism described in this document eliminates
the time between a network node wanting to perform a connectivity the time between a network node wanting to perform a continuity test
test and completing the connectivity test. In traditional BFD terms, and completing the continuity test. In traditional BFD terms, the
the initial state changes from DOWN to UP is virtually nonexistent. initial state changes from DOWN to UP are virtually nonexistent.
Removal of this seam (i.e. time delay) in BFD provides applications a Removal of this seam (i.e. time delay) in BFD provides applications a
smooth and continuous operational experience. Therefore, "Seamless smooth and continuous operational experience. Therefore, "Seamless
BFD" (S-BFD) has been chosen as the name for this mechanism. BFD" (S-BFD) has been chosen as the name for this mechanism.
2. Terminology 2. Terminology
The reader is expected to be familiar with the BFD, IP and MPLS The reader is expected to be familiar with the BFD, IP and MPLS
terminologies and protocol constructs. This section describes terminologies and protocol constructs. This section describes
several new terminologies introduced by S-BFD. several new terminologies introduced by S-BFD.
o Classical BFD - BFD session types based on [RFC5880].
o S-BFD - Seamless BFD. o S-BFD - Seamless BFD.
o S-BFD packet - a BFD control packet on the well-known S-BFD port. o S-BFD packet - a BFD control packet destined to or sourced from
the well-known S-BFD port.
o Entity - a function on a network node that S-BFD mechanism allows o Entity - a function on a network node that S-BFD mechanism allows
remote network nodes to perform connectivity test to. An entity remote network nodes to perform continuity test to. An entity can
can be abstract (ex: reachability) or specific (ex: IP addresses, be abstract (ex: reachability) or specific (ex: IP addresses,
router-IDs, functions). router-IDs, functions).
o SBFDInitiator - an S-BFD session on a network node that performs a o SBFDInitiator - an S-BFD session on a network node that performs a
connectivity test to a remote entity by sending S-BFD packets. continuity test to a remote entity by sending S-BFD packets.
o SBFDReflector - an S-BFD session on a network node that listens o SBFDReflector - an S-BFD session on a network node that listens
for incoming S-BFD packets to local entities and generates for incoming S-BFD packets to local entities and generates
response S-BFD packets. response S-BFD packets.
o Reflector BFD session - synonymous with SBFDReflector. o Reflector BFD session - synonymous with SBFDReflector.
o S-BFD discriminator - a BFD discriminator allocated for a local o S-BFD discriminator - a BFD discriminator allocated for a local
entity and is being listened by an SBFDReflector. entity and is being listened by an SBFDReflector.
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session. Allocated S-BFD discriminators may be advertised by session. Allocated S-BFD discriminators may be advertised by
applications (ex: OSPF/IS-IS). Required result is that applications, applications (ex: OSPF/IS-IS). Required result is that applications,
on other network nodes, possess the knowledge of the mapping from on other network nodes, possess the knowledge of the mapping from
remote entities to S-BFD discriminators. The reflector BFD session remote entities to S-BFD discriminators. The reflector BFD session
is to, upon receiving an S-BFD packet targeted to one of local S-BFD is to, upon receiving an S-BFD packet targeted to one of local S-BFD
discriminator values, transmit a response S-BFD packet back to the discriminator values, transmit a response S-BFD packet back to the
initiator. initiator.
Once above setup is complete, any network nodes, having the knowledge Once above setup is complete, any network nodes, having the knowledge
of the mapping from a remote entity to an S-BFD discriminator, can of the mapping from a remote entity to an S-BFD discriminator, can
quickly perform a connectivity test to the remote entity by simply quickly perform a continuity test to the remote entity by simply
sending S-BFD packets with corresponding S-BFD discriminator value in sending S-BFD packets with corresponding S-BFD discriminator value in
the "your discriminator" field. the "your discriminator" field.
For example: For example:
<------- IS-IS Network -------> <------- IS-IS Network ------->
+---------+ +---------+
| | | |
A---------B---------C---------D A---------B---------C---------D
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BFD Discrim BFD Discrim BFD Discrim BFD Discrim
123 456 123 456
Figure 2: S-BFD for IS-IS Network Figure 2: S-BFD for IS-IS Network
The IS-IS with SystemID xxx (node A) allocates an S-BFD discriminator The IS-IS with SystemID xxx (node A) allocates an S-BFD discriminator
123, and advertises the S-BFD discriminator 123 in an IS-IS TLV. The 123, and advertises the S-BFD discriminator 123 in an IS-IS TLV. The
IS-IS with SystemID yyy (node D) allocates an S-BFD discriminator IS-IS with SystemID yyy (node D) allocates an S-BFD discriminator
456, and advertises the S-BFD discriminator 456 in an IS-IS TLV. A 456, and advertises the S-BFD discriminator 456 in an IS-IS TLV. A
reflector BFD session is created on both network nodes (node A and reflector BFD session is created on both network nodes (node A and
node D). When network node A wants to check the connectivity to node D). When network node A wants to check the reachability to
network node D, node A can send an S-BFD packet, destined to node D, network node D, node A can send an S-BFD packet, destined to node D,
with "your discriminator" field set to 456. When the reflector BFD with "your discriminator" field set to 456. When the reflector BFD
session on node D receives this S-BFD packet, then response S-BFD session on node D receives this S-BFD packet, then response S-BFD
packet is sent back to node A, which allows node A to complete the packet is sent back to node A, which allows node A to complete the
connectivity test. continuity test.
4. S-BFD UDP Port 4. S-BFD Discriminators
S-BFD functions on a well-known UDP port: TBD1. 4.1. Discriminator Pools
5. S-BFD Discriminators This document defines following suggestions for discriminator
management on SBFDInitiator and SBFDReflector sessions, to minimize
the collision between required S-BFD discriminators on a local
device.
Locally allocated S-BFD discriminator values for entities may be o SBFDInitiator is to allocate a discriminator from the BFD
arbitrary allocated or derived from values provided by applications. discriminator pool. If the system also supports classical BFD
These values may be protocol IDs (ex: System-ID, Router-ID) or that runs on [RFC5880], then the BFD discriminator pool SHOULD be
network targets (ex: IP address). To minimize the collision of shared by SBFDInitiator sessions and classical BFD sessions.
discriminator values between BFD and S-BFD, it is RECOMMENDED that
discriminator pool be separate for BFD and S-BFD. Even when o SBFDReflector is to allocate a discriminator from the S-BFD
employing the separate discriminator pool approach, collision is discriminator pool. The S-BFD discriminator pool SHOULD be a
still possible between one S-BFD application to another S-BFD separate pool than the BFD discriminator pool.
application, that may be using different values and algorithms to
derive S-BFD discriminator values. If the two applications are using Remainder of this subsection describes the reasons for above
S-BFD for a same purpose (ex: network reachability), then the suggestions.
Locally allocated S-BFD discriminator values for entities, listened
by SBFDReflector sessions, may be arbitrary allocated or derived from
values provided by applications. These values may be protocol IDs
(ex: System-ID, Router-ID) or network targets (ex: IP address). To
avoid derived S-BFD discriminator values already being assigned to
other BFD sessions (i.e. SBFDInitiator sessions and classical BFD
sessions), it is RECOMMENDED that discriminator pool for
SBFDReflector sessions be separate from other BFD sessions.
Even when following the separate discriminator pool approach,
collision is still possible between one S-BFD application to another
S-BFD application, that may be using different values and algorithms
to derive S-BFD discriminator values. If the two applications are
using S-BFD for a same purpose (ex: network reachability), then the
colliding S-BFD discriminator value can be shared. If the two colliding S-BFD discriminator value can be shared. If the two
applications are using S-BFD for a different purpose, then the applications are using S-BFD for a different purpose, then the
collision must be addressed. How such collisions are addressed is collision must be addressed. How such collisions are addressed is
outside the scope of this document. outside the scope of this document.
4.2. S-BFD Discriminator Uniqueness
One important characteristics of an S-BFD discriminator is that it One important characteristics of an S-BFD discriminator is that it
MUST be unique within an administrative domain. If multiple network MUST be unique within an administrative domain. If multiple network
nodes allocated a same S-BFD discriminator value, then S-BFD packets nodes allocated a same S-BFD discriminator value, then S-BFD packets
falsely terminating on a wrong network node can result in a reflector falsely terminating on a wrong network node can result in a reflector
BFD session to generate a response back, due to "your discriminator" BFD session to generate a response back, due to "your discriminator"
matching. This is clearly not desirable. If only IP based S-BFD is matching. This is clearly not desirable. If only IP based S-BFD is
considered, then it is possible for the reflector BFD session to considered, then it is possible for the reflector BFD session to
require demultiplexing of incoming S-BFD packets with combination of require demultiplexing of incoming S-BFD packets with combination of
destination IP address and "your discriminator". Then S-BFD destination IP address and "your discriminator". Then S-BFD
discriminator only has to be unique within a local node. However, discriminator only has to be unique within a local node. However,
S-BFD is a generic mechanism defined to run on wide range of S-BFD is a generic mechanism defined to run on wide range of
environments: IP, MPLS, etc. For other transports like MPLS, because environments: IP, MPLS, etc. For other transports like MPLS, because
of the need to use non-routable IP destination address, it is not of the need to use non-routable IP destination address, it is not
possible for reflector BFD session to demultiplex using IP possible for reflector BFD session to demultiplex using IP
destination address. With PHP, there may not be any incoming label destination address. With PHP, there may not be any incoming label
stack to aid in demultiplexing either. Thus, S-BFD imposes a stack to aid in demultiplexing either. Thus, S-BFD imposes a
requirement that S-BFD discriminators MUST be unique within an requirement that S-BFD discriminators MUST be unique within an
administrative domain. administrative domain.
6. Reflector BFD Session 5. Reflector BFD Session
Each network node creates one or more reflector BFD sessions. This Each network node creates one or more reflector BFD sessions. This
reflector BFD session is a session which transmits S-BFD packets in reflector BFD session is a session which transmits S-BFD packets in
response to received S-BFD packets with "your discriminator" having response to received S-BFD packets with "your discriminator" having
S-BFD discriminators allocated for local entities. Specifically, S-BFD discriminators allocated for local entities. Specifically,
this reflector BFD session is to have following characteristics: this reflector BFD session is to have following characteristics:
o MUST NOT transmit any S-BFD packets based on local timer expiry. o MUST NOT transmit any S-BFD packets based on local timer expiry.
o MUST transmit an S-BFD packet in response to a received S-BFD o MUST transmit an S-BFD packet in response to a received S-BFD
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One reflector BFD session may be responsible for handling received One reflector BFD session may be responsible for handling received
S-BFD packets targeted to all locally allocated S-BFD discriminators, S-BFD packets targeted to all locally allocated S-BFD discriminators,
or few reflector BFD sessions may each be responsible for subset of or few reflector BFD sessions may each be responsible for subset of
locally allocated S-BFD discriminators. This policy is a local locally allocated S-BFD discriminators. This policy is a local
matter, and is outside the scope of this document. matter, and is outside the scope of this document.
Note that incoming S-BFD packets may be IPv4, IPv6 or MPLS based. Note that incoming S-BFD packets may be IPv4, IPv6 or MPLS based.
How such S-BFD packets reach an appropriate reflector BFD session is How such S-BFD packets reach an appropriate reflector BFD session is
also a local matter, and is outside the scope of this document. also a local matter, and is outside the scope of this document.
7. State Variables 6. State Variables
S-BFD introduces new state variables, and modifies the usage of S-BFD introduces new state variables, and modifies the usage of
existing ones. existing ones.
7.1. New State Variables 6.1. New State Variables
A new state variable is added to the base specification in support of A new state variable is added to the base specification in support of
S-BFD. S-BFD.
o bfd.SessionType: The type of this session. Allowable values are: o bfd.SessionType: The type of this session. Allowable values are:
* SBFDInitiator - an S-BFD session on a network node that * SBFDInitiator - an S-BFD session on a network node that
performs a connectivity test to a target entity by sending performs a continuity test to a target entity by sending S-BFD
S-BFD packets. packets.
* SBFDReflector - an S-BFD session on a network node that listens * SBFDReflector - an S-BFD session on a network node that listens
for incoming S-BFD packets to local entities and generates for incoming S-BFD packets to local entities and generates
response S-BFD packets. response S-BFD packets.
bfd.SessionType variable MUST be initialized to the appropriate type bfd.SessionType variable MUST be initialized to the appropriate type
when an S-BFD session is created. when an S-BFD session is created.
7.2. State Variable Initialization and Maintenance 6.2. State Variable Initialization and Maintenance
Some state variables defined in section 6.8.1 of the BFD base Some state variables defined in section 6.8.1 of the BFD base
specification need to be initialized or manipulated differently specification need to be initialized or manipulated differently
depending on the session type. Ed-Note: Anything else?. depending on the session type.
o bfd.DemandMode: This variable MUST be initialized to 1 for session o bfd.DemandMode: This variable MUST be initialized to 1 for session
type SBFDInitiator, and MUST be initialized to 0 for session type type SBFDInitiator, and MUST be initialized to 0 for session type
SBFDReflector. SBFDReflector.
8. S-BFD Procedures 7. S-BFD Procedures
8.1. Initiator Procedures 7.1. S-BFD Packet Demultiplexing
Received BFD control packet MUST first be demultiplexed with
information from the lower layer (ex: destination UDP port,
associated channel type). If the packet is determined to be for an
SBFDReflector, then the packet MUST be looked up to locate a
corresponding SBFDReflector session based on the value from the "your
discriminator" field in the table describing S-BFD discriminators.
If the packet is determined not to be for SBFDReflector, then the
packet MUST be looked up to locate a corresponding SBFDInitiator
session or classical BFD session based on the value from the "your
discriminator" field in the table describing BFD discriminators. If
the located session is a SBFDInitiator, then destination of the
packet (i.e. destination IP address) SHOULD be validated to be for
self.
Details of the initial BFD control packet demultiplexing are
described in relevant S-BFD data plane documents.
7.2. Initiator Procedures
S-BFD packets transmitted by an SBFDInitiator MUST set "your S-BFD packets transmitted by an SBFDInitiator MUST set "your
discriminator" field to an S-BFD discriminator corresponding to the discriminator" field to an S-BFD discriminator corresponding to the
remote entity. remote entity.
S-BFD packets transmitted by an SBFDInitiator MUST NOT set "my Every SBFDInitiator MUST have a locally unique "my discriminator"
discriminator" field to an S-BFD discriminator allocated for a local allocated from the BFD discriminator pool.
entity (and is being monitored by a local SBFDReflector). This is to
prevent incoming response S-BFD packets, from a remote SBFDReflector,
having "your discriminator" as a S-BFD discriminator of a local
entity. Every SBFDInitiator is to have a unique "my discriminator",
and SHOULD be allocated from the BFD discriminator pool if the
implementation employs the approach of having separate discriminator
pools for BFD and S-BFD.
Below ASCII art describes high level concept of connectivity test Below ASCII art describes high level concept of continuity test using
using S-BFD. R2 allocates XX as the S-BFD discriminator for its S-BFD. R2 allocates XX as the S-BFD discriminator for its network
network reachability purpose, and advertises XX to neighbors. ASCII reachability purpose, and advertises XX to neighbors. ASCII art
art shows R1 and R4 performing a connectivity test to R2. shows R1 and R4 performing a continuity test to R2.
+--- md=50/yd=XX (ping) ----+ +--- md=50/yd=XX (ping) ----+
| | | |
|+-- md=XX/yd=50 (pong) --+ | |+-- md=XX/yd=50 (pong) --+ |
|| | | || | |
|v | v |v | v
R1 ==================== R2[*] ========= R3 ========= R4 R1 ==================== R2[*] ========= R3 ========= R4
| ^ |^ | ^ |^
| | || | | ||
| +-- md=60/yd=XX (ping) --+| | +-- md=60/yd=XX (ping) --+|
| | | |
+---- md=XX/yd=60 (pong) ---+ +---- md=XX/yd=60 (pong) ---+
[*] Reflector BFD session on R2. [*] Reflector BFD session on R2.
=== Links connecting network nodes. === Links connecting network nodes.
--- S-BFD packet traversal. --- S-BFD packet traversal.
Figure 3: S-BFD Connectivity Test Figure 3: S-BFD Continuity Test
8.1.1. SBFDInitiator State Machine 7.2.1. SBFDInitiator State Machine
An SBFDInitiator may be a persistent session on the initiator with a An SBFDInitiator may be a persistent session on the initiator with a
timer for S-BFD packet transmissions. An SBFDInitiator may also be a timer for S-BFD packet transmissions (stateful SBFDInitiator). An
module, a script or a tool on the initiator that transmits one or SBFDInitiator may also be a module, a script or a tool on the
more S-BFD packets "when needed". For transient SBFDInitiators, the initiator that transmits one or more S-BFD packets "when needed"
BFD state machine described in [RFC5880] may not be applicable. For (stateless SBFDInitiator). For stateless SBFDInitiators, a complete
persistent SBFDInitiators, the states and the state machine described BFD state machine may not be applicable. For stateful
in [RFC5880] will function but are more than necessary. The SBFDInitiators, the states and the state machine described in
following diagram provides an optimized state machine for persistent [RFC5880] will not function due to SBFDReflector session only sending
SBFDInitiators. The notation on each arc represents the state of the UP and ADMINDOWN states (i.e. SBFDReflector session does not send
SBFDInitiator (as received in the State field in the S-BFD packet) or INIT state). The following diagram provides the RECOMMENDED state
indicates the expiration of the Detection Timer. machine for stateful SBFDInitiators. The notation on each arc
represents the state of the SBFDInitiator (as received in the State
field in the S-BFD packet) or indicates the expiration of the
Detection Timer.
+--+ +--+
ADMIN DOWN, | | ADMIN DOWN, | |
TIMER | V TIMER | V
+------+ UP +------+ +------+ UP +------+
| |-------------------->| |----+ | |-------------------->| |----+
| DOWN | | UP | | UP | DOWN | | UP | | UP
| |<--------------------| |<---+ | |<--------------------| |<---+
+------+ ADMIN DOWN, +------+ +------+ ADMIN DOWN, +------+
TIMER TIMER
Figure 4: SBFDInitiator FSM Figure 4: SBFDInitiator FSM
Note that the above state machine is different from the base BFD Note that the above state machine is different from the base BFD
specification[RFC5880]. This is because the Init state is no longer specification[RFC5880]. This is because the INIT state is no longer
applicable for the SBFDInitiator. Another important difference is applicable for the SBFDInitiator. Another important difference is
the transition of the state machine from the Down state to the Up the transition of the state machine from the DOWN state to the UP
state when a packet with State Up is received by the initiator. The state when a packet with State UP is received by the SBFDInitiator.
definitions of the states and the events have the same meaning as in The definitions of the states and the events have the same meaning as
the base BFD specification [RFC5880]. in the base BFD specification [RFC5880].
8.1.2. Details of S-BFD Packet Sent by SBFDInitiator 7.2.2. Details of S-BFD Packet Sent by SBFDInitiator
S-BFD packets sent by an SBFDInitiator is to have following contents: S-BFD packets sent by an SBFDInitiator is to have following contents:
o Well-known UDP destination port assigned for S-BFD.
o UDP source port as per described in [RFC5881], [RFC5883],
[RFC5884] and [RFC5885].
o "my discriminator" assigned by local node. o "my discriminator" assigned by local node.
o "your discriminator" corresponding to a remote entity. o "your discriminator" corresponding to a remote entity.
o "State" MUST be set to a value describing local state. o "State" MUST be set to a value describing local state.
o "Desired Min TX Interval" MUST be set to a value describing local o "Desired Min TX Interval" MUST be set to a value describing local
desired minimum transmit interval. desired minimum transmit interval.
o "Required Min RX Interval" MUST be zero. o "Required Min RX Interval" MUST be zero.
o "Required Min Echo RX Interval" SHOULD be zero. o "Required Min Echo RX Interval" SHOULD be zero.
o "Detection Multiplier" MUST be set to a value describing locally o "Detection Multiplier" MUST be set to a value describing locally
used multiplier value. used multiplier value.
o Demand (D) bit MUST be set. o Demand (D) bit MUST be set.
8.2. Responder Procedures 7.3. Responder Procedures
A network node which receives S-BFD packets transmitted by an A network node which receives S-BFD packets transmitted by an
initiator is referred as responder. The responder, upon reception of initiator is referred as responder. The responder, upon reception of
S-BFD packets, is to perform necessary relevant validations described S-BFD packets, is to perform necessary relevant validations described
in [RFC5880], [RFC5881], [RFC5883], [RFC5884] and [RFC5885]. in [RFC5880], [RFC5881], [RFC5883], [RFC5884] and [RFC5885].
8.2.1. Responder Demultiplexing 7.3.1. Responder Demultiplexing
A BFD control packet received by a resonder is considered an S-BFD When a responder receives an S-BFD packet, if the value in the "your
packet if the packet is on the well-known S-BFD port. When a
responder receives an S-BFD packet, if the value in the "your
discriminator" field is not one of S-BFD discriminators allocated for discriminator" field is not one of S-BFD discriminators allocated for
local entities, then this packet MUST NOT be considered for this local entities, then this packet MUST NOT be considered for this
mechanism. If the value in the "your discriminator" field is one of mechanism. If the value in the "your discriminator" field is one of
S-BFD discriminators allocated for local entities, then the packet is S-BFD discriminators allocated for local entities, then the packet is
determined to be handled by a reflector BFD session responsible for determined to be handled by a reflector BFD session responsible for
the S-BFD discriminator. If the packet was determined to be the S-BFD discriminator. If the packet was determined to be
processed further for this mechanism, then chosen reflector BFD processed further for this mechanism, then chosen reflector BFD
session is to transmit a response BFD control packet using procedures session is to transmit a response BFD control packet using procedures
described in Section 8.2.2, unless prohibited by local policies (ex: described in Section 7.3.2, unless prohibited by local policies (ex:
administrative, security, rate-limiter, etc). administrative, security, rate-limiter, etc).
8.2.2. Details of S-BFD Packet Sent by SBFDReflector 7.3.2. Details of S-BFD Packet Sent by SBFDReflector
S-BFD packets sent by an SBFDReflector is to have following contents: S-BFD packets sent by an SBFDReflector is to have following contents:
o Well-known UDP destination port assigned for S-BFD.
o UDP source port as described in [RFC5881], [RFC5883], [RFC5884]
and [RFC5885].
o "my discriminator" MUST be copied from received "your o "my discriminator" MUST be copied from received "your
discriminator". discriminator".
o "your discriminator" MUST be copied from received "my o "your discriminator" MUST be copied from received "my
discriminator". discriminator".
o "State" MUST be UP or ADMINDOWN. Clarification of reflector BFD o "State" MUST be UP or ADMINDOWN. Clarification of reflector BFD
session state is described in Section 8.7. session state is described in Section 7.8.
o "Desired Min TX Interval" MUST be copied from received "Desired o "Desired Min TX Interval" MUST be copied from received "Desired
Min TX Interval". Min TX Interval".
o "Required Min RX Interval" MUST be set to a value describing how o "Required Min RX Interval" MUST be set to a value describing how
many incoming control packets this reflector BFD session can many incoming control packets this reflector BFD session can
handle. Further details are described in Section 8.7. handle. Further details are described in Section 7.8.
o "Required Min Echo RX Interval" SHOULD be set to zero. o "Required Min Echo RX Interval" SHOULD be set to zero.
o "Detection Multiplier" MUST be copied from received "Detection o "Detection Multiplier" MUST be copied from received "Detection
Multiplier". Multiplier".
o Demand (D) bit MUST be cleared. o Demand (D) bit MUST be cleared.
8.3. Diagnostic Values 7.4. Diagnostic Values
Diagnostic value in both directions MAY be set to a certain value, to Diagnostic value in both directions MAY be set to a certain value, to
attempt to communicate further information to both ends. However, attempt to communicate further information to both ends. However,
details of such are outside the scope of this specification. details of such are outside the scope of this specification.
8.4. The Poll Sequence 7.5. The Poll Sequence
Poll sequence MAY be used in both directions. The Poll sequence MUST Poll sequence MAY be used in both directions. The Poll sequence MUST
operate in accordance with [RFC5880]. An SBFDReflector MAY use the operate in accordance with [RFC5880]. An SBFDReflector MAY use the
Poll sequence to slow down that rate at which S-BFD packets are Poll sequence to slow down that rate at which S-BFD packets are
generated from an SBFDInitiator. This is done by the SBFDReflector generated from an SBFDInitiator. This is done by the SBFDReflector
using procedures described in Section 8.7 and setting the Poll (P) using procedures described in Section 7.8 and setting the Poll (P)
bit in the reflected S-BFD packet. The SBFDInitiator is to then send bit in the reflected S-BFD packet. The SBFDInitiator is to then send
the next S-BFD packet with the Final (F) bit set. If an the next S-BFD packet with the Final (F) bit set. If an
SBFDReflector receives an S-BFD packet with Poll (P) bit set, then SBFDReflector receives an S-BFD packet with Poll (P) bit set, then
the SBFDReflector MUST respond with an S-BFD packet with Poll (P) bit the SBFDReflector MUST respond with an S-BFD packet with Poll (P) bit
cleared and Final (F) bit set. cleared and Final (F) bit set.
8.5. Control Plane Independent (C) 7.6. Control Plane Independent (C)
Control plane independent (C) bit for an SBFDInitiator sending S-BFD Control plane independent (C) bit for an SBFDInitiator sending S-BFD
packets to a reflector BFD session MUST work according to [RFC5880]. packets to a reflector BFD session MUST work according to [RFC5880].
Reflector BFD session also MUST work according to [RFC5880]. Reflector BFD session also MUST work according to [RFC5880].
Specifically, if reflector BFD session implementation does not share Specifically, if reflector BFD session implementation does not share
fate with control plane, then response S-BFD packets transmitted MUST fate with control plane, then response S-BFD packets transmitted MUST
have control plane independent (C) bit set. If reflector BFD session have control plane independent (C) bit set. If reflector BFD session
implementation shares fate with control plane, then response S-BFD implementation shares fate with control plane, then response S-BFD
packets transmitted MUST NOT have control plane independent (C) bit packets transmitted MUST NOT have control plane independent (C) bit
set. set.
8.6. Additional SBFDInitiator Behaviors 7.7. Additional SBFDInitiator Behaviors
o If the SBFDInitiator receives a valid S-BFD packet in response to o If the SBFDInitiator receives a valid S-BFD packet in response to
transmitted S-BFD packet to a remote entity, then the transmitted S-BFD packet to a remote entity, then the
SBFDInitiator SHOULD conclude that S-BFD packet reached the SBFDInitiator SHOULD conclude that S-BFD packet reached the
intended remote entity. intended remote entity.
o When a sufficient number of S-BFD packets have not arrived as they o When a sufficient number of S-BFD packets have not arrived as they
should, the SBFDInitiator SHOULD declare loss of connectivity to should, the SBFDInitiator SHOULD declare loss of reachability to
the remote entity. The criteria for declaring loss of the remote entity. The criteria for declaring loss of
connectivity and the action that would be triggered as a result reachability and the action that would be triggered as a result
are outside the scope of this document. are outside the scope of this document.
o Relating to above bullet item, it is critical for an o Relating to above bullet item, it is critical for an
implementation to understand the latency to/from the reflector BFD implementation to understand the latency to/from the reflector BFD
session on the responder. In other words, for very first S-BFD session on the responder. In other words, for very first S-BFD
packet transmitted by the SBFDInitiator, an implementation MUST packet transmitted by the SBFDInitiator, an implementation MUST
NOT expect response S-BFD packet to be received for time NOT expect response S-BFD packet to be received for time
equivalent to sum of latencies: initiator to responder and equivalent to sum of latencies: initiator to responder and
responder back to initiator. responder back to initiator.
o If the SBFDInitiator receives an S-BFD packet with Demand (D) bit o If the SBFDInitiator receives an S-BFD packet with Demand (D) bit
set, the packet MUST be discarded. set, the packet MUST be discarded.
8.7. Additional SBFDReflector Behaviors 7.8. Additional SBFDReflector Behaviors
o S-BFD packets transmitted by the SBFDReflector MUST have "Required o S-BFD packets transmitted by the SBFDReflector MUST have "Required
Min RX Interval" set to a value which expresses how many incoming Min RX Interval" set to a value which expresses how many incoming
S-BFD packets this SBFDReflector can handle. The SBFDReflector S-BFD packets this SBFDReflector can handle. The SBFDReflector
can control how fast SBFInitiators will be sending S-BFD packets can control how fast SBFInitiators will be sending S-BFD packets
to self by ensuring "Required Min RX Interval" indicates a value to self by ensuring "Required Min RX Interval" indicates a value
based on the current load. based on the current load.
o If the SBFDReflector wishes to communicate to some or all o If the SBFDReflector wishes to communicate to some or all
SBFDInitiators that monitored local entity is "temporarily out of SBFDInitiators that monitored local entity is "temporarily out of
service", then S-BFD packets with "state" set to ADMINDOWN are service", then S-BFD packets with "state" set to ADMINDOWN are
sent to those SBFDInitiators. The SBFDInitiators, upon reception sent to those SBFDInitiators. The SBFDInitiators, upon reception
of such packets, MUST NOT conclude loss of connectivity to of such packets, MUST NOT conclude loss of reachability to
corresponding remote entity, and MUST back off packet transmission corresponding remote entity, and MUST back off packet transmission
interval for the remote entity to an interval no faster than 1 interval for the remote entity to an interval no faster than 1
second. If the SBFDReflector is generating a response S-BFD second. If the SBFDReflector is generating a response S-BFD
packet for a local entity that is in service, then "state" in packet for a local entity that is in service, then "state" in
response BFD control packets MUST be set to UP. response BFD control packets MUST be set to UP.
o If an SBFDReflector receives an S-BFD packet with Demand (D) bit o If an SBFDReflector receives an S-BFD packet with Demand (D) bit
cleared, the packet MUST be discarded. cleared, the packet MUST be discarded.
9. Scaling Aspect 8. Scaling Aspect
This mechanism brings forth one noticeable difference in terms of This mechanism brings forth one noticeable difference in terms of
scaling aspect: number of SBFDReflector. This specification scaling aspect: number of SBFDReflector. This specification
eliminates the need for egress nodes to have fully active BFD eliminates the need for egress nodes to have fully active BFD
sessions when only one side desires to perform connectivity tests. sessions when only one side desires to perform continuity tests.
With introduction of reflector BFD concept, egress no longer is With introduction of reflector BFD concept, egress no longer is
required to create any active BFD session per path/LSP/function required to create any active BFD session per path/LSP/function
basis. Due to this, total number of BFD sessions in a network is basis. Due to this, total number of BFD sessions in a network is
reduced. reduced.
10. Co-existence with Traditional BFD 9. Co-existence with Classical BFD Sessions
This mechanism has no issues being deployed with traditional BFDs Initial packet demultiplexing requirement is described in
([RFC5881], [RFC5883], [RFC5884] and [RFC5885]) because S-BFD Section 7.1. Because of this, S-BFD mechanism can co-exist with
discriminators which allow this mechanism to function are explicitly classical BFD sessions.
reserved and separate UDP port values are used with S-BFD.
11. BFD Echo 10. S-BFD Echo Function
BFD echo is outside the scope of this document. The concept of the S-BFD Echo function is similar to the BFD Echo
function described in [RFC5880], packets are self-generated and self-
terminated after traversing a link/path. S-BFD echo packets are
expected to u-turn on the target node in the data plane and MUST NOT
be processed by any reflector BFD sessions on the target node.
12. Security Considerations When using the S-BFD Echo function, it is RECOMMENDED that:
Same security considerations as [RFC5880], [RFC5881], [RFC5883], o Both S-BFD packets (with BFD control header) and S-BFD echo
[RFC5884] and [RFC5885] apply to this document. packets (implementation specific) be sent.
Additionally, implementing the following measures will strengthen o Both S-BFD packets and S-BFD echo packets have the same semantics
security aspects of the mechanism described by this document. in the forward direction to reach the target node.
o Implementations MUST provide filtering capability based on source In other words, it is not preferable to send just S-BFD echo packets.
IP addresses of received S-BFD packets: [RFC2827]. There are two reason behind this suggestion:
o Implementations MUST NOT act on received S-BFD packets containing o S-BFD packets can verify reachability to intended target node,
Martian addresses as source IP addresses. which allows one to conclude that S-BFD echo packets are u-turning
on the expected target node.
o Implementations MUST ensure that response S-BFD packets generated o S-BFD packets can detect when the target node is going out of
to the initiator by the SBFDReflector have a reachable target (ex: service (i.e. via receiving back ADMINDOWN state).
destination IP address).
Implementations MAY set "Required Min Echo RX Interval" field to
indicate the rate which SBFDInitiator is sending S-BFD Echo packets
(in ping) or the rate which SBFDReflector wants SBFDInitiators to
send S-BFD Echo packets (in pong). However, this is likely more than
necessary for the S-BFD Echo function to operate. Therefore, it is
RECOMMENDED that "Required Min Echo RX Interval" field simply be set
to zero in both directions.
Additionally, following aspects are left as implementation details,
and are outside the scope of this document:
o Format of the S-BFD Echo packet (ex: data beyond UDP header).
o Procedures on when and how to use the S-BFD Echo function.
11. Security Considerations
Same security considerations as [RFC5880], [RFC5881], [RFC5883],
[RFC5884] and [RFC5885] apply to this document. Additionally,
implementing the following measures will strengthen security aspects
of the mechanism described by this document:
o SBFDInitiator MAY pick crypto sequence number based on o SBFDInitiator MAY pick crypto sequence number based on
authentication mode configured. authentication mode configured.
o SBFDReflector MUST NOT look at the crypto sequence number before o SBFDReflector MUST NOT look at the crypto sequence number before
accepting the packet. accepting the packet.
o SBFDReflector MAY look at the Key ID o SBFDReflector MAY look at the Key ID
[I-D.ietf-bfd-generic-crypto-auth] in the incoming packet and [I-D.ietf-bfd-generic-crypto-auth] in the incoming packet and
verify the authentication data. verify the authentication data.
skipping to change at page 14, line 10 skipping to change at page 15, line 14
o SBFDReflector are not susceptible to replay attacks as they always o SBFDReflector are not susceptible to replay attacks as they always
respond to S-BFD packets irrespective of the sequence number respond to S-BFD packets irrespective of the sequence number
carried. carried.
o An attacker cannot impersonate the responder since the o An attacker cannot impersonate the responder since the
SBFDInitiator will only accept S-BFD packets that come with the SBFDInitiator will only accept S-BFD packets that come with the
sequence number that it had originally used when sending the S-BFD sequence number that it had originally used when sending the S-BFD
packet. packet.
13. IANA Considerations 12. IANA Considerations
A new value TBD1 is requested from the "Service Name and Transport
Protocol Port Number Registry". The requested registry entry is:
Service Name (REQUIRED) No action is required by IANA for this document.
s-bfd
Transport Protocol(s) (REQUIRED)
udp
Assignee (REQUIRED)
IESG <iesg@ietf.org>
Contact (REQUIRED)
BFD Chairs <bfd-chairs@tools.ietf.org>
Description (REQUIRED)
Seamless Bidirectional Forwarding Detection (S-BFD)
Reference (REQUIRED)
draft-ietf-bfd-seamless-base
Port Number (OPTIONAL)
TBD1 (Requesting 7784)
14. Acknowledgements 13. Acknowledgements
Authors would like to thank Jeffrey Haas for performing thorough Authors would like to thank Jeffrey Haas, Greg Mirsky and Marc
reviews and providing number of suggestions. Authors would like to Binderberger for performing thorough reviews and providing number of
thank Girija Raghavendra Rao, Marc Binderberger, Les Ginsberg, suggestions. Authors would like to thank Girija Raghavendra Rao, Les
Srihari Raghavan, Vanitha Neelamegam and Vengada Prasad Govindan from Ginsberg, Srihari Raghavan, Vanitha Neelamegam and Vengada Prasad
Cisco Systems for providing valuable comments. Authors would also Govindan from Cisco Systems for providing valuable comments. Authors
like to thank John E. Drake for providing comments and suggestions. would also like to thank John E. Drake and Pablo Frank for providing
comments and suggestions.
15. Contributing Authors 14. Contributing Authors
Tarek Saad Tarek Saad
Cisco Systems Cisco Systems
Email: tsaad@cisco.com Email: tsaad@cisco.com
Siva Sivabalan Siva Sivabalan
Cisco Systems Cisco Systems
Email: msiva@cisco.com Email: msiva@cisco.com
Nagendra Kumar Nagendra Kumar
skipping to change at page 15, line 4 skipping to change at page 15, line 41
Cisco Systems Cisco Systems
Email: tsaad@cisco.com Email: tsaad@cisco.com
Siva Sivabalan Siva Sivabalan
Cisco Systems Cisco Systems
Email: msiva@cisco.com Email: msiva@cisco.com
Nagendra Kumar Nagendra Kumar
Cisco Systems Cisco Systems
Email: naikumar@cisco.com Email: naikumar@cisco.com
Mallik Mudigonda Mallik Mudigonda
Cisco Systems Cisco Systems
Email: mmudigon@cisco.com Email: mmudigon@cisco.com
Sam Aldrin Sam Aldrin
Huawei Technologies Huawei Technologies
Email: aldrin.ietf@gmail.com Email: aldrin.ietf@gmail.com
16. References 15. References
16.1. Normative References
[I-D.ietf-bfd-seamless-use-case] 15.1. Normative References
Aldrin, S., Bhatia, M., Mirsky, G., Kumar, N., and S.
Matsushima, "Seamless Bidirectional Forwarding Detection
(BFD) Use Case", draft-ietf-bfd-seamless-use-case-00 (work
in progress), June 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, June 2010. (BFD)", RFC 5880, June 2010.
[RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection [RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, June (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, June
2010. 2010.
[RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection [RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for Multihop Paths", RFC 5883, June 2010. (BFD) for Multihop Paths", RFC 5883, June 2010.
[RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, [RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
"Bidirectional Forwarding Detection (BFD) for MPLS Label "Bidirectional Forwarding Detection (BFD) for MPLS Label
Switched Paths (LSPs)", RFC 5884, June 2010. Switched Paths (LSPs)", RFC 5884, June 2010.
16.2. Informative References 15.2. Informative References
[I-D.ietf-bfd-generic-crypto-auth] [I-D.ietf-bfd-generic-crypto-auth]
Bhatia, M., Manral, V., Zhang, D., and M. Jethanandani, Bhatia, M., Manral, V., Zhang, D., and M. Jethanandani,
"BFD Generic Cryptographic Authentication", draft-ietf- "BFD Generic Cryptographic Authentication", draft-ietf-
bfd-generic-crypto-auth-06 (work in progress), April 2014. bfd-generic-crypto-auth-06 (work in progress), April 2014.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering: [I-D.ietf-bfd-seamless-use-case]
Defeating Denial of Service Attacks which employ IP Source Aldrin, S., Bhatia, M., Mirsky, G., Kumar, N., and S.
Address Spoofing", BCP 38, RFC 2827, May 2000. Matsushima, "Seamless Bidirectional Forwarding Detection
(BFD) Use Case", draft-ietf-bfd-seamless-use-case-00 (work
in progress), June 2014.
[RFC5885] Nadeau, T. and C. Pignataro, "Bidirectional Forwarding [RFC5885] Nadeau, T. and C. Pignataro, "Bidirectional Forwarding
Detection (BFD) for the Pseudowire Virtual Circuit Detection (BFD) for the Pseudowire Virtual Circuit
Connectivity Verification (VCCV)", RFC 5885, June 2010. Connectivity Verification (VCCV)", RFC 5885, June 2010.
Appendix A. Loop Problem Appendix A. Loop Problem
Consider a scenario where we have two nodes and both are S-BFD Consider a scenario where we have two nodes and both are S-BFD
capable. capable.
skipping to change at page 16, line 51 skipping to change at page 17, line 37
Solutions Solutions
The current proposals to avoid the loop problem are: The current proposals to avoid the loop problem are:
o Overload "D" bit (Demand mode bit): Initiator always sets the 'D' o Overload "D" bit (Demand mode bit): Initiator always sets the 'D'
bit and reflector clears it. This way we can identify if a bit and reflector clears it. This way we can identify if a
received packet was a reflected packet and avoid reflecting it received packet was a reflected packet and avoid reflecting it
back. However this changes the interpretation of 'D' bit. back. However this changes the interpretation of 'D' bit.
o Use of State field in the BFD control packets: Initiator will o Use of State field in the BFD control packets: Initiator will
always send packets with State set to "DOWN" and reflector will always send packets with State set to DOWN and reflector will send
send back packets with state field set to "UP. Reflectors will back packets with state field set to UP. Reflectors will never
never reflect any received packets with state as "UP". However reflect any received packets with state as UP. However the only
the only issue is the use of state field differently i.e. state in issue is the use of state field differently i.e. state in the
the S-BFD control packet from initiator does not reflect the local S-BFD control packet from initiator does not reflect the local
state which is anyway not significant at reflector. state which is anyway not significant at reflector.
o Use of local discriminator as My Disc at reflector: Reflector will o Use of local discriminator as My Disc at reflector: Reflector will
always fill in My Discriminator with a locally allocated always fill in My Discriminator with a locally allocated
discriminator value (not reserved discriminators) and will not discriminator value (not reserved discriminators) and will not
copy it from the received packet. copy it from the received packet.
Authors' Addresses Authors' Addresses
Nobo Akiya Nobo Akiya
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