draft-ietf-bfd-seamless-base-05.txt   draft-ietf-bfd-seamless-base-06.txt 
Internet Engineering Task Force N. Akiya Internet Engineering Task Force N. Akiya
Internet-Draft Big Switch Networks Internet-Draft Big Switch Networks
Updates: 5880 (if approved) C. Pignataro Updates: 5880 (if approved) C. Pignataro
Intended status: Standards Track D. Ward Intended status: Standards Track D. Ward
Expires: December 21, 2015 Cisco Systems Expires: August 12, 2016 Cisco Systems
M. Bhatia M. Bhatia
Ionos Networks Ionos Networks
S. Pallagatti S. Pallagatti
Juniper Networks February 9, 2016
June 19, 2015
Seamless Bidirectional Forwarding Detection (S-BFD) Seamless Bidirectional Forwarding Detection (S-BFD)
draft-ietf-bfd-seamless-base-05 draft-ietf-bfd-seamless-base-06
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.
skipping to change at page 1, line 48 skipping to change at page 1, line 47
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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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 21, 2015. This Internet-Draft will expire on August 12, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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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 . . . . . . . . . . . . . . . . . . . . 5
4. S-BFD Discriminators . . . . . . . . . . . . . . . . . . . . 5 4. S-BFD Discriminators . . . . . . . . . . . . . . . . . . . . 6
4.1. S-BFD Discriminator Uniqueness . . . . . . . . . . . . . 5 4.1. S-BFD Discriminator Uniqueness . . . . . . . . . . . . . 6
4.2. Discriminator Pools . . . . . . . . . . . . . . . . . . . 6 4.2. Discriminator Pools . . . . . . . . . . . . . . . . . . . 6
5. Reflector BFD Session . . . . . . . . . . . . . . . . . . . . 7 5. Reflector BFD Session . . . . . . . . . . . . . . . . . . . . 7
6. State Variables . . . . . . . . . . . . . . . . . . . . . . . 7 6. State Variables . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. New State Variables . . . . . . . . . . . . . . . . . . . 7 6.1. New State Variables . . . . . . . . . . . . . . . . . . . 7
6.2. State Variable Initialization and Maintenance . . . . . . 8 6.2. State Variable Initialization and Maintenance . . . . . . 8
7. S-BFD Procedures . . . . . . . . . . . . . . . . . . . . . . 8 7. S-BFD Procedures . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Demultiplexing of S-BFD Control Packet . . . . . . . . . 8 7.1. Demultiplexing of S-BFD Control Packet . . . . . . . . . 8
7.2. Initiator Procedures . . . . . . . . . . . . . . . . . . 9 7.2. Responder Procedures . . . . . . . . . . . . . . . . . . 9
7.2.1. SBFDInitiator State Machine . . . . . . . . . . . . . 10 7.2.1. Responder Demultiplexing . . . . . . . . . . . . . . 9
7.2.2. Transmission of S-BFD Control Packet by SBFDInitiator 10 7.2.2. Transmission of S-BFD Control Packet by SBFDReflector 9
7.3. Responder Procedures . . . . . . . . . . . . . . . . . . 12 7.2.3. Additional SBFDReflector Behaviors . . . . . . . . . 11
7.3.1. Responder Demultiplexing . . . . . . . . . . . . . . 12 7.3. Initiator Procedures . . . . . . . . . . . . . . . . . . 11
7.3.2. Transmission of S-BFD Control Packet by SBFDReflector 13 7.3.1. SBFDInitiator State Machine . . . . . . . . . . . . . 12
7.3.2. Transmission of S-BFD Control Packet by SBFDInitiator 13
7.3.3. Additional SBFDInitiator Behaviors . . . . . . . . . 13
7.4. Diagnostic Values . . . . . . . . . . . . . . . . . . . . 14 7.4. Diagnostic Values . . . . . . . . . . . . . . . . . . . . 14
7.5. The Poll Sequence . . . . . . . . . . . . . . . . . . . . 14 7.5. The Poll Sequence . . . . . . . . . . . . . . . . . . . . 14
7.6. Control Plane Independent (C) . . . . . . . . . . . . . . 15 8. Scaling Aspect . . . . . . . . . . . . . . . . . . . . . . . 14
7.7. Additional SBFDInitiator Behaviors . . . . . . . . . . . 15 9. Co-existence with Classical BFD Sessions . . . . . . . . . . 14
7.8. Additional SBFDReflector Behaviors . . . . . . . . . . . 15 10. S-BFD Echo Function . . . . . . . . . . . . . . . . . . . . . 15
8. Scaling Aspect . . . . . . . . . . . . . . . . . . . . . . . 16 11. Security Considerations . . . . . . . . . . . . . . . . . . . 15
9. Co-existence with Classical BFD Sessions . . . . . . . . . . 16 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
10. S-BFD Echo Function . . . . . . . . . . . . . . . . . . . . . 16 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16
11. Security Considerations . . . . . . . . . . . . . . . . . . . 17 14. Contributing Authors . . . . . . . . . . . . . . . . . . . . 17
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 15. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18 15.1. Normative References . . . . . . . . . . . . . . . . . . 17
14. Contributing Authors . . . . . . . . . . . . . . . . . . . . 18 15.2. Informative References . . . . . . . . . . . . . . . . . 17
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 Appendix A. Loop Problem . . . . . . . . . . . . . . . . . . . . 18
15.1. Normative References . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
15.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Loop Problem . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
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.
extends BFD to provide solutions to use cases listed in
[I-D.ietf-bfd-seamless-use-case]. Specifically, this document defines Seamless Bidirectional Forwarding
Detection (S-BFD) a simplified mechanism to use Bidirectional
Forwarding Detection (BFD) with large portions of negotiation aspects
eliminated, thus providing benefits such as quick provisioning as
well as improved control and flexibility to network nodes initiating
the path monitoring. S-BFD enables cases benefiting from the use of
core BFD technologies in a fashion that leverages existing
implementations and protocol machinery while providing a rather
simplified and largely stateless infrastructure for continuity
testing.
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 continuity test the time between a network node wanting to perform a continuity test
and completing the continuity test. In traditional BFD terms, the and completing the continuity test. In traditional BFD terms, the
initial state changes from DOWN to UP are virtually nonexistent. initial state changes from DOWN to UP are virtually nonexistent.
Removal of this seam (i.e., time delay) in BFD provides applications Removal of this seam (i.e., time delay) in BFD provides applications
a smooth and continuous operational experience. Therefore, "Seamless a 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 [RFC5880], IP
terminologies and protocol constructs. This section describes [RFC0791] [RFC2460] and MPLS [RFC3031] terminologies and protocol
several new terminologies introduced by S-BFD. constructs. This section describes several new terminologies
introduced by S-BFD.
o Classical BFD - BFD session types based on [RFC5880]. o Classical BFD - BFD session types based on [RFC5880].
o S-BFD - Seamless BFD. o S-BFD - Seamless BFD.
o S-BFD control packet - a BFD control packet for the S-BFD o S-BFD control packet - a BFD control packet for the S-BFD
mechanism. mechanism.
o S-BFD echo packet - a BFD echo packet for the S-BFD mechanism. o S-BFD echo packet - a BFD echo packet for the S-BFD mechanism.
skipping to change at page 4, line 50 skipping to change at page 5, line 12
Figure 1: S-BFD Terminology Relationship Figure 1: S-BFD Terminology Relationship
3. Seamless BFD Overview 3. Seamless BFD Overview
An S-BFD module on each network node allocates one or more S-BFD An S-BFD module on each network node allocates one or more S-BFD
discriminators for local entities, and creates a reflector BFD discriminators for local entities, and creates a reflector BFD
session. Allocated S-BFD discriminators may be advertised by session. Allocated S-BFD discriminators may be advertised by
applications (e.g., OSPF/IS-IS). Required result is that applications (e.g., OSPF/IS-IS). Required result is that
applications, on other network nodes, possess the knowledge of the applications, on other network nodes, possess the knowledge of the
mapping from remote entities to S-BFD discriminators. The reflector S-BFD discriminators allocated by a remote node to remote entities.
BFD session is to, upon receiving an S-BFD control packet targeted to The reflector BFD session is to, upon receiving an S-BFD control
one of local S-BFD discriminator values, transmit a response S-BFD packet targeted to one of local S-BFD discriminator values, transmit
control packet back to the initiator. a response S-BFD control packet back to the initiator.
Once above setup is complete, any network nodes, having the knowledge Once above setup is complete, any network node, having the knowledge
of the mapping from a remote entity to an S-BFD discriminator, can of the S-BFD discriminator allocated toby a remote node to remote
quickly perform a continuity test to the remote entity by simply entity/entities, it can quickly perform a continuity test to the
sending S-BFD control packets with corresponding S-BFD discriminator remote entity by simply sending S-BFD control packets with
value in the "your discriminator" field. corresponding S-BFD discriminator value in the "your discriminator"
field.
For example: For example:
<------- IS-IS Network -------> <------- IS-IS Network ------->
+---------+ +---------+
| | | |
A---------B---------C---------D A---------B---------C---------D
^ ^ ^ ^
| | | |
SystemID SystemID SystemID SystemID
xxx yyy xxx yyy
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 S-BFD module in a system IS-IS SystemID xxx (node A) allocates an
123, and advertises the S-BFD discriminator 123 in an IS-IS TLV. The S-BFD discriminator 123, and IS-IS will advertises the S-BFD
IS-IS with SystemID yyy (node D) allocates an S-BFD discriminator discriminator 123 in an IS-IS TLV. S-BFD module in a system with IS-
456, and advertises the S-BFD discriminator 456 in an IS-IS TLV. A IS SystemID yyy (node D) allocates an S-BFD discriminator 456, and
IS-IS 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 reachability to node D). When network node A wants to check the reachability to
network node D, node A can send an S-BFD control packet, destined to network node D, node A can send an S-BFD control packet, destined to
node D, with "your discriminator" field set to 456. When the node D, with "your discriminator" field set to 456. When the
reflector BFD session on node D receives this S-BFD control packet, reflector BFD session on node D receives this S-BFD control packet,
then response S-BFD control packet is sent back to node A, which then response S-BFD control packet is sent back to node A, which
allows node A to complete the continuity test. allows node A to complete the continuity test.
The use of multiple S-BFD discriminators by a single network node is
outside the scope of this document.
4. S-BFD Discriminators 4. S-BFD Discriminators
4.1. S-BFD Discriminator Uniqueness 4.1. 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 control nodes allocated a same S-BFD discriminator value, then S-BFD control
packets falsely terminating on a wrong network node can result in a packets falsely terminating on a wrong network node can result in a
reflector BFD session to generate a response back, due to "your reflector BFD session to generate a response back, due to "your
discriminator" matching. This is clearly not desirable. If only IP discriminator" matching. This is clearly not desirable.
based S-BFD is considered, then it is possible for the reflector BFD
session to require demultiplexing of incoming S-BFD control packets
with combination of destination IP address and "your discriminator".
Then S-BFD discriminator only has to be unique within a local node.
However, S-BFD is a generic mechanism defined to run on wide range of
environments: IP, MPLS, etc. For other transports like MPLS, because
of the need to use non-routable IP destination address, it is not
possible for reflector BFD session to demultiplex using IP
destination address. With PHP, there may not be any incoming label
stack to aid in demultiplexing either. Thus, S-BFD imposes a
requirement that S-BFD discriminators MUST be unique within an
administrative domain.
4.2. Discriminator Pools 4.2. Discriminator Pools
This subsection describes a discriminator pool implementation This subsection describes a discriminator pool implementation
technique to minimize S-BFD discriminator collisions. The result technique to minimize S-BFD discriminator collisions. The result
will allow an implementation to better satisfy the S-BFD will allow an implementation to better satisfy the S-BFD
discriminator uniqueness requirement defined in Section 4.1. discriminator uniqueness requirement defined in Section 4.1.
o SBFDInitiator is to allocate a discriminator from the BFD o SBFDInitiator is to allocate a discriminator from the BFD
discriminator pool. If the system also supports classical BFD discriminator pool. If the system also supports classical BFD
skipping to change at page 7, line 46 skipping to change at page 7, line 47
6. 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.
6.1. 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: This is a variable introduced by o bfd.SessionType: This is a variable introduced her and used by
[I-D.ietf-bfd-multipoint] and describes the type of this session. [I-D.ietf-bfd-multipoint], and describes the type of this session.
Allowable values for S-BFD sessions are: Allowable values for S-BFD sessions are:
* SBFDInitiator - an S-BFD session on a network node that * SBFDInitiator - an S-BFD session on a network node that
performs a continuity test to a target entity by sending S-BFD performs a continuity test to a target entity by sending 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 control packets to local entities and for incoming S-BFD control packets to local entities and
generates response S-BFD control packets. generates response S-BFD control 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.
6.2. 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 A state variable defined in Section 6.8.1 of [RFC5880] need to be
specification need to be initialized or manipulated differently initialized or manipulated differently depending on the session type.
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.
7. S-BFD Procedures 7. S-BFD Procedures
7.1. Demultiplexing of S-BFD Control Packet 7.1. Demultiplexing of S-BFD Control Packet
S-BFD packet MUST be demultiplexed with lower layer information S-BFD packet MUST be demultiplexed with lower layer information
skipping to change at page 8, line 49 skipping to change at page 8, line 48
Packet MUST be looked up to locate a corresponding Packet MUST be looked up to locate a corresponding
SBFDReflector session based on the value from the "your SBFDReflector session based on the value from the "your
discriminator" field in the table describing S-BFD discriminator" field in the table describing S-BFD
discriminators. discriminators.
Else Else
Packet MUST be looked up to locate a corresponding Packet MUST be looked up to locate a corresponding
SBFDInitiator session or classical BFD session based on the SBFDInitiator session or classical BFD session based on the
value from the "your discriminator" field in the table value from the "your discriminator" field in the table
describing BFD discriminators. describing BFD discriminators. If no match then received
packet MUST be discarded.
If session is SBFDInitiator If session is SBFDInitiator
Destination of the packet (i.e., destination IP address) Destination of the packet (i.e., destination IP address)
SHOULD be validated to be for self. SHOULD be validated to be for self.
Else Else
Packet MUST be discarded Packet MUST be discarded
Else Else
Procedure described in [RFC5880] MUST be applied. Procedure described in [RFC5880] MUST be applied.
More details on S-BFD control packet demultiplexing are described in More details on S-BFD control packet demultiplexing are described in
relevant S-BFD data plane documents. relevant S-BFD data plane documents.
7.2. Initiator Procedures 7.2. Responder Procedures
A network node which receives S-BFD control packets transmitted by an
initiator is referred as responder. The responder, upon reception of
S-BFD control packets, is to perform necessary relevant validations
described in [RFC5880].
7.2.1. Responder Demultiplexing
S-BFD packet MUST be demultiplexed with lower layer information
(e.g., dedicated destination UDP port, associated channel type).
Following procedure SHOULD be executed by responder:
If "your discriminator" not one of the entry allocated for local
entities
Packet MUST be discarded.
Else
Packet is determined to be handled by a reflector BFD session
responsible for that S-BFD discriminator.
If local policy allows (e.g., administrative, security, rate-
limiter, etc)
Chosen reflector BFD session SHOULD transmit a response BFD
control packet using procedures described in Section 7.3.2.
7.2.2. Transmission of S-BFD Control Packet by SBFDReflector
Contents of S-BFD control packets sent by an SBFDReflector MUST be
set as per Section 6.8.7 of [RFC5880]. There are few fields which
needs to be set differently from [RFC5880] as follows:
State (Sta)
Set to bfd.SessionState (either UP or ADMINDOWN only).
Clarification of reflector BFD session state is described in
Section 7.2.3.
Demand (D)
Set to 0.
Detect Mult
Value to be copied from "Detection Multiplier" filed of
received BFD packet.
My Discriminator
Value be copied from "your discriminator" filed of received BFD
packet.
Your Discriminator
Value be copied from "my discriminator" filed of received BFD
packet.
Desired Min TX Interval
Value be copied from "Desired Min TX Interval" filed of
received BFD packet.
Required Min RX Interval
Set to a bfd.RequiredMinRxInterval, value describing minimum
interval, in microseconds between received SBFD Control
packets. Further details are described in Section 7.2.3.
Required Min Echo RX Interval
If device supports looping back S-BFD echo packets
Set to the minimum required Echo packet receive interval for
this session.
Else
Set to 0.
7.2.3. Additional SBFDReflector Behaviors
o S-BFD control packets transmitted by the SBFDReflector MUST have
"Required Min RX Interval" set to a value which expresses, in
microseconds, the minimum interval between incoming S-BFD control
packets this SBFDReflector can handle. The SBFDReflector can
control how fast SBFInitiators will be sending S-BFD control
packets to self by ensuring "Required Min RX Interval" indicates a
value based on the current load.
o If the SBFDReflector wishes to communicate to some or all
SBFDInitiators that monitored local entity is "temporarily out of
service", then S-BFD control packets with "state" set to ADMINDOWN
are sent to those SBFDInitiators. The SBFDInitiators, upon
reception of such packets, MUST NOT conclude loss of reachability
to corresponding remote entity, and MUST back off packet
transmission interval for the remote entity to an interval no
faster than 1 second. If the SBFDReflector is generating a
response S-BFD control packet for a local entity that is in
service, then "state" in response BFD control packets MUST be set
to UP.
o If an SBFDReflector receives an S-BFD control packet with Demand
(D) bit cleared, the packet MUST be discarded.
7.3. Initiator Procedures
S-BFD control packets transmitted by an SBFDInitiator MUST set "your S-BFD control 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.
Every SBFDInitiator MUST have a locally unique "my discriminator" Every SBFDInitiator MUST have a locally unique "my discriminator"
allocated from the BFD discriminator pool. allocated from the BFD discriminator pool.
Below ASCII art describes high level concept of continuity test using Below Figure 3 art describes high level concept of continuity test
S-BFD. R2 allocates XX as the S-BFD discriminator for its network using S-BFD. R2 allocates XX as the S-BFD discriminator for its
reachability purpose, and advertises XX to neighbors. ASCII art network reachability purpose, and advertises XX to neighbors. ASCII
shows R1 and R4 performing a continuity test to R2. art 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 control packet traversal. --- S-BFD control packet traversal.
Figure 3: S-BFD Continuity Test Figure 3: S-BFD Continuity Test
7.2.1. SBFDInitiator State Machine 7.3.1. 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 control packet transmissions (stateful timer for S-BFD control packet transmissions (stateful
SBFDInitiator). An SBFDInitiator may also be a module, a script or a SBFDInitiator). An SBFDInitiator may also be a module, a script or a
tool on the initiator that transmits one or more S-BFD control tool on the initiator that transmits one or more S-BFD control
packets "when needed" (stateless SBFDInitiator). For stateless packets "when needed" (stateless SBFDInitiator). For stateless
SBFDInitiators, a complete BFD state machine may not be applicable. SBFDInitiators, a complete BFD state machine may not be applicable.
For stateful SBFDInitiators, the states and the state machine For stateful SBFDInitiators, the states and the state machine
described in [RFC5880] will not function due to SBFDReflector session described in [RFC5880] will not function due to SBFDReflector session
only sending UP and ADMINDOWN states (i.e., SBFDReflector session only sending UP and ADMINDOWN states (i.e., SBFDReflector session
skipping to change at page 10, line 42 skipping to change at page 13, line 13
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 SBFDInitiator. state when a packet with State UP is received by the SBFDInitiator.
The definitions of the states and the events have the same meaning as The definitions of the states and the events have the same meaning as
in the base BFD specification [RFC5880]. in the base BFD specification [RFC5880].
7.2.2. Transmission of S-BFD Control Packet by SBFDInitiator 7.3.2. Transmission of S-BFD Control Packet by SBFDInitiator
Contents of S-BFD control packets sent by an SBFDInitiator MUST be Contents of S-BFD control packets sent by an SBFDInitiator MUST be
set as follows: set as per Section 6.8.7 of [RFC5880]. There are few fields which
needs to be set differently from [RFC5880] as follows:
Version
Set to the current version number (1).
Diagnostic (Diag)
MAY be set to appropriate value for communicating with peer.
State (Sta)
Set to the value indicated by local state.
Poll (P)
Set to 1 if the local system is sending a Poll Sequence.
Final (F)
Set to 1 if the local system is responding to a Control packet
received with the Poll (P) bit set, or 0 if not.
Control Plane Independent (C)
Set to 1 if the local system's BFD implementation is
independent of the control plane (it can continue to function
through a disruption of the control plane.)
Authentication Present (A)
Set to 1 if authentication is in use on this session
(bfd.AuthType is nonzero), or 0 if not.
Demand (D)
MUST be set always.
Multipoint (M)
MUST be set to 0.
Detect Mult
MUST be set to a value describing locally used multiplier
value.
Length
Set to the appropriate length, based on the fixed header length
(24) plus any Authentication Section.
My Discriminator
Set to value assigned by local node.
Your Discriminator
Set to value corresponding to remote entity.
Desired Min TX Interval
MUST be set to a value describing local desired minimum
transmit interval.
Required Min RX Interval
MUST be set to 0.
Required Min Echo RX Interval
MUST be set to 0.
7.3. Responder Procedures
A network node which receives S-BFD control packets transmitted by an
initiator is referred as responder. The responder, upon reception of
S-BFD control packets, is to perform necessary relevant validations
described in [RFC5880], [RFC5881], [RFC5883], [RFC5884] and
[RFC5885].
7.3.1. Responder Demultiplexing
S-BFD packet MUST be demultiplexed with lower layer information
(e.g., dedicated destination UDP port, associated channel type).
Following procedure SHOULD be executed by responder:
If "your discriminator" not one of the entry allocated for local
entities
Packet MUST NOT be considered for this mechanism.
Else
Packet is determined to be handled by a reflector BFD session
responsible for that S-BFD discriminator.
If local policy allows (e.g., administrative, security, rate-
limiter, etc)
Chosen reflector BFD session SHOULD transmit a response BFD
control packet using procedures described in Section 7.3.2.
7.3.2. Transmission of S-BFD Control Packet by SBFDReflector
Contents of S-BFD control packets sent by an SBFDReflector MUST be
set as follows:
Version
Set to the current version number (1).
Diagnostic (Diag)
MAY be set to appropriate value for communicating with peer.
State (Sta)
MUST be set to UP or ADMINDOWN. Clarification of reflector BFD
session state is described in Section 7.8.
Poll (P)
Set to 1 if the local system is sending a Poll Sequence, or 0
if not.
Final (F)
Set to 1 if the local system is responding to a Control packet
received with the Poll (P) bit set, or 0 if not.
Control Plane Independent (C)
Set to 1 if the local system's BFD implementation is
independent of the control plane (it can continue to function
through a disruption of the control plane.)
Authentication Present (A)
Set to 1 if authentication is in use on this session
(bfd.AuthType is nonzero), or 0 if not.
Demand (D) Demand (D)
MUST be cleared. D bit is used to identify S-BFD packet originated from
SBFDInitiator and is always set to 1.
Multipoint (M)
MUST be set to 0.
Detect Mult
MUST be copied from received "Detection Multiplier".
Length
Set to the appropriate length, based on the fixed header length
(24) plus any Authentication Section.
My Discriminator
MUST be copied from received "your discriminator".
Your Discriminator Your Discriminator
MUST be copied from received "my discriminator". Set to bfd.RemoteDiscr. bfd.RemoteDiscr is set to discriminator
value of remote entity. It MAY be learnt from routing
Desired Min TX Interval protocols or configured locally.
MUST be copied from received "Desired Min TX Interval".
Required Min RX Interval Required Min RX Interval
MUST be set to a value describing how many incoming control Set to 0.
packets this reflector BFD session can handle. Further details
are described in Section 7.8.
Required Min Echo RX Interval Required Min Echo RX Interval
If device supports looping back S-BFD echo packets Set to 0.
MUST set non-zero value desired by local device.
Else
MUST be set to 0.
7.4. Diagnostic Values
Diagnostic value in both directions MAY be set to a certain value, to
attempt to communicate further information to both ends. However,
details of such are outside the scope of this specification.
7.5. The Poll Sequence
Poll sequence MAY be used in both directions. The Poll sequence MUST
operate in accordance with [RFC5880]. An SBFDReflector MAY use the
Poll sequence to slow down that rate at which S-BFD control packets
are generated from an SBFDInitiator. This is done by the
SBFDReflector using procedures described in Section 7.8 and setting
the Poll (P) bit in the reflected S-BFD control packet. The
SBFDInitiator is to then send the next S-BFD control packet with the
Final (F) bit set. If an SBFDReflector receives an S-BFD control
packet with Poll (P) bit set, then the SBFDReflector MUST respond
with an S-BFD control packet with Poll (P) bit cleared and Final (F)
bit set.
7.6. Control Plane Independent (C)
Control plane independent (C) bit for an SBFDInitiator sending S-BFD
control packets to a reflector BFD session MUST work according to
[RFC5880]. Reflector BFD session also MUST work according to
[RFC5880]. Specifically, if reflector BFD session implementation
does not share fate with control plane, then response S-BFD control
packets transmitted MUST have control plane independent (C) bit set.
If reflector BFD session implementation shares fate with control
plane, then response S-BFD control packets transmitted MUST NOT have
control plane independent (C) bit set.
7.7. Additional SBFDInitiator Behaviors 7.3.3. Additional SBFDInitiator Behaviors
o If the SBFDInitiator receives a valid S-BFD control packet in o If the SBFDInitiator receives a valid S-BFD control packet in
response to transmitted S-BFD control packet to a remote entity, response to transmitted S-BFD control packet to a remote entity,
then the SBFDInitiator SHOULD conclude that S-BFD control packet then the SBFDInitiator SHOULD conclude that S-BFD control packet
reached the intended remote entity. reached the 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 reachability 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
reachability and the action that would be triggered as a result reachability and the action that would be triggered as a result
skipping to change at page 15, line 47 skipping to change at page 14, line 13
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 control packet with Demand o If the SBFDInitiator receives an S-BFD control packet with Demand
(D) bit set, the packet MUST be discarded. (D) bit set, the packet MUST be discarded.
7.8. Additional SBFDReflector Behaviors 7.4. Diagnostic Values
o S-BFD control packets transmitted by the SBFDReflector MUST have Diagnostic value in both directions MAY be set to a certain value, to
"Required Min RX Interval" set to a value which expresses how many attempt to communicate further information to both ends.
incoming S-BFD control packets this SBFDReflector can handle. The Implementation MAY use already existing diagnostic values defined in
SBFDReflector can control how fast SBFInitiators will be sending Section 4.1 of [RFC5880]. However, details of such are outside the
S-BFD control packets to self by ensuring "Required Min RX scope of this specification.
Interval" indicates a value based on the current load.
o If the SBFDReflector wishes to communicate to some or all 7.5. The Poll Sequence
SBFDInitiators that monitored local entity is "temporarily out of
service", then S-BFD control packets with "state" set to ADMINDOWN
are sent to those SBFDInitiators. The SBFDInitiators, upon
reception of such packets, MUST NOT conclude loss of reachability
to corresponding remote entity, and MUST back off packet
transmission interval for the remote entity to an interval no
faster than 1 second. If the SBFDReflector is generating a
response S-BFD control packet for a local entity that is in
service, then "state" in response BFD control packets MUST be set
to UP.
o If an SBFDReflector receives an S-BFD control packet with Demand Poll sequence MAY be used in both directions. The Poll sequence MUST
(D) bit cleared, the packet MUST be discarded. operate in accordance with [RFC5880]. An SBFDReflector MAY use the
Poll sequence to slow down that rate at which S-BFD control packets
are generated from an SBFDInitiator. This is done by the
SBFDReflector using procedures described in Section 7.2.3 and setting
the Poll (P) bit in the reflected S-BFD control packet. The
SBFDInitiator is to then send the next S-BFD control packet with the
Final (F) bit set. If an SBFDReflector receives an S-BFD control
packet with Poll (P) bit set, then the SBFDReflector MUST respond
with an S-BFD control packet with Poll (P) bit cleared and Final (F)
bit set.
8. 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 continuity 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
skipping to change at page 17, line 20 skipping to change at page 15, line 33
behind this suggestion: behind this suggestion:
o S-BFD control packets can verify the reachability to intended o S-BFD control packets can verify the reachability to intended
target node, which allows one to have confidence that S-BFD echo target node, which allows one to have confidence that S-BFD echo
packets are u-turning on the expected target node. packets are u-turning on the expected target node.
o S-BFD control packets can detect when the target node is going out o S-BFD control packets can detect when the target node is going out
of service (i.e., via receiving back ADMINDOWN state). of service (i.e., via receiving back ADMINDOWN state).
The usage of the "Required Min Echo RX Interval" field is described The usage of the "Required Min Echo RX Interval" field is described
in Section 7.2.2 and Section 7.3.2. Because of the stateless nature in Section 7.3.2 and Section 7.2.2. Because of the stateless nature
of SBFDReflector sessions, a value specified the "Required Min Echo of SBFDReflector sessions, a value specified the "Required Min Echo
RX Interval" field in both directions is not very meaningful. Thus RX Interval" field is not very meaningful at SBFDReflector. Thus it
it is RECOMMENDED that the "Required Min Echo RX Interval" field is RECOMMENDED that the "Required Min Echo RX Interval" field simply
simply be set to zero in both directions. be set to zero from SBFDInitiator. SBFDReflector MAY set to
appropriate value to control the rate at which it wants to receives
SBFD echo packets.
Following aspects of S-BFD Echo functions are left as implementation Following aspects of S-BFD Echo functions are left as implementation
details, and are outside the scope of this document: details, and are outside the scope of this document:
o Format of the S-BFD echo packet (e.g., data beyond UDP header). o Format of the S-BFD echo packet (e.g., data beyond UDP header).
o Procedures on when and how to use the S-BFD Echo function. o Procedures on when and how to use the S-BFD Echo function.
11. Security Considerations 11. Security Considerations
Same security considerations as [RFC5880], [RFC5881], [RFC5883], Same security considerations as [RFC5880] apply to this document.
[RFC5884] and [RFC5885] apply to this document. Additionally, Additionally, implementing the following measures will strengthen
implementing the following measures will strengthen security aspects security aspects of the mechanism described by this document:
of the mechanism described by this document:
o SBFDInitiator MAY pick crypto sequence number based on o SBFDInitiator MAY pick a sequence number to be set in "sequence
authentication mode configured. Number" in authentication section based on 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 Auth Key ID in the incoming packet
[I-D.ietf-bfd-generic-crypto-auth] in the incoming packet and and verify the authentication data.
verify the authentication data.
o SBFDReflector MUST accept the packet if authentication is o SBFDReflector MUST accept the packet if authentication is
successful. successful.
o SBFDReflector MUST compute the Authentication data and MUST use o SBFDReflector MUST compute the Authentication data and MUST use
the same sequence number that it received in the S-BFD control the same sequence number that it received in the S-BFD control
packet that it is responding to. packet that it is responding to.
o SBFDInitiator MUST accept the S-BFD control packet if it either o SBFDInitiator SHOULD accept S-BFD control packet with sequence
comes with the same sequence number as it had sent or it's within number within permissible window. One potential approach is the
the window that it finds acceptable (described in detail in procedure explained in [I-D.ietf-bfd-generic-crypto-auth].
[I-D.ietf-bfd-generic-crypto-auth])
Using the above method, Using the above method,
o SBFDReflector continue to remain stateless despite using security. o SBFDReflector continue to remain stateless despite using security.
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 control packets irrespective of the sequence respond to S-BFD control packets irrespective of the sequence
number carried. number 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 control packets that come SBFDInitiator will only accept S-BFD control packets that come
with the sequence number that it had originally used when sending with the sequence number that it had originally used when sending
the S-BFD control packet. the S-BFD control packet.
Considerations about loop problems are covered in Appendix A.
12. IANA Considerations 12. IANA Considerations
No action is required by IANA for this document. No action is required by IANA for this document.
13. Acknowledgements 13. Acknowledgements
Authors would like to thank Jeffrey Haas, Greg Mirsky and Marc Authors would like to thank Jeffrey Haas, Greg Mirsky, Marc
Binderberger for performing thorough reviews and providing number of Binderberger, and Alvaro Retana for performing thorough reviews and
suggestions. Authors would like to thank Girija Raghavendra Rao, Les providing number of suggestions. Authors would like to thank Girija
Ginsberg, Srihari Raghavan, Vanitha Neelamegam and Vengada Prasad Raghavendra Rao, Les Ginsberg, Srihari Raghavan, Vanitha Neelamegam
Govindan from Cisco Systems for providing valuable comments. Authors and Vengada Prasad Govindan from Cisco Systems for providing valuable
would also like to thank John E. Drake and Pablo Frank for providing comments. Authors would also like to thank John E. Drake and Pablo
comments and suggestions. Frank for providing comments and suggestions.
14. 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
skipping to change at page 19, line 19 skipping to change at page 17, line 34
Sam Aldrin Sam Aldrin
Google Google
Email: aldrin.ietf@gmail.com Email: aldrin.ietf@gmail.com
15. References 15. References
15.1. Normative References 15.1. Normative References
[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,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[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, DOI 10.17487/RFC5880, June 2010,
<http://www.rfc-editor.org/info/rfc5880>.
[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.
15.2. 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.
[I-D.ietf-bfd-multipoint] [I-D.ietf-bfd-multipoint]
Katz, D., Ward, D., and J. Networks, "BFD for Multipoint Katz, D., Ward, D., and J. Networks, "BFD for Multipoint
Networks", draft-ietf-bfd-multipoint-06 (work in Networks", draft-ietf-bfd-multipoint-07 (work in
progress), May 2015. progress), August 2015.
[I-D.ietf-bfd-seamless-use-case] [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
Bhatia, M., Matsushima, S., Mirsky, G., and N. Kumar, DOI 10.17487/RFC0791, September 1981,
"Seamless Bidirectional Forwarding Detection (BFD) Use <http://www.rfc-editor.org/info/rfc791>.
Case", draft-ietf-bfd-seamless-use-case-02 (work in
progress), April 2015.
[RFC5885] Nadeau, T. and C. Pignataro, "Bidirectional Forwarding [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
Detection (BFD) for the Pseudowire Virtual Circuit (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
Connectivity Verification (VCCV)", RFC 5885, June 2010. December 1998, <http://www.rfc-editor.org/info/rfc2460>.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001,
<http://www.rfc-editor.org/info/rfc3031>.
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.
Node A (IP 192.0.2.1) ----------------- Node B (IP 192.0.2.2) Node A (IP 192.0.2.1) ----------------- Node B (IP 192.0.2.2)
| |
| |
Man in the Middle (MiM) Man in the Middle (MiM)
skipping to change at page 20, line 34 skipping to change at page 18, line 48
Suppose MiM sends a spoofed packet with MyDisc = 0x01010101, YourDisc Suppose MiM sends a spoofed packet with MyDisc = 0x01010101, YourDisc
= 0x02020202, source IP as 192.0.2.1 and dest IP as 192.0.2.2. When = 0x02020202, source IP as 192.0.2.1 and dest IP as 192.0.2.2. When
this packet reaches Node B, the reflector session on Node B will swap this packet reaches Node B, the reflector session on Node B will swap
the discriminators and IP addresses of the received packet and the discriminators and IP addresses of the received packet and
reflect it back, since YourDisc of the received packet matched with reflect it back, since YourDisc of the received packet matched with
reserved discriminator of Node B. The reflected packet that reached reserved discriminator of Node B. The reflected packet that reached
Node A will have MyDdisc=0x02020202 and YourDisc=0x01010101. Since Node A will have MyDdisc=0x02020202 and YourDisc=0x01010101. Since
YourDisc of the received packet matched the reserved discriminator of YourDisc of the received packet matched the reserved discriminator of
Node A, Node A will swap the discriminators and reflects the packet Node A, Node A will swap the discriminators and reflects the packet
back to Node B. Since reflectors MUST set the TTL of the reflected back to Node B. Since reflectors must set the TTL of the reflected
packets to 255, the above scenario will result in an infinite loop packets to 255, the above scenario will result in an infinite loop
with just one malicious packet injected from MiM. with just one malicious packet injected from MiM.
FYI: Packet fields do not carry any direction information, i.e., if FYI: Packet fields do not carry any direction information, i.e., if
this is Ping packet or reply packet. this is Ping packet or reply packet.
Solutions Solutions
The current proposals to avoid the loop problem are: The current proposals to avoid the loop problem are:
skipping to change at page 21, line 30 skipping to change at page 20, line 4
Carlos Pignataro Carlos Pignataro
Cisco Systems Cisco Systems
Email: cpignata@cisco.com Email: cpignata@cisco.com
Dave Ward Dave Ward
Cisco Systems Cisco Systems
Email: wardd@cisco.com Email: wardd@cisco.com
Manav Bhatia Manav Bhatia
Ionos Networks Ionos Networks
Email: manav@ionosnetworks.com Email: manav@ionosnetworks.com
Santosh Pallagatti Santosh Pallagatti
Juniper Networks
Email: santoshpk@juniper.net Email: santosh.pallagatti@gmail.com
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