draft-ietf-bfd-multihop-01.txt   draft-ietf-bfd-multihop-02.txt 
Network Working Group D. Katz Network Working Group D. Katz
Internet Draft Juniper Networks Internet Draft Juniper Networks
D. Ward D. Ward
Cisco Systems Cisco Systems
Expires: August, 2005 February, 2005 Expires: September, 2005 March, 2005
BFD for Multihop Paths BFD for Multihop Paths
draft-ietf-bfd-multihop-01.txt draft-ietf-bfd-multihop-02.txt
Status of this Memo Status of this Memo
By submitting this Internet-Draft, I certify that any applicable By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed, patent or other IPR claims of which I am aware have been disclosed,
or will be disclosed, and any of which I become aware will be or will be disclosed, and any of which I become aware will be
disclosed, in accordance with RFC 3668. disclosed, in accordance with RFC 3668.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
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material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/1id-abstracts.html http://www.ietf.org/1id-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html http://www.ietf.org/shadow.html
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved. Copyright (C) The Internet Society (2005). All Rights Reserved.
Abstract Abstract
This document describes the use of the Bidirectional Forwarding This document describes the use of the Bidirectional Forwarding
Detection protocol (BFD) over multihop paths, including Detection protocol (BFD) over multihop paths, including
unidirectional links. unidirectional links.
Conventions used in this document Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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BFD can also be useful on arbitrary paths between systems, which may BFD can also be useful on arbitrary paths between systems, which may
span multiple network hops and follow unpredictable paths. span multiple network hops and follow unpredictable paths.
Furthermore, a pair of systems may have multiple paths between them Furthermore, a pair of systems may have multiple paths between them
that may overlap. This document describes methods for using BFD in that may overlap. This document describes methods for using BFD in
such scenarios. such scenarios.
2. Issues 2. Issues
There are two primary issues in the use of BFD for multihop paths. There are two primary issues in the use of BFD for multihop paths.
The first is security and spoofing; the one-hop spec describes a The first is security and spoofing; [BFD-1HOP] describes a
lightweight method of avoiding spoofing by requiring a TTL/hop limit lightweight method of avoiding spoofing by requiring a TTL/hop limit
of 255 on both transmit and receive, but this obviously does not work of 255 on both transmit and receive, but this obviously does not work
across multiple hops. The utilization of BFD authentication across multiple hops. The utilization of BFD authentication
addresses this issue. addresses this issue.
The more subtle issue is that of demultiplexing multiple BFD sessions The more subtle issue is that of demultiplexing multiple BFD sessions
between the same pair of systems to the proper BFD session. In between the same pair of systems to the proper BFD session. In
particular, the first BFD packet received for a session may carry a particular, the first BFD packet received for a session may carry a
Your Discriminator value of zero, resulting in ambiguity as to which Your Discriminator value of zero, resulting in ambiguity as to which
session the packet should be associated. Once the discriminator session the packet should be associated. Once the discriminator
values have been exchanged, all further packets are demultiplexed to values have been exchanged, all further packets are demultiplexed to
the proper BFD session solely by the contents of the Your the proper BFD session solely by the contents of the Your
Discriminator field. Discriminator field.
The one-hop specification addresses this by requiring that multiple [BFD-1HOP] addresses this by requiring that multiple sessions
sessions traverse independent physical or logical links--the first traverse independent physical or logical links--the first packet is
packet is demultiplexed based on the link over which it was received. demultiplexed based on the link over which it was received. In the
In the more general case, this scheme cannot work, as two paths over more general case, this scheme cannot work, as two paths over which
which BFD is running may overlap to an arbitrary degree (including BFD is running may overlap to an arbitrary degree (including the
the first and/or last hop.) first and/or last hop.)
3. Demultiplexing Packets 3. Demultiplexing Packets
There are a number of possibilities for addressing the demultiplexing There are a number of possibilities for addressing the demultiplexing
issue which may be used, depending on the application. issue which may be used, depending on the application.
3.1. Totally Arbitrary Paths 3.1. Totally Arbitrary Paths
It may be desired to use BFD for liveness detection over paths for It may be desired to use BFD for liveness detection over paths for
which no part of the route is known (or if known, may not be stable.) which no part of the route is known (or if known, may not be stable.)
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4. Authentication 4. Authentication
By their nature, multihop paths expose BFD to spoofing. By their nature, multihop paths expose BFD to spoofing.
Implementations of BFD SHOULD utilize authentication over multihop Implementations of BFD SHOULD utilize authentication over multihop
paths to help mitigate denial-of-service attacks. paths to help mitigate denial-of-service attacks.
Normative References Normative References
[BFD] Katz, D., and Ward, D., "Bidirectional Forwarding Detection", [BFD] Katz, D., and Ward, D., "Bidirectional Forwarding Detection",
draft-ietf-bfd-base-01.txt, February, 2005. draft-ietf-bfd-base-02.txt, March, 2005.
[BFD-1HOP] Katz, D., and Ward, D., "BFD for IPv4 and IPv6 (Single [BFD-1HOP] Katz, D., and Ward, D., "BFD for IPv4 and IPv6 (Single
Hop)", draft-ietf-bfd-v4v6-1hop-01.txt, February, 2005. Hop)", draft-ietf-bfd-v4v6-1hop-02.txt, March, 2005.
[BFD-MPLS] Aggarwal, R., and Kompella, K., "BFD for MPLS LSPs", [BFD-MPLS] Aggarwal, R., and Kompella, K., "BFD for MPLS LSPs",
draft-ietf-bfd-mpls-01.txt, February, 2005. draft-ietf-bfd-mpls-01.txt, February, 2005.
[GTSM] Gill, V., et al, "The Generalized TTL Security Mechanism
(GTSM)", RFC 3682, February 2004.
[KEYWORD] Bradner, S., "Key words for use in RFCs to Indicate [KEYWORD] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997. Requirement Levels", RFC 2119, March 1997.
[OSPFv2] Moy, J., "OSPF Version 2", RFC 2328, April 1998. [OSPFv2] Moy, J., "OSPF Version 2", RFC 2328, April 1998.
[OSPFv3] Coltun, R., et al, "OSPF for IPv6", RFC 2740, December 1999. [OSPFv3] Coltun, R., et al, "OSPF for IPv6", RFC 2740, December 1999.
Security Considerations Security Considerations
No additional security issues are raised in this document beyond No additional security issues are raised in this document beyond
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Dave Ward Dave Ward
Cisco Systems Cisco Systems
170 W. Tasman Dr. 170 W. Tasman Dr.
San Jose, CA 95134 USA San Jose, CA 95134 USA
Phone: +1-408-526-4000 Phone: +1-408-526-4000
Email: dward@cisco.com Email: dward@cisco.com
Changes from the previous draft Changes from the previous draft
No changes were made other than updating references and boilerplate No changes were made other than updating references.
language.
Full Copyright Notice Full Copyright Notice
Copyright (C) The Internet Society (2004). This document is subject Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights. except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement Acknowledgement
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
This document expires in August, 2005. This document expires in September, 2005.
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