draft-ietf-bfd-v4v6-1hop-00.txt   draft-ietf-bfd-v4v6-1hop-01.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: January, 2005 July, 2004 Expires: August, 2005 February, 2005
BFD for IPv4 and IPv6 (Single Hop) BFD for IPv4 and IPv6 (Single Hop)
draft-ietf-bfd-v4v6-1hop-00.txt draft-ietf-bfd-v4v6-1hop-01.txt
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with By submitting this Internet-Draft, I certify that any applicable
all provisions of Section 10 of RFC2026. 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
disclosed, in accordance with RFC 3668.
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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 over IPv4 and IPv6 for single IP hops. It further Detection protocol over IPv4 and IPv6 for single IP hops. It further
describes the use of BFD with OSPFv2, OSPFv3, and IS-IS. Comments on describes the use of BFD with OSPFv2, OSPFv3, and IS-IS. Comments on
this draft should be directed to rtg-bfd@ietf.org. this draft should be directed to rtg-bfd@ietf.org.
Conventions used in this document Conventions used in this document
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BFD Echo packets MUST be transmitted in UDP packets with destination BFD Echo packets MUST be transmitted in UDP packets with destination
UDP port 3785 in an IPv6 packet. The setting of the UDP source port UDP port 3785 in an IPv6 packet. The setting of the UDP source port
is outside the scope of this specification. The source and is outside the scope of this specification. The source and
destination addresses MUST both be associated with the local system. destination addresses MUST both be associated with the local system.
The destination address MUST be chosen in such a way as to cause the The destination address MUST be chosen in such a way as to cause the
remote system to forward the packet back to the local system. remote system to forward the packet back to the local system.
5. TTL/Hop Count Issues 5. TTL/Hop Count Issues
All BFD Control packets for sessions operating according to this If BFD authentication is not in use, all BFD Control packets for
specification MUST be sent with a TTL or Hop Count value of 255. All sessions operating according to this specification MUST be sent with
received BFD Control packets that are demultiplexed to sessions a TTL or Hop Count value of 255. All received BFD Control packets
operating according to this specification MUST be discarded if the that are demultiplexed to sessions operating according to this
received TTL or Hop Count is not equal to 255. A discussion of this specification MUST be discarded if the received TTL or Hop Count is
mechanism can be found in [GTSM]. not equal to 255. A discussion of this mechanism can be found in
[GTSM].
If BFD authentication is in use, any value of TTL/Hop Count MAY be
used in transmitted packets, and received packets MUST NOT be
discarded based on the received TTL/Hop Count.
6. Addressing Issues 6. Addressing Issues
On a subnetted network, BFD Control packets MUST be transmitted with On a subnetted network, BFD Control packets MUST be transmitted with
source and destination addresses that are part of the subnet source and destination addresses that are part of the subnet
(addressed from and to interfaces on the subnet.) (addressed from and to interfaces on the subnet.)
On an addressed but unsubnetted point-to-point link, BFD Control On an addressed but unsubnetted point-to-point link, BFD Control
packets MUST be transmitted with source and destination addresses packets MUST be transmitted with source and destination addresses
that match the addresses configured on that link. that match the addresses configured on that link.
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The two versions of OSPF, as well as IS-IS, all suffer from an The two versions of OSPF, as well as IS-IS, all suffer from an
architectural limitation, namely that their Hello protocols are architectural limitation, namely that their Hello protocols are
limited in the granularity of failure their detection times. In limited in the granularity of failure their detection times. In
particular, OSPF has a minimum detection time of two seconds, and IS- particular, OSPF has a minimum detection time of two seconds, and IS-
IS has a minimum detection time of one second. IS has a minimum detection time of one second.
BFD MAY be used to achieve arbitrarily small detection times for BFD MAY be used to achieve arbitrarily small detection times for
these protocols by supplanting the Hello protocols used in each case. these protocols by supplanting the Hello protocols used in each case.
It should be noted that the purpose of using BFD in this context is
not to replace the adjacency timeout mechanism, nor is it to
demonstrate that the network is fully functional for the use of the
routing protocol, but is simply to advise the routing protocol that
there are problems forwarding the data protocol for which the routing
protocol is calculating routes.
7.1. Session Establishment 7.1. Session Establishment
The mechanism by which a BFD session is established in this The mechanism by which a BFD session is established in this
environment is outside the scope of this specification. An obvious environment is outside the scope of this specification. An obvious
choice would be to use the discovery mechanism inherent in the Hello choice would be to use the discovery mechanism inherent in the Hello
protocols in OSPF and IS-IS to bootstrap the establishment of a BFD protocols in OSPF and IS-IS to bootstrap the establishment of a BFD
session. session.
Any BFD sessions established to support OSPF and IS-IS across a Any BFD sessions established to support OSPF and IS-IS across a
single IP hop MUST operate in accordance with the rest of this single IP hop MUST operate in accordance with the rest of this
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or if multiple protocols are being advertised but the protocols must or if multiple protocols are being advertised but the protocols must
share a common topology, a Hello protocol timeout SHOULD be emulated share a common topology, a Hello protocol timeout SHOULD be emulated
for the associated OSPF neighbors and/or IS-IS adjacencies. for the associated OSPF neighbors and/or IS-IS adjacencies.
If multiple data protocols are advertised in the routing protocol If multiple data protocols are advertised in the routing protocol
Hello, and the routing protocol supports different topologies for Hello, and the routing protocol supports different topologies for
each data protocol, the failing data protocol SHOULD no longer be each data protocol, the failing data protocol SHOULD no longer be
advertised in Hello packets in order to signal a lack of connectivity advertised in Hello packets in order to signal a lack of connectivity
for that protocol. for that protocol.
If a BFD session never reaches Up state (possibly because the remote Note that it is possible in some failure scenarios for the network to
system does not support BFD), this MUST NOT preclude the be in a state such that the IGP comes up, but the BFD session cannot
establishment of an OSPF neighbor or an IS-IS adjacency. be established, and, more particularly, data cannot be forwarded. To
avoid this situation, it would be beneficial to not allow the IGP to
establish a neighbor/adjacency. However, this would preclude the
operation of the IGP in an environment in which not all systems
support BFD.
Therefore, if a BFD session is not in Up state (possibly because the
remote system does not support BFD), it is OPTIONAL to preclude the
establishment of an OSPF neighbor or an IS-IS adjacency. The choice
of whether to do so SHOULD be controlled by means outside the scope
of this specification, such as configuration or other mechanisms.
7.4. Interactions with OSPF and IS-IS with Graceful Restart 7.4. Interactions with OSPF and IS-IS with Graceful Restart
The Graceful Restart functions in OSPF [OSPF-GRACE] and IS-IS [ISIS- The Graceful Restart functions in OSPF [OSPF-GRACE] and IS-IS [ISIS-
GRACE] are predicated on the existence of a separate forwarding plane GRACE] are predicated on the existence of a separate forwarding plane
that does not necessarily share fate with the control plane in which that does not necessarily share fate with the control plane in which
the routing protocols operate. In particular, the assumption is that the routing protocols operate. In particular, the assumption is that
the forwarding plane can continue to function while the protocols the forwarding plane can continue to function while the protocols
restart and sort things out. restart and sort things out.
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BFD is independent of the control plane on the local system, and the BFD is independent of the control plane on the local system, and the
remote system has been transmitting BFD Control packets with the C remote system has been transmitting BFD Control packets with the C
bit set, the graceful restart SHOULD be aborted and the topology bit set, the graceful restart SHOULD be aborted and the topology
change made visible to the network as outlined in section 7.3. change made visible to the network as outlined in section 7.3.
If BFD shares its fate with the control plane on either system If BFD shares its fate with the control plane on either system
(either the local system shares fate with the control plane, or the (either the local system shares fate with the control plane, or the
remote system is transmitting BFD packets with the C bit set to remote system is transmitting BFD packets with the C bit set to
zero), it is not useful during graceful restart, as the BFD session zero), it is not useful during graceful restart, as the BFD session
is likely to fail regardless of the state of the forwarding plane. is likely to fail regardless of the state of the forwarding plane.
In this situation, if a BFD session fails while graceful restart is The action to take in this case depends on the capabilities of the
taking place (or if the BFD session failure triggers a graceful IGP.
restart event), the graceful restart SHOULD be allowed to complete
and the topology change should not be made visible to the network as 7.4.1. OSPF Graceful Restart With Control Plane Fate Sharing
outlined in section 7.3.
OSPF has a "planned" restart mechanism, in which the restarting
system notifies its neighbors that it is about to perform a restart.
In this situation, if a BFD session fails while the neighbor is
performing a graceful restart, the graceful restart SHOULD be allowed
to complete and the topology change should not be made visible to the
network as outlined in section 7.3.
For unplanned restarts (in which the neighbor has not notified the
local system of its intention to restart), the OSPF Graceful Restart
specification allows a Graceful Restart to take place if the system
restarts prior to the expiration of the OSPF neighbor relationship.
In this case, the BFD Detection Time is likely to expire prior to the
restart, and the neighbor relationship SHOULD be torn down. In the
unlikely event that the system restarts quickly enough, and the
system chooses to attempt a Graceful Restart, the graceful restart
SHOULD be allowed to complete and the topology change should not be
made visible to the network as outlined in section 7.3.
7.4.2. ISIS Graceful Restart With Control Plane Fate Sharing
ISIS Graceful Restart does not signal a "planned" restart; its
mechanism does not begin until after the system has restarted. If
the BFD session expires prior to the restart of the system, there is
no way for the neighbors to know that a Graceful Restart will take
place.
If a planned restart is about to place, the restarting system MAY
change the BFD timing parameters on a temporary basis in such a way
as to make the Detection Time greater than or equal to the ISIS
adjacency timeout. This will provide the restarting system the same
opportunity to enter Graceful Restart as it would have without BFD.
In this case, the restarted system SHOULD avoid sending any BFD
Control packets until there is a high likelihood that its neighbors
know it is performing a Graceful Restart, since the neighbors will
tear down their BFD sessions when those sessions restart.
In any case, if a BFD session fails while the neighbor is known to be
performing a Graceful Restart, the Graceful Restart SHOULD be allowed
to complete and the topology change should not be made visible to the
network as outlined in section 7.3.
If the BFD session fails, and it is not known whether the neighbor is
performing a Graceful Restart, the BFD session failure SHOULD be made
visible to the network as outlined in section 7.3.
7.5. OSPF Virtual Links 7.5. OSPF Virtual Links
If it is desired to use BFD for failure detction of OSPF Virtual If it is desired to use BFD for failure detction of OSPF Virtual
Links, the mechanism described in [BFD-MULTI] MUST be used, since Links, the mechanism described in [BFD-MULTI] MUST be used, since
OSPF Virtual Links may traverse an arbitrary number of hops. BFD OSPF Virtual Links may traverse an arbitrary number of hops. BFD
Authentication SHOULD be used and is strongly encouraged. Authentication SHOULD be used and is strongly encouraged.
8. BFD for use with Tunnels 8. BFD for use with Tunnels
A number of mechanisms are available to tunnel IPv4 and IPv6 over A number of mechanisms are available to tunnel IPv4 and IPv6 over
arbitrary topologies. If the tunnel mechanism does not decrement the arbitrary topologies. If the tunnel mechanism does not decrement the
TTL or hop count of the network protocol carried within, the TTL or hop count of the network protocol carried within, the
mechanism described in this document may be used to provide liveness mechanism described in this document may be used to provide liveness
detection for the tunnel. The BFD Authentication mechanism SHOULD be detection for the tunnel. The BFD Authentication mechanism SHOULD be
used and is strongly encouraged. used and is strongly encouraged.
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-00.txt, July, 2004. draft-ietf-bfd-base-01.txt, February, 2005.
[BFD-MULTI] Katz, D., and Ward, D., "BFD for Multihop Paths", draft- [BFD-MULTI] Katz, D., and Ward, D., "BFD for Multihop Paths", draft-
ietf-bfd-multihop-00.txt, July, 2004. ietf-bfd-multihop-01.txt, February, 2005.
[GTSM] Gill, V., et al, "The Generalized TTL Security Mechanism [GTSM] Gill, V., et al, "The Generalized TTL Security Mechanism
(GTSM)", RFC 3682, February 2004. (GTSM)", RFC 3682, February 2004.
[ISIS] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and dual [ISIS] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and dual
environments", RFC 1195, December 1990. environments", RFC 1195, December 1990.
[ISIS-GRACE] Shand, M., and Ginsberg, L., "Restart signaling for IS- [ISIS-GRACE] Shand, M., and Ginsberg, L., "Restart signaling for IS-
IS", draft-ietf-isis-restart-05.txt, January 2004. IS", RFC 3847, July 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.
[OSPF-GRACE] Moy, J., et al, "Graceful OSPF Restart", RFC 3623, [OSPF-GRACE] Moy, J., et al, "Graceful OSPF Restart", RFC 3623,
November 2003. November 2003.
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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
The only significant changes to this version are the addition of The only significant changes to this version are the option of not
language describing tunnels and OSPF virtual links. All other using the TTL=255 hack when authentication is in use, the option of
changes are editorial in nature. suppressing ISIS and OSPF neighbors while the BFD session is down,
and further explication of the interactions with Graceful Restart.
All other changes are editorial in nature.
Full Copyright Notice Full Copyright Notice
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Acknowledgement Acknowledgement
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This document expires in August, 2005.
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