< draft-katz-ward-bfd-v4v6-1hop-00.txt   draft-katz-ward-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
Category: Informational August, 2003 Category: Informational May, 2004
Expires: February, 2004 Expires: November, 2004
BFD for IPv4 and IPv6 (Single Hop) BFD for IPv4 and IPv6 (Single Hop)
draft-katz-ward-bfd-v4v6-1hop-00.txt draft-katz-ward-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 This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
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
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
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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/ietf/1id-abstracts.txt http://www.ietf.org/ietf/1id-abstracts.txt
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http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved. Copyright (C) The Internet Society (2004). 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 IPv4 and IPv6 for single IP hops. It Detection protocol over IPv4 and IPv6 for single IP hops. It further
further describes the use of BFD with OSPFv2 [OSPFv2], OSPFv3 describes the use of BFD with OSPFv2, OSPFv3, and IS-IS. Comments on
[OSPFv3], and ISIS [ISIS]. this draft should be directed to rtg-bfd@ietf.org.
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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [KEYWORDS]. document are to be interpreted as described in RFC-2119 [KEYWORDS].
1. Introduction 1. Introduction
One very desirable application for BFD is to track IPv4 and IPv6 One very desirable application for BFD [BFD] is to track IPv4 and
connectivity between directly-connected systems. This could be used IPv6 connectivity between directly-connected systems. This could be
to supplant the detection mechanisms in ISIS and OSPF, or to monitor used to supplant the detection mechanisms in IS-IS and OSPF, or to
router-host connectivity, among other applications. monitor router-host connectivity, among other applications.
This document describes the particulars necessary to use BFD in this This document describes the particulars necessary to use BFD in this
environment, and describes how BFD can be used in conjunction OSPFv2, environment, and describes how BFD can be used in conjunction OSPFv2
OSPFv3, and ISIS. [OSPFv2], OSPFv3 [OSPFv3], and IS-IS [ISIS].
2. Applications and Limitations 2. Applications and Limitations
This application of BFD can be used by any pair of systems This application of BFD can be used by any pair of systems
communicating via IPv4 and/or IPv6 across a single IP hop that can be communicating via IPv4 and/or IPv6 across a single IP hop that can be
associated with an incoming interface. This includes, but is not associated with an incoming interface. This includes, but is not
limited to, physical media, virtual circuits, and tunnels. limited to, physical media, virtual circuits, and tunnels.
Each BFD session between a pair of systems must traverse a separate Each BFD session between a pair of systems MUST traverse a separate
path in both directions. path in both directions.
If BFD is to be used in conjunction with both IPv4 and IPv6 on a
particular link, a separate BFD session MUST be established for each
protocol (and thus encapsulated by that protocol) over that link.
3. Initialization and Demultiplexing 3. Initialization and Demultiplexing
In this application, there will be only a single BFD session between In this application, there will be only a single BFD session between
two systems over a given interface (logical or physical.) The BFD two systems over a given interface (logical or physical) for a
session must be bound to this interface. As such, both sides of a particular protocol. The BFD session must be bound to this
session MUST use "Active" mode (sending BFD Control packets with a interface. As such, both sides of a session MUST take the "Active"
zero value of Your Discriminator) and any BFD packet from the remote role (sending initial BFD Control packets with a zero value of Your
machine with a zero value of Your Discriminator MUST be associated Discriminator) and any BFD packet from the remote machine with a zero
with the session bound to the remote system and interface. value of Your Discriminator MUST be associated with the session bound
to the remote system, interface, and protocol.
4. Encapsulation 4. Encapsulation
4.1. BFD for IPv4 4.1. BFD for IPv4
In the case of IPv4, BFD Control packets MUST be transmitted in UDP In the case of IPv4, BFD Control packets MUST be transmitted in UDP
packets with destination port 3784, within an IPv4 packet. The packets with destination port 3784, within an IPv4 packet. The
source port MUST be in the range 49152 through 65535. The same UDP source port MUST be in the range 49152 through 65535. The same UDP
source port number MUST be used for all BFD Control packets source port number MUST be used for all BFD Control packets
associated with a particular session. The source port number SHOULD associated with a particular session. The source port number SHOULD
be unique among all BFD sessions on the system. If more than 16384 be unique among all BFD sessions on the system. If more than 16384
BFD sessions are simultaneously active, UDP source port numbers MAY BFD sessions are simultaneously active, UDP source port numbers MAY
be reused on multiple sessions, but the number of distinct uses of be reused on multiple sessions, but the number of distinct uses of
the same UDP source port number SHOULD be minimized. An the same UDP source port number SHOULD be minimized. An
implementation MAY use the UDP port source number to aid in implementation MAY use the UDP port source number to aid in
demultiplexing incoming BFD Control packets, but ultimately the demultiplexing incoming BFD Control packets, but ultimately the
mechanisms in [BFD] MUST be used to demultiplex incoming packets to mechanisms in [BFD] MUST be used to demultiplex incoming packets to
the proper session. the proper session.
BFD Echo packets are transmitted in UDP packets with destination UDP BFD Echo packets MUST be transmitted in UDP packets with destination
port 3785 in an IPv4 packet. The setting of the UDP source port is UDP port 3785 in an IPv4 packet. The setting of the UDP source port
outside the scope of this specification. The destination address is outside the scope of this specification. The destination address
MUST be chosen in such a way as to cause the remote system to forward MUST be chosen in such a way as to cause the remote system to forward
the packet back to the local system. The source address MUST be the packet back to the local system. The source address MUST be
chosen in such a way as to preclude the remote system from generating chosen in such a way as to preclude the remote system from generating
ICMP Redirect messages (in particular, the source address MUST NOT be ICMP Redirect messages (in particular, the source address MUST NOT be
part of the subnet bound to the interface over which the BFD Echo part of the subnet bound to the interface over which the BFD Echo
packet is being transmitted.) packet is being transmitted.)
4.2. BFD for IPv6 4.2. BFD for IPv6
In the case of IPv6, BFD Control packets MUST be transmitted in UDP In the case of IPv6, BFD Control packets MUST be transmitted in UDP
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associated with a particular session. The source port number SHOULD associated with a particular session. The source port number SHOULD
be unique among all BFD sessions on the system. If more than 16384 be unique among all BFD sessions on the system. If more than 16384
BFD sessions are simultaneously active, UDP source port numbers MAY BFD sessions are simultaneously active, UDP source port numbers MAY
be reused on multiple sessions, but the number of distinct uses of be reused on multiple sessions, but the number of distinct uses of
the same UDP source port number SHOULD be minimized. An the same UDP source port number SHOULD be minimized. An
implementation MAY use the UDP port source number to aid in implementation MAY use the UDP port source number to aid in
demultiplexing incoming BFD Control packets, but ultimately the demultiplexing incoming BFD Control packets, but ultimately the
mechanisms in [BFD] MUST be used to demultiplex incoming packets to mechanisms in [BFD] MUST be used to demultiplex incoming packets to
the proper session. the proper session.
BFD Echo packets are transmitted in UDP packets with destination UDP BFD Echo packets MUST be transmitted in UDP packets with destination
port 3785 in an IPv6 packet. The setting of the UDP source port is UDP port 3785 in an IPv6 packet. The setting of the UDP source port
outside the scope of this specification. The source and destination is outside the scope of this specification. The source and
addresses MUST both be associated with the local system. The destination addresses MUST both be associated with the local system.
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 Issues 5. TTL/Hop Count Issues
All BFD packets for sessions operating in this mode MUST be sent with All BFD Control packets for sessions operating according to this
a TTL value of 255. All received BFD packets that are demultiplexed specification MUST be sent with a TTL or Hop Count value of 255. All
to sessions operating in this mode MUST be discarded if the received received BFD Control packets that are demultiplexed to sessions
TTL is not equal to 255. operating according to this specification MUST be discarded if the
received TTL or Hop Count is not equal to 255.
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.
On an unnumbered point-to-point link, the source address of a BFD On an unnumbered point-to-point link, the source address of a BFD
Control packet MUST NOT be used to identify the session. This means Control packet MUST NOT be used to identify the session. This means
that the initial BFD packet MUST be accepted with any source address, that the initial BFD packet MUST be accepted with any source address,
and that subsequent BFD packets MUST be demultiplexed solely by the and that subsequent BFD packets MUST be demultiplexed solely by the
My Discriminator field (as is always the case.) This allows the My Discriminator field (as is always the case.) This allows the
source address to change if necessary. source address to change if necessary. Note that the TTL/Hop Count
check described in section 5 precludes the BFD packets from having
come from any source other than the immediate neighbor.
7. BFD for use with OSPFv2, OSPFv3, and ISIS 7. BFD for use with OSPFv2, OSPFv3, and IS-IS
The two versions of OSPF, as well as ISIS, 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 particular, OSPF has a minimum detection time of two seconds, and IS-
ISIS 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.
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 ISIS 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 ISIS MUST operate in Any BFD sessions established to support OSPF and IS-IS across a
accordance with the rest of this document. single IP hop MUST operate in accordance with the rest of this
document.
If multiple protocols wish to establish BFD sessions with the same If multiple routing protocols wish to establish BFD sessions with the
remote system, all MUST share a single BFD session. same remote system for the same data protocol, all MUST share a
single BFD session.
7.2. Session Parameters 7.2. Session Parameters
The setting of the various timing parameters and modes in this The setting of the various timing parameters and modes in this
application are outside the scope of this specification. application are outside the scope of this specification.
Note that all protocols sharing a session will operate using the same Note that all protocols sharing a session will operate using the same
parameters. The mechanism for choosing the parameters among those parameters. The mechanism for choosing the parameters among those
desired by the various protocols are outside the scope of this desired by the various protocols are outside the scope of this
specification. specification.
7.3. Interactions with OSPF and ISIS 7.3. Interactions with OSPF and IS-IS without Graceful Restart
When a BFD session transitions from Up to Failing, a Hello protocol When a BFD session transitions from Up to Failing, action SHOULD be
timeout SHOULD be emulated for the associated OSPF neighbors and/or taken in the routing protocol to signal the lack of connectivity for
ISIS adjacencies. the data protocol (IPv4 or IPv6) over which BFD is running. If only
one data protocol is being advertised in the routing protocol Hello,
or if multiple protocols are being advertised but the protocols must
share a common topology, a Hello protocol timeout SHOULD be emulated
for the associated OSPF neighbors and/or IS-IS adjacencies.
An OSPF neighbor or an ISIS adjacency MUST be allowed to come up, If multiple data protocols are advertised in the routing protocol
according to the appropriate specification, regardless of the state Hello, and the routing protocol supports different topologies for
of the associated BFD session. each data protocol, the failing data protocol SHOULD no longer be
advertised in Hello packets in order to signal a lack of connectivity
for that protocol.
7.4. OSPF Virtual Links If a BFD session never comes up (possibly because the remote system
does not support BFD), this MUST NOT preclude the establishment of an
OSPF neighbor or an IS-IS adjacency.
7.4. Interactions with OSPF and IS-IS with Graceful Restart
The Graceful Restart functions in OSPF [OSPF-GRACE] and IS-IS [ISIS-
GRACE] are predicated on the existence of a separate forwarding plane
that does not necessarily share fate with the control plane in which
the routing protocols operate. In particular, the assumption is that
the forwarding plane can continue to function while the protocols
restart and sort things out.
BFD implementations announce via the Control Plane Independent (C)
bit whether or not BFD shares fate with the control plane. This
information is used to determine the actions to be taken in
conjunction with Graceful Restart.
If BFD does not share its fate with the control plane on either
system, it can be used to determine whether Graceful Restart is NOT
viable (the forwarding plane is not operating.) In this situation,
if a BFD session fails while graceful restart is taking place, and
BFD is independent of the control plane on the local system, and the
remote system has been transmitting BFD Control packets with the C
bit set, the graceful restart SHOULD be aborted and the topology
change made visible to the network as outlined in section 7.3.
If BFD shares its fate with the control plane on either system
(either the local system shares fate with the control plane, or the
remote system is transmitting BFD packets with the C bit set to
zero), it is not useful during graceful restart, as the BFD session
is likely to fail regardless of the state of the forwarding plane.
In this situation, if a BFD session fails while graceful restart is
taking place (or if the BFD session failure triggers a graceful
restart event), 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.
7.5. OSPF Virtual Links
The use of BFD to support failure detection of OSPF Virtual Links is The use of BFD to support failure detection of OSPF Virtual Links is
for further study and is not yet supported, pending the full for further study and is not yet supported, pending the full
specification of multihop BFD. specification of multihop BFD.
Authors' Addresses Authors' Addresses
Dave Katz Dave Katz
Juniper Networks Juniper Networks
1194 N. Mathilda Ave. 1194 N. Mathilda Ave.
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Phone: +1-408-745-2000 Phone: +1-408-745-2000
Email: dkatz@juniper.net Email: dkatz@juniper.net
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
The changes in this draft from the previous version are primarily
editorial. Some language has been clarified, a description of how to
handle multiprotocol routing has been added, and a section on the
interaction with graceful restart has also been added. The two
versions of this draft are believed to be fully interoperable.
Normative References Normative References
[BFD] Katz, D., and Ward, D., "Bidirectional Forwarding Detection", [BFD] Katz, D., and Ward, D., "Bidirectional Forwarding Detection",
draft-katz-ward-bfd-01.txt, August 2003. draft-katz-ward-bfd-02.txt, May, 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-
IS", draft-ietf-isis-restart-05.txt, January 2004.
[KEYWORD] Bradner, S., "Key words for use in RFCs to Indicate
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,
November 2003.
Security Considerations Security Considerations
In this application, the use of TTL=255 on transmit and receive is In this application, the use of TTL=255 on transmit and receive is
viewed as supplying equivalent security characteristics to other viewed as supplying equivalent security characteristics to other
protocols used in the infrastructure, as it is not trivially protocols used in the infrastructure, as it is not trivially
spoofable. Other security mechanisms are for further study. spoofable. Other security mechanisms are for further study.
Full Copyright Notice Full Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved. Copyright (C) The Internet Society (2004). All Rights Reserved.
This document and translations of it may be copied and furnished to This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of Internet organizations, except as needed for the purpose of
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