Bidirectional Forwarding Detection (BFD) for IPv4 and IPv6 (Single Hop)
The information below is for an old version of the document that is already published as an RFC.
This is an older version of an Internet-Draft that was ultimately published as RFC 5881.
|Dave Katz , David Ward
|2020-01-21 (Latest revision 2010-01-05)
|Internet Engineering Task Force (IETF)
|Intended RFC status
|Mailing list discussion
|Became RFC 5881 (Proposed Standard)
|Send notices to
Network Working Group D. Katz Internet Draft Juniper Networks Intended status: Proposed Standard D. Ward Juniper Networks Expires: July, 2010 January 5, 2010 BFD for IPv4 and IPv6 (Single Hop) draft-ietf-bfd-v4v6-1hop-11.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the BSD License. Katz, Ward [Page 1] Internet Draft BFD for IPv4 and IPv6 (Single Hop) January, 2010 Abstract This document describes the use of the Bidirectional Forwarding Detection protocol over IPv4 and IPv6 for single IP hops. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119 [KEYWORDS]. 1. Introduction One very desirable application for BFD [BFD] is to track IPv4 and IPv6 connectivity between directly-connected systems. This could be used to supplement the detection mechanisms in routing protocols, or to monitor router-host connectivity, among other applications. This document describes the particulars necessary to use BFD in this environment. Interactions between BFD and other protocols and system functions are described in the BFD Generic Applications document [BFD-GENERIC]. 2. Applications and Limitations This application of BFD can be used by any pair of systems communicating via IPv4 and/or IPv6 across a single IP hop that is associated with an incoming interface. This includes, but is not limited to, physical media, virtual circuits, and tunnels. Each BFD session between a pair of systems MUST traverse a separate network-layer path in both directions. This is necessary for demultiplexing to work properly, and also because (by definition) multiple sessions would otherwise be protecting the same path. If BFD is to be used in conjunction with both IPv4 and IPv6 on a particular path, a separate BFD session MUST be established for each protocol (and thus encapsulated by that protocol) over that link. If the BFD Echo function is used, transmitted packets are immediately routed back towards the sender on the interface over which they were sent. This may interact with other mechanisms that are used on the Katz, Ward [Page 2] Internet Draft BFD for IPv4 and IPv6 (Single Hop) January, 2010 two systems that employ BFD. In particular, ingress filtering [BCP38] is incompatible with the way Echo packets need to be sent. Implementations that support the Echo function MUST either ensure that ingress filtering is not used on an interface that employs the Echo function, or need make an exception for ingress filtering Echo packets. An implementation of the Echo function also requires Application Programming Interfaces (APIs) that may not exist on all systems. A system implementing the Echo function MUST be capable of sending packets to its own address, which will typically require bypassing the normal forwarding lookup. This typically requires access to APIs that bypass IP layer functionality. Please note that BFD is intended as a connectivity check/connection verification OAM mechanism. It is applicable for network-based services (e.g. router-to-router, subscriber-to-gateway, LSP/circuit endpoints and service appliance failure detection). In these scenarios it is required that the operator correctly provision the rates at which BFD is transmitted to avoid congestion (e.g link, I/O, CPU) and false failure detection. It is not applicable for application-to-application failure detection across the Internet because it does not have sufficient capability to do necessary congestion detection and avoidance and therefore cannot prevent congestion collapse. Host-to-host or application-to-application deployment across the Internet will require the encapsulation of BFD within a transport that provides "TCP-friendly" [TFRC] behavior. 3. Initialization and Demultiplexing In this application, there will be only a single BFD session between two systems over a given interface (logical or physical) for a particular protocol. The BFD session must be bound to this interface. As such, both sides of a session MUST take the "Active" role (sending initial BFD Control packets with a zero value of Your Discriminator) and any BFD packet from the remote machine with a zero value of Your Discriminator MUST be associated with the session bound to the remote system, interface, and protocol. Katz, Ward [Page 3] Internet Draft BFD for IPv4 and IPv6 (Single Hop) January, 2010 4. Encapsulation BFD Control packets MUST be transmitted in UDP packets with destination port 3784, within an IPv4 or IPv6 packet. The source port MUST be in the range 49152 through 65535. The same UDP source port number MUST be used for all BFD Control packets associated with a particular session. The source port number SHOULD be unique among all BFD sessions on the system. If more than 16384 BFD sessions are simultaneously active, UDP source port numbers MAY be reused on multiple sessions, but the number of distinct uses of the same UDP source port number SHOULD be minimized. An implementation MAY use the UDP port source number to aid in demultiplexing incoming BFD Control packets, but ultimately the mechanisms in [BFD] MUST be used to demultiplex incoming packets to the proper session. BFD Echo packets MUST be transmitted in UDP packets with destination UDP port 3785 in an IPv4 or IPv6 packet. The setting of the UDP source port 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 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 ICMP or Neighbor Discovery Redirect messages. In particular, the source address SHOULD NOT be part of the subnet bound to the interface over which the BFD Echo packet is being transmitted, and it SHOULD NOT be an IPv6 link-local address, unless it is known by other means that the remote system will not send Redirects. BFD Echo packets MUST be transmitted in such a way as to ensure that they are received by the remote system. On multiaccess media, for example, this requires that the destination datalink address corresponds to the remote system. The above requirements may require the bypassing of some common IP layer functionality, particularly in host implementations. Katz, Ward [Page 4] Internet Draft BFD for IPv4 and IPv6 (Single Hop) January, 2010 5. TTL/Hop Limit Issues If BFD authentication is not in use on a session, all BFD Control packets for the session MUST be sent with a TTL or Hop Limit value of 255. All received BFD Control packets that are demultiplexed to the session MUST be discarded if the received TTL or Hop Limit is not equal to 255. A discussion of this mechanism can be found in [GTSM]. If BFD authentication is in use on a session, all BFD Control packets MUST be sent with a TTL or Hop Limit value of 255. All received BFD Control packets that are demultiplexed the session MAY be discarded if the received TTL or Hop Limit is not equal to 255. If the TTL/Hop Limit check is made, it MAY be done before any cryptographic authentication takes place if this will avoid unnecessary calculation that would be detrimental to the receiving system. In the context of this section, "authentication in use" means that the system is sending BFD control packets with the Authentication bit set and with the Authentication Section included, and that all unauthenticated packets demultiplexed to the session are discarded, per the BFD base specification. 6. Addressing Issues Implementations MUST ensure that all BFD Control packets are transmitted over the one-hop path being protected by BFD. On a multiaccess network, BFD Control packets MUST be transmitted with source and destination addresses that are part of the subnet (addressed from and to interfaces on the subnet.) On a point-to-point link, the source address of a BFD Control packet MUST NOT be used to identify the session. This means that the initial BFD packet MUST be accepted with any source address, and that subsequent BFD packets MUST be demultiplexed solely by the Your Discriminator field (as is always the case.) This allows the source address to change if necessary. If the received source address changes, the local system MUST NOT use that address as the destination in outgoing BFD Control packets; rather it MUST continue to use the address configured at session creation. An implementation MAY notify the application that the neighbor's source address has changed, so that the application might choose to change the destination address or take some other action. Note that the TTL/Hop Limit check described in section 5 (or the use of authentication) precludes the BFD packets from having come from any source other than the immediate neighbor. Katz, Ward [Page 5] Internet Draft BFD for IPv4 and IPv6 (Single Hop) January, 2010 7. BFD for use with Tunnels A number of mechanisms are available to tunnel IPv4 and IPv6 over arbitrary topologies. If the tunnel mechanism does not decrement the TTL or Hop Limit of the network protocol carried within, the mechanism described in this document may be used to provide liveness detection for the tunnel. The BFD Authentication mechanism SHOULD be used and is strongly encouraged. 8. IANA Considerations Ports 3784 and 3875 were assigned by IANA for use with this protocol. 9. Security Considerations In this application, the use of TTL=255 on transmit and receive, coupled with an association to an incoming interface, is viewed as supplying equivalent security characteristics to other protocols used in the infrastructure, as it is not trivially spoofable. The security implications of this mechanism are further discussed in [GTSM]. The security implications of the use of BFD Authentication are discussed in [BFD]. The use of the TTL=255 check simultaneously with BFD Authentication provides a low overhead mechanism for discarding a class of unauthorized packets and may be useful in implementations in which cryptographic checksum use is susceptible to denial of service attacks. The use or non-use of this mechanism does not impact interoperability. Katz, Ward [Page 6] Internet Draft BFD for IPv4 and IPv6 (Single Hop) January, 2010 10. References 10.1. Normative References [BFD] Katz, D., and Ward, D., "Bidirectional Forwarding Detection", draft-ietf-bfd-base-10.txt, January, 2010. [BFD-GENERIC] Katz, D., and Ward, D., "Generic Application of BFD", draft-ietf-bfd-generic-05.txt, February, 2009. [GTSM] Gill, V., et al, "The Generalized TTL Security Mechanism (GTSM)", RFC 5082, October, 2007. [KEYWORD] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. 10.2. Informative References [BCP38] Ferguson, P, and Senie, D., "Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing", RFC 2827, May 2000. [TFRC] Floyd, S., et al, "TCP Friendly Rate Control (TFRC): Protocol Specification", RFC 5348, September, 2008. Authors' Addresses Dave Katz Juniper Networks 1194 N. Mathilda Ave. Sunnyvale, California 94089-1206 USA Phone: +1-408-745-2000 Email: firstname.lastname@example.org Dave Ward Juniper Networks 1194 N. Mathilda Ave. Sunnyvale, California 94089-1206 USA Phone: +1-408-745-2000 Email: email@example.com Katz, Ward [Page 7] Internet Draft BFD for IPv4 and IPv6 (Single Hop) January, 2010 Changes from the previous draft The applications section was clarified. This document expires in July, 2010. Katz, Ward [Page 8]