Network Working Group M. Bhatia, Ed.
Internet-Draft Alcatel-Lucent
Intended status: Standards Track M. Chen, Ed.
Expires: December 3, 2012 Huawei Technologies
S. Boutros, Ed.
M. Binderberger, Ed.
Cisco Systems
J. Haas, Ed.
Juniper Networks
June 1, 2012
Bidirectional Forwarding Detection (BFD) on Link Aggregation Group (LAG)
Interfaces
draft-mmm-bfd-on-lags-04
Abstract
This document proposes a mechanism to run BFD on Link Aggregation
Group (LAG) interfaces. It does so by running an independent
Asynchronous mode BFD session on every LAG member link.
This mechanism allows the verification of member link connectivity,
either in combination with, or in absence of, LACP. It provides a
shorter detection time than what LACP offers. The connectivity check
can also cover elements of layer 3 bidirectional forwarding.
This mechanism utilizes a well-known UDP port distinct from that of
single-hop BFD over IP. This new UDP port removes the ambiguity of
BFD over LAG packets from BFD over single-hop IP.
Requirements Language
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 [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
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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."
This Internet-Draft will expire on December 3, 2012.
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. BFD on LAG member links . . . . . . . . . . . . . . . . . . . . 4
2.1. Micro BFD session address family . . . . . . . . . . . . . 5
2.2. Micro BFD session negotiation . . . . . . . . . . . . . . . 5
3. LAG Management Module . . . . . . . . . . . . . . . . . . . . . 6
3.1. BFD in the presence of LACP . . . . . . . . . . . . . . . . 6
3.2. BFD in the absence of LACP . . . . . . . . . . . . . . . . 7
3.3. Handling Exceptions . . . . . . . . . . . . . . . . . . . . 7
4. BFD on LAG members and layer-3 applications . . . . . . . . . . 7
5. Detecting a member link failure . . . . . . . . . . . . . . . . 7
6. Security Consideration . . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
9. Contributing authors . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
The Bidirectional Forwarding Detection (BFD) protocol [RFC5880]
provides a mechanism to detect faults in the bidirectional path
between two forwarding engines, including interfaces, data link(s),
and to the extent possible the forwarding engines themselves, with
potentially very low latency. The BFD protocol also provides a fast
mechanism for detecting communication failures on any data links and
the protocol can run over any media and at any protocol layer.
Link aggregation (LAG) as defined in [IEEE802.1AX] provides
mechanisms to combine multiple physical links into a single logical
link. This logical link provides higher bandwidth and better
resiliency since if one of the physical member links fails the
aggregate logical link can continue to forward traffic over the
remaining operational physical member links.
Currently, the Link Aggregation Control Protocol (LACP) is used to
detect failures on a per physical member link. However, the use of
BFD for failure detection would (1) provide a faster detection (2)
provide detection in the absence of LACP (3) and would be able to
verify L3 connectivity per member link.
Running a single BFD session over the aggregation without internal
knowledge of the member links would make it impossible for BFD to
guarantee detection of the physical member link failures.
The goal is to verify link connectivity for every member link.
The approach taken in this document is to run a Asynchronous mode BFD
session over each member link and make BFD control whether the member
link should be part of the L2 Loadbalance table of the LAG virtual
port in the presence or the absence of LACP.
This document describes how to establish an Asynchronous mode BFD
session per physical member link of the LAG virtual port.
While there are native Ethernet mechanisms to detect failures
(802.1ax, .3ah) that could be used for LAG, the solution proposed in
this document enables operators who have already deployed BFD over
different technologies (e.g. IP, MPLS) to use a common failure
detection mechanism.
2. BFD on LAG member links
The mechanism proposed for a fast detection of LAG member link
failure is to run Asynchronous mode BFD sessions on every LAG member
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link. We call these per LAG member link BFD sessions "micro BFD
sessions" in the remainder of this document.
2.1. Micro BFD session address family
Only one address family MUST be used for all micro BFD sessions
running on all LAG member links. I.e. all member link micro BFD
sessions MUST either use IPv4 or IPv6.
2.2. Micro BFD session negotiation
A single micro BFD session runs on each member link of the LAG. The
micro BFD session's negotiation MUST follow the same procedures
defined in [RFC5880] and [RFC5881].
Only Asynchronous mode BFD is considered in this document; the use of
the BFD echo function is outside the scope of this document. At
least one system MUST take the Active role (possibly both). The
micro BFD sessions on the member links are independent BFD sessions:
They use their own unique local discriminator values, maintain their
own set of state variables and have their own independent state
machines. Timer values MAY be different, even among the micro BFD
sessions belonging to the same aggregation, although it is expected
that micro BFD sessions belonging to the same aggregation will use
the same timer values.
The demultiplexing of a received BFD packet is solely based on the
Your Discriminator field, if this field is nonzero. For the initial
Down BFD packets of a BFD session this value MAY be zero. In this
case demultiplexing MUST be based on some combination of other fields
which MUST include the interface information of the member link.
The procedure for the Reception of BFD Control Packets in Section
6.8.6 of [RFC5880] is amended as follows for per member link micro
BFD over LAG sessions: "If the Your Discriminator field is non-zero
and a micro BFD over LAG session is found, the interface on which the
micro BFD control packet arrived on MUST correspond to the interface
associated with that session."
The BFD Control packets for each micro BFD session are IP/UDP
encapsulated as defined in [RFC5881], but with a new UDP destination
port "BfdBndlPort" (to be assigned by IANA). Control packets use a
destination IP address that is the peer's remote IP address. The
details of how this destination IP address is learned is outside the
scope of this document.
On Ethernet-based LAG member links the destination MAC is a dedicated
MAC address (to be assigned by IANA according to [RFC5342]) to be the
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immediate next hop. This dedicated MAC address MUST be used for the
initial BFD packets of a micro BFD session when in the Down/AdminDown
state. When sending BFD packets for the micro BFD session in the
Init and Up state, the MAC address from the received BFD packets for
the session MUST be used.
On Ethernet-based LAG member links the source MAC SHOULD be the MAC
address of the port transmitting the packet.
This mechanism helps to reduce the use of additional MAC addresses,
which reduces the required resources on the Ethernet hardware on the
receiving port.
3. LAG Management Module
The LAG Management Module (LMM) could be envisaged as a client of
BFD; i.e. the LMM requests a micro BFD session per member link. The
LMM then uses the micro BFD session state, in addition to LACP state,
to monitor the health of the individual members links of the LAG.
The micro BFD session for a particular port MUST be requested when
the port is attached to an aggregator. The session MUST be deleted
when the port is detached from the aggregator.
The LMM uses the status of the BFD session to determine whether the
member link should be included in the LAG L2 load balance table. In
other words, even when LACP is used and considers the member link to
be ready to forward traffic, the member link is only used by the
traffic load balancer when the micro BFD session is Up.
3.1. BFD in the presence of LACP
Prior to LACP coming up, the micro BFD session is Passive and does
not send BFD control packets. Once LACP has determined that a link
is suitable for aggregation within its selected LAG and has completed
negotiations with the partner device so as to bring that link to
Distributing state, the micro BFD session can be made Active and the
session started on the link.
BFD, as a layer 3 protocol, is viewed as running across the LAG, with
load balancing constraints ensuring particular BFD micro sessions are
effectively bound to particular member links.
Although the link is in LACP Distributing state, it should not be
used for carrying traffic other than the micro BFD session. BFD is
used to verify that a link is ready to be an active member of its LAG
for the purpose of carrying LAG level data traffic. Only when the
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micro BFD session is up should the link become active for forwarding
general traffic over the bundle.
3.2. BFD in the absence of LACP
Use of LACP for link aggregation is strictly optional. It is equally
possible to use no aggregation control protocol and to step directly
from the layer 1 or layer 2 OAM state becoming operational to
starting the micro BFD session. In this case, the micro BFD sessions
begin as Active.
3.3. Handling Exceptions
If the BFD over LAG feature were provisioned on an aggregated link
member after the link was already active within a LAG, BFD session
state SHOULD NOT influence link state until the BFD session state
transitions to Up. If the BFD session never transitions to Up but
the LAG becomes inactive, the previously documented procedures would
then normally apply.
If the BFD over LAG feature were deprovisioned on an aggregate link
member after the BFD session had transitioned to Up, BFD may indicate
to the remote port that it should not take the port down or remove it
from the aggregation by setting its BFD session state to AdminDown.
Note that if one device is not operating a micro BFD session on a
link, while the other device is and perceives the session to be Down,
this will result in the two devices having a different view of the
status of the link. This would likely lead to traffic loss across
the LAG.
The use of another protocol to bootstrap BFD can detect such
mismatched config, since the side that's not configured can send a
rejection error. Such bootstrapping mechanisms are outside the scope
of this document.
4. BFD on LAG members and layer-3 applications
Layer 3 protocols, e.g. OSPF, may use a micro BFD session to detect
failures on the LAG virtual port, or may establish a new BFD session
over the logical LAG virtual port.
5. Detecting a member link failure
When a micro BFD session goes down then this member link MUST be
taken out of the LAG L2 load balance table.
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6. Security Consideration
This document does not introduce any additional security issues and
the security mechanisms defined in [RFC5880] apply in this document.
7. IANA Considerations
The IANA is requested to assign a well-known port number for the UDP
encapsulated micro BFD sessions. IANA is also requested to assign a
dedicated MAC address according to RFC 5342 [RFC5342].
8. Acknowledgements
We would like to thank Dave Katz, Alexander Vainshtein, Greg Mirsky
and Jeff Tantsura for their comments.
The initial event to start the current discussion was the
distribution of draft-chen-bfd-interface-00.
9. Contributing authors
Paul Hitchen
BT
Email: paul.hitchen@bt.com
George Swallow
Cisco Systems
Email: swallow@cisco.com
Wim Henderickx
Alcatel-Lucent
Email: wim.henderickx@alcatel-lucent.com
Nobo Akiya
Cisco Systems
Email: nobo@cisco.com
Neil Ketley
Cisco Systems
Email: nketley@cisco.com
Carlos Pignataro
Cisco Systems
Email: cpignata@cisco.com
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Nitin Bahadur
Juniper Networks
Email: nitinb@juniper.net
Zuliang Wang
Huawei Technologies
Email: liang_tsing@huawei.com
Liang Guo
China Telecom
Email: guoliang@gsta.com
Jeff Tantsura
Ericsson
Email: jeff.tantsura@ericsson.com
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, June 2010.
[RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
June 2010.
10.2. Informative References
[IEEE802.1AX]
IEEE Std. 802.1AX, "IEEE Standard for Local and
metropolitan area networks - Link Aggregation",
November 2008.
[RFC5342] Eastlake, D., "IANA Considerations and IETF Protocol Usage
for IEEE 802 Parameters", BCP 141, RFC 5342,
September 2008.
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Authors' Addresses
Manav Bhatia (editor)
Alcatel-Lucent
Bangalore 560045
India
Email: manav.bhatia@alcatel-lucent.com
Mach(Guoyi) Chen (editor)
Huawei Technologies
Q14 Huawei Campus, No. 156 Beiqing Road, Hai-dian District
Beijing 100095
China
Email: mach@huawei.com
Sami Boutros (editor)
Cisco Systems
Email: sboutros@cisco.com
Marc Binderberger (editor)
Cisco Systems
Email: mbinderb@cisco.com
Jeffrey Haas (editor)
Juniper Networks
Email: jhaas@juniper.net
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