Internet DRAFT - draft-ietf-bfd-on-lags
draft-ietf-bfd-on-lags
Network Working Group M. Bhatia, Ed.
Internet-Draft Alcatel-Lucent
Intended status: Standards Track M. Chen, Ed.
Expires: June 21, 2014 Huawei Technologies
S. Boutros, Ed.
M. Binderberger, Ed.
Cisco Systems
J. Haas, Ed.
Juniper Networks
December 18, 2013
Bidirectional Forwarding Detection (BFD) on Link Aggregation Group (LAG)
Interfaces
draft-ietf-bfd-on-lags-04
Abstract
This document defines 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 continuity,
either in combination with, or in absence of, Link Aggregation
Control Protocol (LACP). It provides a shorter detection time than
what LACP offers. The continuity check can also cover elements of
layer 3 bidirectional forwarding.
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
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."
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This Internet-Draft will expire on June 21, 2014.
Copyright Notice
Copyright (c) 2013 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
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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 Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. BFD on LAG member links . . . . . . . . . . . . . . . . . . . 5
2.1. Micro BFD session address family . . . . . . . . . . . . . 5
2.2. Micro BFD session negotiation . . . . . . . . . . . . . . 5
2.3. Micro BFD session Ethernet details . . . . . . . . . . . . 6
3. Interaction between LAG and BFD . . . . . . . . . . . . . . . 7
4. BFD on LAG member links 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 . . . . . . . . . . . . . . . . . . 10
Appendix A. Considerations when using BFD on member links . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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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 the ability for each member link to be able to forward L3
packets.
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 Continuity for every member link. This
corresponds to [RFC5882], section 7.3.
The approach taken in this document is to run a Asynchronous mode BFD
session over each LAG member link and make BFD control whether the
LAG member link should be part of the L2 Loadbalance table of the LAG
interface in the presence or the absence of LACP.
This document describes how to establish an Asynchronous mode BFD
session per physical LAG member link of the LAG interface.
While there are native Ethernet mechanisms to detect failures
(802.1ax, .3ah) that could be used for LAG, the solution defined in
this document enables operators who have already deployed BFD over
different technologies (e.g. IP, MPLS) to use a common failure
detection mechanism.
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2. BFD on LAG member links
The mechanism defined for a fast detection of LAG member link failure
is to run Asynchronous mode BFD sessions on every LAG member 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
Member link micro BFD sessions, when using IP/UDP encapsulation, can
use IPv4 or IPv6 addresses. Two micro sessions MAY exist per member
link, one IPv4, another IPv6. When an address family is used on one
member link then it MUST be used on all member links of the
particular LAG.
2.2. Micro BFD session negotiation
A single micro BFD session for every enabled address family 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 and
the destination UDP port of the received BFD packet.
The procedure for the Reception of BFD Control Packets in Section
6.8.6 of [RFC5880] is amended as follows for per LAG member link
micro BFD 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."
This document defines the BFD Control packets for each micro BFD
session to be IP/UDP encapsulated as defined in [RFC5881], but with a
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new UDP destination port 6784.
The new UDP port removes the ambiguity of BFD over LAG packets from
BFD over single-hop IP. An example is (mis-)configuring a LAG with
micro BFD sessions on one side but using a [RFC5881] BFD session for
the LAG (treated as a single interface) on the opposite side.
The procedures in this document MUST be used for BFD messages
addressed to port 6784 and MUST NOT be used for others ports assigned
in RFCs described other BFD modes.
Control packets use a destination IP address that is configured on
the peer system and can be reached via the LAG interface.
Implementations may range from explicitly configuring IP addresses
for the BFD sessions to out-of-band methods for learning the
destination IP address. The details are outside the scope of this
document.
2.3. Micro BFD session Ethernet details
On Ethernet-based LAG member links the destination MAC is the
dedicated multicast MAC address 01-00-5E-90-00-01 to be the 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 and
Init state. When a micro BFD session is changing into Up state then
the first bfd.DetectMult packets with Up state MUST be sent with the
dedicated MAC. For the following BFD packets with Up state the
source MAC address from the received BFD packets for the session MAY
be used instead of the dedicated MAC.
All implementations MUST be able to send and receive BFD packets in
Up state using the dedicated MAC address. Implementations supporting
both, sending BFD Up packets with the dedicated and the received MAC,
need to offer means to control the behaviour.
On Ethernet-based LAG member links the source MAC SHOULD be the MAC
address of the member link 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 member link.
Micro BFD packets SHOULD always be sent untagged. However, when the
LAG is operating in the context of IEEE 802.1q or IEEE 802.qinq, the
micro BFD packets may either be untagged or sent with a vlan tag of
Zero (802.1p priority tagged). Implementations compliant to this
standard MUST be able to receive both untagged and 802.1p priority
tagged micro BFD packets.
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3. Interaction between LAG and BFD
The micro BFD sessions for a particular LAG member link MUST be
requested when a member link state is either Distributing or Standby.
The sessions MUST be deleted when the member link is neither in
Distributing nor in Standby state anymore.
BFD is used to control if the load balance algorithm is able to
select a particular LAG member link. In other words, even when Link
Aggregation Control Protocol (LACP) is used and considers the member
link to be ready to forward traffic, the member link MUST NOT be used
by the load balancer until all the micro BFD sessions of the
particular member link are in Up state.
In case an implementation has separate load balance tables for IPv4
and IPv6 and if both an IPv4 and IPv6 micro session exist for a
member link then an implementation MAY enable the member link in the
load balance algorithm based on the BFD session with a matching
address family alone.
An exception is the BFD packet itself. Implementations MAY receive
and transmit BFD packets via the Aggregator's MAC service interface
independent of the session state.
4. BFD on LAG member links and layer-3 applications
The mechanism described in this document is likely to be used by
modules managing Interfaces or Link aggregation groups and thus
managing the member links of a LAG. Typical layer 3 protocols like
OSPF do not have an insight into the LAG and treat it as one bigger
interface. The signaling from micro sessions to layer 3 protocols is
effectively done by the impact of BFD micro sessions on the load
balance table and the Interface/LAG managing module's potential
decision to shut down the LAG. An active method to test the impact
of micro sessions is for layer 3 protocols to request a single BFD
session per LAG.
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(s).
In case an implementation has separate load balance tables for IPv4
and IPv6 then if both an IPv4 and IPv6 micro session exist for a
member link an implementation MAY remove the member link only from
the load balance table that matches the address family of the failing
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BFD session. For example the IPv4 micro session fails but the IPv6
micro session stays Up then the member link MAY be removed from only
the IPv4 load balance table; the link MAY remain in the IPv6 load
balancing table. Alternatively, the member link may be removed from
both the IPv4 and IPv6 load balancing tables. This decision is an
implementation detail.
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
IANA assigned a dedicated MAC address 01-00-5E-90-00-01 (see
[RFC7042]) as well as UDP port 6784 for Bidirectional Forwarding
Detection (BFD) on Link Aggregation Group (LAG) Interfaces. IANA is
requested to change the reference to [RFC-to-be].
IANA is requested to change the registry for port 6784 to show the
Assignee as [IESG] and the Contact as [BFD Chairs]. The expansion of
[BFD Chairs] should be shown as "mailto:bfd-chairs@tools.ietf.org".
IANA is requested to change the reference to [RFC-to-be].
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
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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
Nitin Bahadur
Bracket Computing
Email: nitin@brkt.com
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.
[RFC5882] Katz, D. and D. Ward, "Generic Application of
Bidirectional Forwarding Detection (BFD)", RFC 5882,
June 2010.
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10.2. Informative References
[IEEE802.1AX]
IEEE Std. 802.1AX, "IEEE Standard for Local and
metropolitan area networks - Link Aggregation",
November 2008.
[RFC7042] Eastlake, D. and J. Abley, "IANA Considerations and IETF
Protocol and Documentation Usage for IEEE 802 Parameters",
BCP 141, RFC 7042, October 2013.
Appendix A. Considerations when using BFD on member links
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 the load balance algorithm 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.
This procedure ensures that the sequence of events - enabling the LAG
and enabling BFD on the LAG - has no impact on the forwarding
service.
If the BFD over LAG feature was deprovisioned on an aggregate link
member while the associated micro BFD session was in Up state, BFD
should transition its state to AdminDown and should attempt to
communicate this state change to the peer.
If the local or the remote state of a micro BFD session is AdminDown
the system should not indicate a connectivity failure to any client
and should not remove the particular LAG member link from forwarding.
This behaviour is independent from the use of Link Aggregation
Control Protocol (LACP) for the LAG.
When traffic is forwarded across a link while the corresponding micro
BFD session is not in Up state an implementation may use a
configurable timeout value after which the BFD session must have
reached Up state or otherwise the link is taken out of forwarding.
When such timeout values exist then the configuration must allow to
turn off the timeout function.
The configurable timeout value shall ensure that a LAG is not
remaining forever in an "inconsistent" state where forwarding occurs
on a link with no confirmation from the micro BFD session that the
link is healthy.
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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.
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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