Internet DRAFT - draft-hegde-isis-link-overload
draft-hegde-isis-link-overload
IS-IS IGP S. Hegde
Internet-Draft P. Sarkar
Intended status: Standards Track H. Gredler
Expires: September 10, 2015 Juniper Networks, Inc.
March 9, 2015
ISIS Link Overload
draft-hegde-isis-link-overload-00
Abstract
Many ISIS deployments run on overlay networks provisioned by means of
pseudo-wires or L2-circuits. when the devices in the underlying
network go for maintenance, it is useful to divert the traffic away
from the specific node(s), to some alternate paths, before the
maintenance is actually scheduled. Since the nodes in the underlying
network are not visible to ISIS, existing Avoidance of traffic
blackhole mechanism described in [RFC3277] cannot be used. It is
useful for routers in IS-IS routing domain to be able to advertise a
link being in overload state to indicate impending maintenance
activity in the underlying network devices.
This document describes the protocol extensions to disseminate link
overload information in IS-IS protocol.
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
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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."
This Internet-Draft will expire on September 10, 2015.
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Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. ISIS Link overload bit . . . . . . . . . . . . . . . . . . . . 3
3. Elements of procedure . . . . . . . . . . . . . . . . . . . . . 3
3.1. Point-to-point links . . . . . . . . . . . . . . . . . . . 3
3.2. Broadcast links . . . . . . . . . . . . . . . . . . . . . . 4
4. Backward compatibility . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5
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1. Introduction
It is useful for routers in IS-IS routing domain to be able to
advertise a link being in overload state to indicate impending
maintenance activity on the link. This document provides mechanisms
to advertise link overload state in the Link attributes TLV as
defined in [RFC5029]
2. ISIS Link overload bit
The link-attribute sub-TLV is carried within the TLV 22 and has a
format identical to the sub-TLV format used by the Traffic
Engineering Extensions for IS-IS ([RFC3784]): 1 octet of sub-type, 1
octet of length of the value field of the sub-TLV followed by the
value field -- in this case, a 16 bit flags field.
The following bit represents the Link in overload.
Link Overload: 0x04 When set, this indicates that the link is
overloaded.
3. Elements of procedure
The Link attributes sub TLV with link-overload bit set indicates that
the Link which carries the sub TLV is overloaded. The node that has
the link going for maintenance, sets metric of the link to MAX-METRIC
and re-originates the LSP. The metric in the reverse direction also
need to change to divert the traffic from reverse direction. The
node SHOULD originate Link attributes sub TLV and set the overload
bit and originate the LSP and flood it in the respective IS-IS level.
When the originator of the Link attributes sub TLV, purges the LSP or
re-originates it without the Link Overload bit set, the metric on the
remote node SHOULD be changed back to the original value.
Based on the link type of the overloaded link, actions listed below
MAY be taken by the receiver.
3.1. Point-to-point links
When a link attributes sub TLV with link overload bit set is received
for a point-to-point link the receiver SHOULD identify the local link
which corresponds to the overloaded link and set the metric to MAX-
METRIC. Receiver node MUST re-originate the LSP with the changed
metric and flood into the ISIS level.
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3.2. Broadcast links
Broadcast networks in ISIS are represented by a star topology where
the Designated Intermediate System (DIS) is the central point to
which all other routers on the broadcast network connect. As a
result, routers on the broadcast network advertise only their
adjacency to the pseudo-node.As a result, routers on the broadcast
network advertise only their adjacency to the pseudo- node. Routers
that do not act as DIS do not advertise adjacencies with each other.
DIS originates pseudo-node which contains adjacenices with all the
neighbors. For the Broadcast links, the MAX-METRIC on the outgoing
link cannot be changed since all the adjacencies are on same link.
Setting the link cost to MAX- METRIC would impact paths going via all
neighbors.
When a link-attributes sub TLV with link-overload bit set is received
by the remote end for a broadcast link.
- If it's non DIS for that link, SHOULD not take any action.
- If receiving node is DIS for the link, it MUST set the metric from
the pseudo-node to the originator of the link overload bit to MAX-
METRIC and MUST re-originate the pseudo-node LSP and flood into the
ISIS Level.
4. Backward compatibility
The mechanism described in the document is fully backward
compatible.It is required that the originator and receiver of link-
overload bit understand the extensions defined in this document and
in case of broadcast links the originator and the DR need to
understand the extensions. Other nodes in the network compute based
on increased metric and hence the feature is backward compatible.
5. Security Considerations
This document does not introduce any further security issues other
than those discussed in [ISO10589] and [RFC1195].
6. IANA Considerations
This specification updates one ISIS registry: ISIS Link attributes
Sub TLV
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i) 0x04 - Link overload bit
7. Acknowledgements
8. References
8.1. Normative References
[ISO10589]
"Intermediate system to Intermediate system intra-domain
routeing information exchange protocol for use in
conjunction with the protocol for providing the
connectionless-mode Network Service (ISO 8473), ISO/IEC
10589:2002, Second Edition.", Nov 2002.
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3277] McPherson, D., "Intermediate System to Intermediate System
(IS-IS) Transient Blackhole Avoidance", RFC 3277,
April 2002.
[RFC3784] Smit, H. and T. Li, "Intermediate System to Intermediate
System (IS-IS) Extensions for Traffic Engineering (TE)",
RFC 3784, June 2004.
[RFC5029] Vasseur, JP. and S. Previdi, "Definition of an IS-IS Link
Attribute Sub-TLV", RFC 5029, September 2007.
8.2. Informative References
Authors' Addresses
Shraddha Hegde
Juniper Networks, Inc.
Embassy Business Park
Bangalore, KA 560093
India
Email: shraddha@juniper.net
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Pushpasis Sarkar
Juniper Networks, Inc.
Embassy Business Park
Bangalore, KA 560093
India
Email: psarkar@juniper.net
Hannes Gredler
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
US
Email: hannes@juniper.net
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