IS-IS WG S. Hegde
Internet-Draft C. Bowers
Intended status: Standards Track Juniper Networks
Expires: February 17, 2017 P. Mattes
M. Nanduri
Microsoft
I. Mohammad
Arista Networks
August 16, 2016
Advertising TE protocols in IS-IS
draft-hegde-isis-advertising-te-protocols-00
Abstract
This document defines a mechanism to indicate which traffic
engineering protocols are enabled on a link in IS-IS. It does so by
introducing a new traffic-engineering protocol sub-TLV for TLV-22.
This document also describes mechanisms to address backward
compatibility issues for implementations that have not yet been
upgraded to software that understands this new sub-TLV.
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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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 17, 2017.
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Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Traffic-engineering protocol sub-TLV . . . . . . . . . . 4
4. Backward compatibility . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
IS-IS extensions for traffic engineering are specified in [RFC5305].
[RFC5305] defines several link attributes such as administrative
group, maximum link bandwidth, and shared risk link groups (SRLGs)
which can be used by traffic engineering applications. Additional
link attributes for traffic engineering have subsequently been
defined in other documents as well. Most recently [RFC7810] defined
link attributes for delay, loss, and measured bandwidth utilization.
The primary consumers of these traffic engineering link attributes
have been RSVP-based applications that use the advertised link
attributes to compute paths which will subsequently be signalled
using RSVP-TE. However, these traffic engineering link attributes
have also been used by other applications, such as IP/LDP fast-
reroute using loop-free alternates as described in [RFC7916]. In the
future, it is likely that traffic engineering applications based on
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Segment Routing [I-D.ietf-spring-segment-routing] will also use these
link attributes.
Existing IS-IS standards do not provide a mechanism to explicitly
indicate whether or not RSVP has been enabled on a link. Instead,
different RSVP-TE implementations have used the presence of certain
traffic engineering sub-TLVs in IS-IS to infer that RSVP signalling
is enabled on a given link. A study was conducted with various
vendor implementations to determine which traffic engineering sub-
TLVs cause an implementation to infer that RSVP signalling is enabled
on a link. The results are shown in Figure 1.
+--------+--------------------------------------------+
| TLV/ | Sub-TLV name | X | Y | Z |
|sub-TLV | | | | |
+--------+--------------------------------------------+
|22 |Extended IS Reachability TLV | N | N | N |
|22/3 |Administrative group (color) | N | Y | Y |
|22/4 |Link Local/Remote ID | N | N | N |
|22/6 |IPV4 Interface Address | N | N | N |
|22/8 |IPV4 Neighbor Address | N | N | N |
|22/9 |Max Link Bandwidth | N | Y | Y |
|22/10 |Max Reservable Link Bandwidth| N | Y | Y |
|22/11 |Unreserved Bandwidth | Y | Y | Y |
|22/14 |Extended Admin Group | N | Y | N |
|22/18 |TE Default Metric | N | N | N |
|22/20 |Link Protection Type | N | Y | Y |
|22/21 |Interface Switching | N | Y | Y |
| | Capability | | | |
|22/22 |TE Bandwidth Constraints | N | Y | Y |
|22/33-39|TE Metric Extensions(RFC7180)| N | N | N |
|138 |SRLG TLV | N | Y | Y |
+--------+--------------------------------------------+
Figure 1: Traffic engineering Sub-TLVs that cause implementation X,
Y, or Z to infer that RSVP signalling is enabled on a link
The study indicates that the different implementations use the
presence of different sub-TLVs under TLV 22 (or the presence of TLV
138) to infer that RSVP signalling is enabled on a link. It is
possible that other implementations may use other sub-TLVs to infer
that RSVP is enabled on a link.
This document defines a standard way to indicate whether or not RSVP,
segment routing, or another future protocol is enabled on a link. In
this way, implementations will not have to infer whether or not RSVP
is enabled based on the presence of different sub-TLVs, but can use
the explicit indication. When network operators want to use a non-
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RSVP traffic engineering application (such as IP/LDP FRR or segment
routing), they will be able to advertise traffic engineer sub-TLVs
and explicitly indicate what traffic engineering protocols are
enabled on a link.
2. Motivation
The motivation of this document is to provide a mechanism to
advertise TE attributes for current and future applications without
ambiguity. The following objectives help to accomplish this in a
range of deployment scenarios.
1. Advertise TE attributes for the link for variety of applications.
2. Allow the solution to be backward compatible so that nodes that
do not understand the new advertisement do not cause issues for
existing RSVP deployment.
3. Allow the solution to be extensible for any new applications that
need to look at TE attributes.
3. Solution
3.1. Traffic-engineering protocol sub-TLV
A new sub-TLV Traffic-engineering protocol sub-TLV is added in the
TLV 22 [RFC5305] or TLV 222 to indicate the protocols enabled on the
link. The sub-TLV has flags in the value field to indicate the
protocol enabled on the link. The length field is variable to allow
the flags field to grow for future requirements.
Type : TBD suggested value 40
Length: Variable
Value :
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Traffic-Engineering Protocol sub-TLV
Type : TBA (suggested value 40)
Length: variable (in bytes)
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Value: The value field consists of bits indicating the protocols
enabled on the link. This document defines the two protocol values
below.
+----------+-------------------------------+
| Value | Protocol Name |
+----------+-------------------------------+
|0x01 | RSVP |
+----------+-------------------------------+
|0x02 | Segment Routing |
+----------+-------------------------------+
Figure 3: Flags for the protocols
The RSVP flag is set to one to indicate that RSVP-TE is enabled on a
link. The RSVP flag is set to zero to indicate that RSVP-TE is not
enabled on a link.
The Segment Routing flag is set to one to indicate that Segment
Routing is enabled on a link. The Segment Routing flag is set to
zero to indicate that Segment Routing is not enabled on a link.
All undefined flags MUST be set to zero on transmit and ignored on
receipt.
An implementation that supports the TE protocol sub-TLV and sends TLV
22 MUST advertise the TE protocol sub-TLV in TLV 22 for that link,
even when both the RSVP and SR flags are set to zero. This allows a
receiving router to determine whether or not the sending router is
capable of sending the TE protocol sub-TLV. It is used for backward
compatibility as described in Section 4.
4. Backward compatibility
Routers running older software that do not understand the new
Traffic-Engineering protocol sub-TLV will continue to interpret the
presence of some sub-TLVs in TLV 22 or the presence of TLV 138 as
meaning that RSVP is enabled a link. A network operator may not want
to or be able to upgrade all routers in the domain at the same time.
There are two backward compatibility scenarios to consider depending
on whether the router that doesn't understand the new TE protocol
sub-TLV is an RSVP-TE ingress router or an RSVP-TE transit router.
Suppose we have an upgraded transit router that explicitly indicates
that RSVP is not enabled on a link by advertising the TE protocol
sub-TLV with the RSVP flag set to zero. An RSVP-TE ingress router
that has not been upgraded to understand the new TE protocol sub-TLV
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will not understand that RSVP-TE is not enabled on the link, and may
include the link on a path computed for RSVP-TE. When the network
tries to signal an explicit path LSP using RSVP-TE through that link,
it will fail. In order to avoid this scenario, an operator can use
the mechanism described below.
For this scenario, the basic idea is to use the existing
administrative group link attribute as a means of preventing existing
RSVP implementations from using a link. The network operator defines
an administrative group to mean that RSVP is not enabled on a link.
We call this admin group the RSVP-not-enabled admin group. If the
operator needs to advertise a TE sub-TLV (maximum link bandwidth, for
example) on a link, but doesn't want to enable RSVP on that link,
then the operator also advertises the RSVP-not-enabled admin group on
that link. The operator can then use existing mechanisms to exclude
links advertising the RSVP-not-enabled admin group from the
constrained shortest path first (CSPF) computation used by RSVP.
This will prevent RSVP implementations from attempting to signal
RSVP-TE LSPs across links that do not have RSVP enabled. Once the
entire network domain is upgraded to understand the TE protocol sub-
TLV in this draft, the configuration involving the RSVP-not-enabled
admin group is no longer needed for this network.
The other scenario to consider is when the RSVP-TE ingress router has
been upgraded to understand the TE protocol sub-TLV, but an RSVP-TE
transit router has not. In this case, the transit router is not
capable of sending the TE protocol sub-TLV. If the RSVP-TE ingress
router understands that the transit router is not capable of sending
the TE protocol sub-TLV, then it can continue inferring whether or
not RSVP-TE is enabled on the transit router links based on the
presence of TE sub-TLVs, as it does today. We require an upgraded
router to send the TE protocol sub-TLV if it sends TLV 22, even when
both the RSVP and SR flags are set to zero. This allows the
receiving router to interpret the absence of the TE-protocol sub-TLV
together with presence of TLV 22 to mean that the sending router has
not been upgraded. This allows the upgraded RSVP-TE ingress router
to distingish between transit routers that have been upgraded and
those that haven't, and behave accordingly.
5. Security Considerations
This document does not introduce any further security issues other
than those discussed in [RFC1195] and [RFC5305].
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6. IANA Considerations
This specification updates one IS-IS registry:
The extended IS reachability TLV Registry
i) Traffic-engineering Protocol sub-tlv = Suggested value 40
7. Acknowledgements
The authors thank Alia Atlas and Les Ginsberg for helpful discissions
on the topic of this draft.
8. References
8.1. Normative References
[I-D.ietf-spring-segment-routing]
Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
and R. Shakir, "Segment Routing Architecture", draft-ietf-
spring-segment-routing-09 (work in progress), July 2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <http://www.rfc-editor.org/info/rfc5305>.
[RFC7810] Previdi, S., Ed., Giacalone, S., Ward, D., Drake, J., and
Q. Wu, "IS-IS Traffic Engineering (TE) Metric Extensions",
RFC 7810, DOI 10.17487/RFC7810, May 2016,
<http://www.rfc-editor.org/info/rfc7810>.
8.2. Informative References
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, DOI 10.17487/RFC1195,
December 1990, <http://www.rfc-editor.org/info/rfc1195>.
[RFC7916] Litkowski, S., Ed., Decraene, B., Filsfils, C., Raza, K.,
Horneffer, M., and P. Sarkar, "Operational Management of
Loop-Free Alternates", RFC 7916, DOI 10.17487/RFC7916,
July 2016, <http://www.rfc-editor.org/info/rfc7916>.
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Authors' Addresses
Shraddha Hegde
Juniper Networks
Embassy Business Park
Bangalore, KA 560093
India
Email: shraddha@juniper.net
Chris Bowers
Juniper Networks
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
US
Email: cbowers@juniper.net
Paul Mattes
Microsoft
One Microsoft Way
Redmond, WA 98052
US
Email: pamattes@microsoft.com
Mohan Nanduri
Microsoft
One Microsoft Way
Redmond, WA 98052
US
Email: mnanduri@microsoft.com
Imtiyaz Mohammad
Arista Networks
Global Tech Park
Bangalore, KA 560103
India
Email: imtiyaz@arista.com
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