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IETF RFC 7917
Last modified on Tuesday, July 12th, 2016
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Internet Engineering Task Force (IETF) P. Sarkar, Ed.
Request for Comments: 7917 Individual Contributor
Category: Standards Track H. Gredler
ISSN: 2070-1721 RtBrick Inc.
S. Hegde
Juniper Networks, Inc.
S. Litkowski
B. Decraene
Orange
July 2016
Advertising Node Administrative Tags in IS-IS
 Abstract
This document describes an extension to the IS-IS routing protocol to
advertise node administrative tags. This optional capability allows
tagging and grouping of the nodes in an IS-IS domain. The node
administrative tags can be used to express and apply locally defined
network policies, thereby providing a very useful operational
capability. Node administrative tags may be used by either IS-IS
itself or other applications consuming information propagated via IS-
IS.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/RFC 7917.
Sarkar, et al. Standards Track PAGE 1 
RFC 7917 Node Administrative Tags in IS-IS July 2016
Copyright Notice
Copyright (c) 2016 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 Simplified BSD License.
Table of Contents
1. Introduction ....................................................3
1.1. Requirements Language ......................................3
2. Node Administrative Tags ........................................3
3. Node Administrative Tag (Node-Admin-Tag) Sub-TLV ................3
3.1. TLV Format .................................................4
4. Elements of Procedure ...........................................5
4.1. Interpretation of Node Administrative Tags .................5
4.2. Use of Node Administrative Tags ............................5
4.3. Processing Node Administrative Tag Changes .................6
5. Applications ....................................................7
6. Security Considerations .........................................7
7. Operational Considerations ......................................8
8. Manageability Considerations ....................................8
9. IANA Considerations .............................................8
10. References .....................................................9
10.1. Normative References ......................................9
10.2. Informative References ....................................9
Acknowledgments ...................................................11
Contributors ......................................................11
Authors' Addresses ................................................11
Sarkar, et al. Standards Track PAGE 2
RFC 7917 Node Administrative Tags in IS-IS July 2016
1. Introduction
It is useful to assign a node administrative tag to a router in the
IS-IS domain and use it as an attribute associated with the node.
The node administrative tag can be used in variety of applications.
For example:
(a) Traffic-engineering applications to provide different
path-selection criteria.
(b) Preference for, or pruning of, certain paths in Loop-Free
Alternate (LFA) [RFC 5286] backup selection via local policies as
defined in [RFC 7916].
This document provides mechanisms to advertise node administrative
tags in IS-IS for various applications, including (but not limited
to) route and path selection. Route and path selection functionality
applies to both Traffic Engineering (TE) and non-TE applications.
Hence, the new sub-TLV for carrying node administrative tags is
included in the Router CAPABILITY TLV [RFC 4971].
1.1. 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 [RFC 2119].
2. Node Administrative Tags
An administrative tag is a 32-bit unsigned integer value that can be
used to identify a group of nodes in the IS-IS domain. An IS-IS
router should advertise in the specific IS-IS level the set of groups
of which it is a part.
As an example, all edge network devices in a given network may be
configured with a certain tag value, whereas all core network devices
may be configured with another, different tag value.
3. Node Administrative Tag (Node-Admin-Tag) Sub-TLV
The new sub-TLV defined in this document is carried within an IS-IS
Router CAPABILITY TLV (IS-IS TLV type 242) [RFC 4971] in the Link
State PDUs originated by the device. Router CAPABILITY TLVs
[RFC 4971] can have "level-wide" or "domain-wide" flooding scope. The
choice of flooding scope in which a specific node administrative tag
shall be flooded is purely a matter of local policy and is defined by
the operator's usage needs. An operator MAY choose to advertise a
set of node administrative tags across levels and another different
Sarkar, et al. Standards Track PAGE 3
RFC 7917 Node Administrative Tags in IS-IS July 2016
set of node administrative tags within the specific level.
Alternatively, the operator may use the same node administrative tags
within both the "domain-wide" flooding scope and one or more
"level-wide" flooding scopes.
The format of the Node Administrative Tag (Node-Admin-Tag) sub-TLV
(see Section 3.1) does not include a topology identifier. Therefore,
it is not possible to indicate a topology-specific context when
advertising node administrative tags. Hence, in deployments using
multi-topology routing [RFC 5120], advertising a separate set of node
administrative tags for each topology SHOULD NOT be supported.
3.1. TLV Format
[RFC 4971] defines the Router CAPABILITY TLV, which may be used to
advertise properties of the originating router. The payload of
the Router CAPABILITY TLV consists of one or more nested
Type-Length-Value (TLV) triplets.
The new Node-Admin-Tag sub-TLV, like other IS-IS sub-TLVs, is
formatted as TLV triplets. Figure 1 below shows the format of the
new sub-TLV.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Administrative Tag #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Administrative Tag #2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Administrative Tag #N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 21 (Node-Admin-Tag)
Length: An 8-bit field that indicates the length of the Value
portion in octets; this will be a multiple of 4 octets,
depending on the number of tags advertised.
Value: Defines the node administrative tags (Administrative Tag #1,
Administrative Tag #2, etc.). Multiples of 4 octets.
Figure 1: IS-IS Node-Admin-Tag Sub-TLV
Sarkar, et al. Standards Track PAGE 4
RFC 7917 Node Administrative Tags in IS-IS July 2016
4. Elements of Procedure
4.1. Interpretation of Node Administrative Tags
The meaning of node administrative tags is generally opaque to IS-IS.
A router advertising one or more node administrative tags may be
configured to do so without knowing (or even explicitly supporting)
the functionality implied by the tag. This section describes general
rules, regulations, and guidelines for using and interpreting a node
administrative tag; these rules, regulations, and guidelines will
facilitate interoperable implementations between vendors.
Interpretation of tag values is specific to the administrative domain
of a particular network operator. Hence, tag values SHOULD NOT be
propagated outside the administrative domain to which they apply.
The meaning of a node administrative tag is defined by the network
local policy and is controlled via configuration. If a receiving
node does not understand the tag value, it ignores the specific tag
and floods the Router CAPABILITY TLV without any change, as defined
in [RFC 4971].
The semantics of the tag order has no meaning. There is no implied
meaning to the ordering of the tags that indicates a certain
operation or set of operations that need to be performed based on the
ordering.
Each tag SHOULD be treated as an independent identifier that may be
used in a policy to perform a policy action. Each tag carried by the
Node-Admin-Tag sub-TLVs should be used to indicate a characteristic
of a node that is independent of the characteristics indicated by
other administrative tags within the same instance or another
instance of a Node-Admin-Tag sub-TLV. The list of node
administrative tags carried in a Node-Admin-Tag sub-TLV MUST be
considered as an unordered list. Whilst policies may be implemented
based on the presence of multiple tags (e.g., if tag A AND tag B are
present), they MUST NOT be reliant upon the order of the tags (i.e.,
all policies should be considered commutative operations, such that
tag A preceding or following tag B does not change their outcome).
4.2. Use of Node Administrative Tags
The node administrative tags are not meant to be extended by future
IS-IS standards. New IS-IS extensions are not expected to require
the use of node administrative tags or define well-known tag values.
Node administrative tags are for generic use and do not require IANA
registration. Future IS-IS extensions requiring well-known values
MAY define their own data signaling tailored to the needs of the
feature or MAY use the Router CAPABILITY TLV as defined in [RFC 4971].
Sarkar, et al. Standards Track PAGE 5
RFC 7917 Node Administrative Tags in IS-IS July 2016
Node administrative tags are expected to be associated with a stable
attribute. In particular, node administrative tags MUST NOT be
associated with something whose state can oscillate frequently, e.g.,
the reachability of a specific destination.
While no specific limit on the number of node administrative tags
that may be advertised has been defined, it is expected that only a
modest number of tags will be required in any deployment.
4.3. Processing Node Administrative Tag Changes
Multiple Node-Admin-Tag sub-TLVs MAY appear in a Router CAPABILITY
TLV, or Node-Admin-Tag sub-TLVs MAY be contained in different
instances of Router CAPABILITY TLVs. The node administrative tags
associated with a node that originates tags for the purpose of any
computation or processing at a receiving node SHOULD be a superset of
node administrative tags from all the TLVs in all the instances of
Router CAPABILITY TLVs received in the Link State PDU(s) advertised
by the corresponding IS-IS router. When a Router CAPABILITY TLV is
received that changes the set of node administrative tags applicable
to any originating node, a receiving node MUST repeat any computation
or processing that makes use of node administrative tags.
When there is a change to, or removal of, an administrative
affiliation of a node, the node MUST re-originate the Router
CAPABILITY TLV(s) with the latest set of node administrative tags.
On a receiving router, on detecting a change in contents (or removal)
of existing Node-Admin-Tag sub-TLV(s) or the addition of new
Node-Admin-Tag sub-TLV(s) in any instance of Router CAPABILITY
TLV(s), implementations MUST take appropriate measures to update
their state according to the changed set of node administrative tags.
The exact actions needed will vary, depending on what features are
associated with node administrative tags; this topic is outside the
scope of this specification.
Sarkar, et al. Standards Track PAGE 6
RFC 7917 Node Administrative Tags in IS-IS July 2016
5. Applications
[RFC 7777] lists several non-normative examples of how implementations
might use node administrative tags. These examples are given only to
demonstrate the generic usefulness of the router tagging mechanism.
An implementation supporting this specification is not required to
implement any of the use cases. The following is a brief list of
non-normative use cases listed in [RFC 7777]. Please refer to
Section 3 of [RFC 7777] for more details.
1. Auto-discovery of services
2. Policy-based Fast Reroute (FRR)
(a) Administrative limitation of LFA scope
(b) Optimizing LFA calculations
3. Controlling remote LFA tunnel termination
4. Mobile backhaul network service deployment
5. Policy-based explicit routing
6. Security Considerations
This document does not introduce any new security issues. Node
administrative tags, like link administrative tags (a.k.a.
administrative groups) [RFC 5305], can be used by operators to
indicate geographical location or other sensitive information. The
information carried in node administrative tags, like link
administrative tags, can be leaked to an IGP snooper.
Advertisement of tag values for one administrative domain into
another involves the risk of misinterpretation of the tag values (if
the two domains have assigned different meanings to the same values)
and may have undesirable and unanticipated side effects.
Security concerns for IS-IS are already addressed in [ISO10589],
[RFC 5304], and [RFC 5310] and are applicable to the mechanisms
described in this document. Extended authentication mechanisms
described in [RFC 5304] or [RFC 5310] SHOULD be used in deployments
where attackers have access to the physical networks, because nodes
included in the IS-IS domain are vulnerable.
Sarkar, et al. Standards Track PAGE 7
RFC 7917 Node Administrative Tags in IS-IS July 2016
7. Operational Considerations
Operators can assign a meaning to the node administrative tags that
is local to the operator's administrative domain. The operational
use of node administrative tags is analogical to the IS-IS prefix
tags [RFC 5130] and BGP communities [RFC 1997]. Operational discipline
and procedures followed in configuring and using BGP communities and
IS-IS prefix tags are also applicable to the usage of node
administrative tags.
Defining a language for local policies is outside the scope of this
document. As is the case with other policy applications, the pruning
policies can cause the path to be completely removed from the
forwarding plane and hence have the potential for a more severe
impact on operations (e.g., node unreachability due to path removal)
as compared to preference policies that only affect path selection.
8. Manageability Considerations
Node administrative tags are configured and managed using routing
policy enhancements. YANG [RFC 6020] is a data modeling language used
to specify configuration data models. The IS-IS YANG data model is
described in [YANG-ISIS-CFG], and the routing policy configuration
model is described in [RTG-POLICY-MODEL]. At the time of writing
this document, some work to enhance these two other documents so that
they include configurations related to node administrative tags is
either already in progress or shall be taken up soon.
9. IANA Considerations
This specification updates one IS-IS registry: the "Sub-TLVs for
TLV 242" registry. The following value has been registered.
Value Description
----- -----------
21 Node-Admin-Tag
Sarkar, et al. Standards Track PAGE 8
RFC 7917 Node Administrative Tags in IS-IS July 2016
10. References
10.1. Normative References
[ISO10589] International Organization for Standardization,
"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 Standard 10589, 2002.
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC 2119, March 1997,
<http://www.rfc-editor.org/info/RFC 2119>.
[RFC 4971] Vasseur, JP., Ed., Shen, N., Ed., and R. Aggarwal, Ed.,
"Intermediate System to Intermediate System (IS-IS)
Extensions for Advertising Router Information", RFC 4971,
DOI 10.17487/RFC 4971, July 2007,
<http://www.rfc-editor.org/info/RFC 4971>.
[RFC 5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, DOI 10.17487/RFC 5304,
October 2008, <http://www.rfc-editor.org/info/RFC 5304>.
[RFC 5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, DOI 10.17487/RFC 5310,
February 2009, <http://www.rfc-editor.org/info/RFC 5310>.
10.2. Informative References
[RFC 1997] Chandra, R., Traina, P., and T. Li, "BGP Communities
Attribute", RFC 1997, DOI 10.17487/RFC 1997, August 1996,
<http://www.rfc-editor.org/info/RFC 1997>.
[RFC 5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120,
DOI 10.17487/RFC 5120, February 2008,
<http://www.rfc-editor.org/info/RFC 5120>.
[RFC 5130] Previdi, S., Shand, M., Ed., and C. Martin, "A Policy
Control Mechanism in IS-IS Using Administrative Tags",
RFC 5130, DOI 10.17487/RFC 5130, February 2008,
<http://www.rfc-editor.org/info/RFC 5130>.
Sarkar, et al. Standards Track PAGE 9
RFC 7917 Node Administrative Tags in IS-IS July 2016
[RFC 5286] Atlas, A., Ed., and A. Zinin, Ed., "Basic Specification
for IP Fast Reroute: Loop-Free Alternates", RFC 5286,
DOI 10.17487/RFC 5286, September 2008,
<http://www.rfc-editor.org/info/RFC 5286>.
[RFC 5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC 5305,
October 2008, <http://www.rfc-editor.org/info/RFC 5305>.
[RFC 6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC 6020, October 2010,
<http://www.rfc-editor.org/info/RFC 6020>.
[RFC 7777] Hegde, S., Shakir, R., Smirnov, A., Li, Z., and B.
Decraene, "Advertising Node Administrative Tags in OSPF",
RFC 7777, DOI 10.17487/RFC 7777, March 2016,
<http://www.rfc-editor.org/info/RFC 7777>.
[RFC 7916] 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/RFC 7916,
July 2016, <http://www.rfc-editor.org/info/RFC 7916>.
[RTG-POLICY-MODEL]
Shaikh, A., Shakir, R., D'Souza, K., and C. Chase,
"Routing Policy Configuration Model for Service Provider
Networks", Work in Progress,
draft-ietf-rtgwg-policy-model-01, April 2016.
[YANG-ISIS-CFG]
Litkowski, S., Yeung, D., Lindem, A., Zhang, J., and L.
Lhotka, "YANG Data Model for IS-IS protocol", Work in
Progress, draft-ietf-isis-yang-isis-cfg-08, March 2016.
Sarkar, et al. Standards Track PAGE 10
RFC 7917 Node Administrative Tags in IS-IS July 2016
Acknowledgments
Many thanks to Les Ginsberg, Dhruv Dhody, Uma Chunduri, and Chris
Bowers for providing useful inputs.
Contributors
Many many thanks to Ebben Aries and Rafael Rodriguez for their help
with reviewing and improving the text of this document. Many thanks
to Harish Raguveer for his contributions to initial draft versions of
the document as well. Finally, many thanks to Zhenbin Li for
providing some valuable use cases.
Authors' Addresses
Pushpasis Sarkar (editor)
Individual Contributor
Email: pushpasis.ietf@gmail.com
Hannes Gredler
RtBrick Inc.
Email: hannes@rtbrick.com
Shraddha Hegde
Juniper Networks, Inc.
Electra, Exora Business Park
Bangalore, KA 560103
India
Email: shraddha@juniper.net
Stephane Litkowski
Orange
Email: stephane.litkowski@orange.com
Bruno Decraene
Orange
Email: bruno.decraene@orange.com
Sarkar, et al. Standards Track PAGE 11
RFC TOTAL SIZE: 23344 bytes
PUBLICATION DATE: Tuesday, July 12th, 2016
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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