Internet DRAFT - draft-psarkar-isis-node-admin-tag
draft-psarkar-isis-node-admin-tag
IS-IS for IP Internets P. Sarkar, Ed.
Internet-Draft H. Gredler
Intended status: Standards Track S. Hegde
Expires: April 27, 2015 Juniper Networks, Inc.
S. Litkowski
B. Decraene
Orange
Z. Li
Huawei Technologies
H. Raghuveer
October 24, 2014
Advertising Per-node Admin Tags in IS-IS
draft-psarkar-isis-node-admin-tag-03
Abstract
This document describes an extension to IS-IS protocol [ISO10589],
[RFC1195] to add an optional operational capability, that allows
tagging and grouping ofthe nodes in an IS-IS domain. This allows
simple management and easy control over route and path selection,
based on local configured policies.
This document describes the protocol extensions to disseminate per-
node administrative tags in IS-IS protocols.
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 April 27, 2015.
Copyright Notice
Copyright (c) 2014 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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Administrative Tag . . . . . . . . . . . . . . . . . . . . . 2
3. TLV format . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Per-node Admin Tag sub-TLV . . . . . . . . . . . . . . . 4
4. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 5
5. Applications . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
This document provides mechanisms to advertise per-node
administrative tags in the IS-IS Link State PDU [RFC1195]. In
certain path-selection applications like for example in traffic-
engineering or LFA [RFC5286] selection there is a need to tag the
nodes based on their roles in the network and have policies to prefer
or prune a certain group of nodes.
2. Administrative Tag
For the purpose of advertising per-node administrative tags within
IS-IS, a new sub-TLV to the IS-IS Router Capability TLV-242 that is
defined in [RFC4971] is proposed. Because path selection is a
functional set which applies both to TE and non-TE applications the
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same has not been added as a new sub-TLV in the Traffic Engineering
TLVs [RFC5305].
An administrative Tag is a 32-bit integer value that can be used to
identify a group of nodes in the IS-IS domain. The new sub-TLV
specifies one or more administrative tag values. An IS-IS router
advertises the set of groups it is part of in the specific IS-IS
level. As an example, all PE-nodes may be configured with certain
tag value, whereas all P-nodes are configured with a different tag
value in.
The new sub-TLV defined will be carried inside the IS-IS Router
Capability TLV-242 (defined in [RFC4971]) in the Link State PDUs
originated by the router. Link State PDUs [ISO10589] that has either
level-wise (i.e. L1 or L2) or domain-wide flooding scope. Choosing
the flooding scope to flood the group tags are defined by the needs
of the operator's usage and is a matter of local policy or
configuration.
Operator may choose to advertise a set of per-node administrative
tags across levels and another set of per-node administrative tags
within the specific level. But evidently the same set of per-node
administrative tags cannot be advertised both across levels and
within a specific level. A receiving IS-IS router will not be able
to distinguish between the significance of a per-node administrative
tag advertised globally from that of a administrative tag advertised
locally if they have the same value associated but different
significance across different scopes.
Implementations SHOULD allow configuring one or more 'global' as well
as 'level-wide' administrative tags. A operator may only need to
advertise and flood a specific per-node administrative tag, either
across all levels, or only within a specific level. Hence
implementations MUST NOT allow configuring the same per-node
administrative tag values in both 'global' and 'level-wide' scopes.
However the same administrative tag value MAY be allowed to be
configured and advertised for multiple levels with 'level-wide'
flooding scope.
The 'global' per-node administrative tags shall have significance
across the entire administrative domain and hence MUST be advertised
in a Router-Capability TLV with 'global' scope (i.e. S-bit set to
1), and inserted in the LSP PDUs generated for all levels applicable.
The 'level-wide' administrative tags should be copied in to a Router-
Capability with 'level-wide' scope only (i.e S-bit reset to 0) and
copied into the LSP PDU for the specific level.
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In deployments using multi-topology routing [RFC5120], since multiple
topologies within same IS-IS level share the same flooding scope
configuring the same per-node administrative tag across different
topologies, SHOULD NOT be allowed. Advertising the same tag value
across multiple topologies will lead to same inconsistencies as with
the case of advertising same tag value across 'global' and 'level-
wide' flooding scope. If there is need to distinguish between the
per-node administrative tags used for one topology to another,
operators are advised to use disjoint sets of per-node administrative
tags across such topologies.
3. TLV format
3.1. Per-node Admin Tag sub-TLV
The new Per-node Administrative Tag sub-TLV, like other ISIS
Capability sub-TLVs, is formatted as Type/Length/Value (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 : TBA
Length: A 8-bit field that indicates the length of the value
portion in octets and will be a multiple of 4 octets
dependent on the number of tags advertised.
Value: A sequence of multiple 4 octets defining the
administrative tags.
Figure 1: IS-IS Per-node Administrative Tag sub-TLV
The 'Per-node Admin Tag' sub-TLV may be generated more than once by
an originating router. This MAY happen if a node carries more than
63 per-node administrative groups and a single sub-TLV does not
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provide sufficient space. As such occurence of the 'Per-node Admin
Tag' sub-TLV does not cancel previous announcements, but rather is
cumulative.
4. Elements of Procedure
Meaning of the Per-node administrative tags is generally opaque to
IS-IS. Router advertising the per-node administrative tag (or tags)
may be configured to do so without knowing (or even explicitly
supporting) functionality implied by the tag.
Interpretation of tag values is specific to the administrative domain
of a particular network operator. The meaning of a per-node
administrative tag is defined by the network local policy and is
controlled via the 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 [RFC4971].
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 policy to perform a policy action. Tags carried by the
administrative tag TLV SHOULD be used to indicate independent
characteristics of a node. The TLV SHOULD 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).
As mentioned earlier, to avoid incomplete or inconsistent
interpretations of the per-node administrative tags the same tag
value MUST NOT be advertised by a router in Router Capabilities of
different scopes. Implementations MUST NOT allow configuring the
same tag value across domain-wide and 'level-wide' scopes. The same
tag value MAY be allowed to be configured and advertised under
'level-wide' scope for all levels. A IS-IS Area Border Routers (ABR)
participating in both levels 1 and 2 MAY advertise the same tag value
in the level-specific Router Capability TLVs with 'level-wide' scope
(S-bit reset to 0) generated by it. But the same tag value MUST not
be advertised in any of level 1 or level 2 Router-Capability TLV with
'global' scope (S-bit set to 1).
The per-node administrative tags are not meant to be extended by the
future IS-IS standards. The new IS-IS extensions MUST NOT require
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use of per-node administrative tags or define well-known tag values.
Per-node administrative tags are for generic use and do not require
IANA registry. The future IS-IS extensions requiring well known
values MAY use new Capability sub-TLVs tailored to the needs of the
feature, as defined in [RFC4971].
Being part of the Router Capability TLV, the per-node administrative
tag sub-TLV MUST be reasonably small and stable. In particular, but
not limited to, implementations supporting the per-node
administrative tags MUST NOT tie advertised tags to changes in the
network topology (both within and outside the IS-IS domain) or
reachability of routes.
5. Applications
This section lists several examples of how implementations might use
the Per-node administrative tags. These examples are given only to
demonstrate generic usefulness of the router tagging mechanism.
Implementation supporting this specification is not required to
implement any of the use cases. It is also worth noting that in some
described use cases routers configured to advertise tags help other
routers in their calculations but do not themselves implement the
same functionality.
1. Auto-discovery of Services
Router tagging may be used to automatically discover group of
routers sharing a particular service.
For example, service provider might desire to establish full mesh
of MPLS TE tunnels between all PE routers in the area of MPLS VPN
network. Marking all PE routers with a tag and configuring
devices with a policy to create MPLS TE tunnels to all other
devices advertising this tag will automate maintenance of the
full mesh. When new PE router is added to the area, all other PE
devices will open TE tunnels to it without the need of
reconfiguring them.
2. Policy-based Fast-Reroute
Increased deployment of Loop Free Alternates (LFA) as defined in
[RFC5286] poses operation and management challenges.
[I-D.ietf-rtgwg-lfa-manageability] proposes policies which, when
implemented, will ease LFA operation concerns.
One of the proposed refinements is to be able to group the nodes
in IGP domain with administrative tags and engineer the LFA based
on configured policies.
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(a) Administrative limitation of LFA scope
Service provider access infrastructure is frequently designed
in layered approach with each layer of devices serving
different purposes and thus having different hardware
capabilities and configured software features. When LFA
repair paths are being computed, it may be desirable to
exclude devices from being considered as LFA candidates based
on their layer.
For example, if the access infrastructure is divided into the
Access, Distribution and Core layers it may be desirable for
a Distribution device to compute LFA only via Distribution or
Core devices but not via Access devices. This may be due to
features enabled on Access routers; due to capacity
limitations or due to the security requirements. Managing
such a policy via configuration of the router computing LFA
is cumbersome and error prone.
With the Per-node administrative tags it is possible to
assign a tag to each layer and implement LFA policy of
computing LFA repair paths only via neighbors which advertise
the Core or Distribution tag. This requires minimal per-node
configuration and network automatically adapts when new links
or routers are added.
(b) Optimizing LFA calculations
Calculation of LFA paths may require significant resources of
the router. One execution of Dijkstra algorithm is required
for each neighbor eligible to become next hop of repair
paths. Thus a router with a few hundreds of neighbors may
need to execute the algorithm hundreds of times before the
best (or even valid) repair path is found. Manually
excluding from the calculation neighbors which are known to
provide no valid LFA (such as single-connected routers) may
significantly reduce number of Dijkstra algorithm runs.
LFA calculation policy may be configured so that routers
advertising certain tag value are excluded from LFA
calculation even if they are otherwise suitable.
3. Controlling Remote LFA tunnel termination
[I-D.ietf-rtgwg-remote-lfa] proposed method of tunneling traffic
after connected link failure to extend the basic LFA coverage and
algorithm to find tunnel tail-end routers fitting LFA
requirement. In most cases proposed algorithm finds more than
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one candidate tail-end router. In real life network it may be
desirable to exclude some nodes from the list of candidates based
on the local policy. This may be either due to known limitations
of the per-node (the router does accept targeted LDP sessions
required to implement Remote LFA tunneling) or due to
administrative requirements (for example, it may be desirable to
choose tail-end router among co-located devices).
The Per-node administrative tag delivers simple and scalable
solution. Remote LFA can be configured with a policy to accept
during the tail-end router calculation as candidates only routers
advertising certain tag. Tagging routers allows to both exclude
nodes not capable of serving as Remote LFA tunnel tail-ends and
to define a region from which tail-end router must be selected.
4. Mobile backhaul network service deployment
The topology of mobile backhaul network usually adopts ring
topology to save fiber resource and it is divided into the
aggregate network and the access network. Cell Site
Gateways(CSGs) connects the eNodeBs and RNC(Radio Network
Controller) Site Gateways(RSGs)connects the RNCs. The mobile
traffic is transported from CSGs to RSGs. The network takes a
typical aggregate traffic model that more than one access rings
will attach to one pair of aggregate site gateways(ASGs) and more
than one aggregate rings will attach to one pair of RSGs.
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----------------
/ \
/ \
/ \
+------+ +----+ Access +----+
|eNodeB|---|CSG1| Ring 1 |ASG1|-------------
+------+ +----+ +----+ \
\ / \
\ / +----+ +---+
\ +----+ |RSG1|----|RNC|
-------------| | Aggregate +----+ +---+
|ASG2| Ring |
-------------| | +----+ +---+
/ +----+ |RSG2|----|RNC|
/ \ +----+ +---+
/ \ /
+------+ +----+ Access +----+ /
|eNodeB|---|CSG2| Ring 2 |ASG3|------------
+------+ +----+ +----+
\ /
\ /
\ /
-----------------
Figure 2: Mobile Backhaul Network
A typical mobile backhaul network with access rings and aggregate
links is shown in figure above. The mobile backhaul networks
deploy traffic engineering due to the strict Service Level
Agreements(SLA). The TE paths may have additional constraints to
avoid passing via different access rings or to get completely
disjoint backup TE paths. The mobile backhaul networks towards
the access side change frequently due to the growing mobile
traffic and addition of new eNodeBs. It's complex to satisfy the
requirements using cost, link color or explicit path
configurations. The per-node administrative tag defined in this
document can be effectively used to solve the problem for mobile
backhaul networks. The nodes in different rings can be assigned
with specific tags. TE path computation can be enhanced to
consider additional constraints based on per-node administrative
tags.
5. Policy-based Explicit Routing
Partially meshed network provides multiple paths between any two
nodes in the network. In a data center environment, the topology
is usually highly symmetric with many/all paths having equal
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cost. In a long distance network, this is usually less the case
for a variety of reasons (e.g. historic, fiber availability
constraints, different distances between transit nodes, different
roles ...). Hence between a given source and destination, a path
is typically preferred over the others, while between the same
source and another destination, a different path may be
preferred.
+--------------------+
| |
| +----------+ |
| | | |
T-10-T | |
/| /| | |
/ | / | | |
--+ | | | | |
/ +--+-+ 100 | |
/ / | | | |
/ / R-18-R | |
/ / /\ /\ | |
/ | / \ / \ | |
/ | / x \ | |
A-25-A 10 10 \ \ | |
/ / 10 10 | |
/ / \ \ | |
A-25-A A-25-A | |
\ \ / / | |
201 201 201 201 | |
\ \ / / | |
\ x / | |
\ / \ / | |
\/ \/ | |
I-24-I 100 100
| | | |
| +-----------+ |
| |
+---------------------+
Figure 3: Explicit Routing topology
In the above topology, operator may want to enforce the following
high level explicitly routed policies: - Traffic from A nodes to
A nodes must not go through I nodes - Traffic from A nodes to I
nodes must not go through R and T nodes with per-node
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administrative tag, tag A can be configured on all A nodes,
(similarly I, R, T), and then configure this single CSPF policy
on all A nodes to avoid I nodes for path calculation.
6. Security Considerations
This document does not introduce any further security issues other
than those discussed in [ISO10589] and [RFC1195].
7. IANA Considerations
IANA maintains the registry for the Router Capability sub-TLVs. IS-
IS Administrative Tags will require new type code for the following
new sub-TLV defined in this document.
i) Per-Node-Admin-Tag Sub-TLV, Type: TBD
8. Acknowledgments
Many thanks to Les Ginsberg, Dhruv Dhody, Uma Chunduri for useful
inputs. Thanks to Chris Bowers for providing useful inputs to remove
ambiguity related to tag-ordering.
9. References
9.1. 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.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
9.2. Informative References
[I-D.ietf-rtgwg-lfa-manageability]
Litkowski, S., Decraene, B., Filsfils, C., Raza, K.,
Horneffer, M., and p. psarkar@juniper.net, "Operational
management of Loop Free Alternates", draft-ietf-rtgwg-lfa-
manageability-04 (work in progress), August 2014.
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[I-D.ietf-rtgwg-remote-lfa]
Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N.
So, "Remote LFA FRR", draft-ietf-rtgwg-remote-lfa-08 (work
in progress), September 2014.
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.
[RFC4971] Vasseur, JP., Shen, N., and R. Aggarwal, "Intermediate
System to Intermediate System (IS-IS) Extensions for
Advertising Router Information", RFC 4971, July 2007.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120, February 2008.
[RFC5286] Atlas, A. and A. Zinin, "Basic Specification for IP Fast
Reroute: Loop-Free Alternates", RFC 5286, September 2008.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, October 2008.
Authors' Addresses
Pushpasis Sarkar (editor)
Juniper Networks, Inc.
Electra, Exora Business Park
Bangalore, KA 560103
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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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
Li Zhenbin
Huawei Technologies
Huawei Bld. No.156 Beiqing Rd
Beijing, KA 100095
China
Email: lizhenbin@huawei.com
Harish Raghuveer
Email: harish.r.prabhu@gmail.com
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