Internet DRAFT - draft-hegde-ospf-node-admin-tag
draft-hegde-ospf-node-admin-tag
Open Shortest Path First IGP S. Hegde
Internet-Draft H. Raghuveer
Intended status: Standards Track H. Gredler
Expires: December 28, 2014 Juniper Networks, Inc.
R. Shakir
British Telecom
A. Smirnov
Cisco Systems, Inc.
Z. Li
Huawei Technologies
June 26, 2014
Advertising per-node administrative tags in OSPF
draft-hegde-ospf-node-admin-tag-02
Abstract
This document describes an extension to OSPF protocol [RFC2328] to
add an optional operational capability, that allows tagging and
grouping of the nodes in an OSPF domain. This allows
simplification,ease of management and control over route and path
selection based on configured policies.
This document describes the protocol extensions to disseminate per-
node admin-tags to the OSPFv2 and OSPFv3 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
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 December 28, 2014.
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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Administrative Tag TLV . . . . . . . . . . . . . . . . . . . 3
4. OSPF per-node administrative tag TLV . . . . . . . . . . . . 3
4.1. TLV format . . . . . . . . . . . . . . . . . . . . . . . 3
4.2. Elements of procedure . . . . . . . . . . . . . . . . . . 4
5. Applications . . . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
This document provides mechanisms to advertise per-node
administrative tags in the OSPF Router Information LSA [RFC4970]. In
certain path-selection applications like for example in traffic-
engineering or LFA backup 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. Applicability
For the purpose of advertising per-node administrative tags within
OSPF a new TLV is proposed. Because path selection is a functional
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set which applies both to TE and non-TE applications, this new TLV is
carried in the Router Information LSA (RI LSA) [RFC4970]
3. Administrative Tag TLV
An administrative Tag is a 32-bit integer value that can be used to
identify a group of nodes in the OSPF domain.
The new TLV defined will be carried within an RI LSA for OSPFV2 and
OSPFV3. Router information LSA [RFC4970] can have link,area or AS
level flooding scope. Choosing the flooding scope to flood the group
tags are defined by the policies and is a local matter.
The TLV specifies one or more administrative tag values. An OSPF
node advertises the set of groups it is part of in the OSPF domain.
(for example, all PE-nodes are configured with certain tag value, all
P-nodes are configured with a different tag value in a domain). The
total number of admin tags that a given router can advertise at one
time is restricted to 64. If more tags are needed in future, multi-
instancing of the RI LSA [RFC4970] may be required.
4. OSPF per-node administrative tag TLV
4.1. TLV format
The format of the TLVs within the body of an RI LSA is the same as
the format used by the Traffic Engineering Extensions to OSPF
[RFC3630].
The LSA payload consists of one or more nested Type/Length/Value
(TLV) triplets. The format of each TLV is:
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: OSPF per-node Administrative Tag TLV
Type : TBA
Length: A 16-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. The number of tags carried in this TLV is restricted to 64.
4.2. Elements of procedure
Meaning of the Node administrative tags is generally opaque to OSPF.
Router advertising the Node administrative tag (or tags) may be
configured to do so without knowing (or even explicitly supporting)
functionality implied by the tag.
Interpretation of the tag values is implementation-specific. The
meaning of a Node administrative tag is defined by the network local
policy and is controlled via the configuration. There are no tag
values defined by this specification.
The semantics of the tag order has no meaning. That is, 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. Whether or not tag A
precedes or succeeds tag B SHOULD not change the meaning of the tag
set.
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To avoid incomplete or inconsistent interpretations of the Node
administrative tags the same tag value MUST NOT be advertised by a
router in RI LSAs of different scopes. The same tag MAY be
advertised in multiple RI LSAs of the same scope, for example, OSPF
Area Border Router (ABR) may advertise the same tag in area-scope RI
LSAs in multiple areas connected to the ABR.
The Node administrative tags are not meant to be extended by the
future OSPF standards. The new OSPF extensions MUST NOT require use
of Node administrative tags or define well-known tag values.
Instead, the future OSPF extensions must define their own data
signaling tailored to the needs of the feature.
Being part of the RI LSA, the Node administrative tag TLV must be
reasonably small and stable. In particular, but not limited to,
implementations supporting the Node administrative tags MUST NOT tie
advertised tags to changes in the network topology (both within and
outside the OSPF domain) or reachability of routes.
5. Applications
This section lists several examples of how implementations might use
the 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. Service auto-discovery
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. Fast-Rerouting policy
Increased deployment of Loop Free Alternates (LFA) as defined in
[RFC5286] poses operation and management challenges.
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[I-D.litkowski-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.
(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 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) LFA calculation optimization
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.
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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
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 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 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 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 node administrative
tags.
6. Security Considerations
This document does not introduce any further security issues other
than those discussed in [RFC2328] and [RFC5340].
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7. IANA Considerations
IANA maintains the registry for the TLVs. OSPF Administrative Tags
will require one new type code for the TLV defined in this document.
8. Acknowledgments
Thanks to Bharath R and Pushpasis Sarakar for useful inputs. Thanks
to Chris Bowers for providing useful inputs to remove ambiguity
related to tag-ordering.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630, September
2003.
[RFC4970] Lindem, A., Shen, N., Vasseur, JP., Aggarwal, R., and S.
Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 4970, July 2007.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.
9.2. Informative References
[I-D.ietf-rtgwg-remote-lfa]
Bryant, S., Filsfils, C., Previdi, S., Shand, M., and S.
Ning, "Remote LFA FRR", draft-ietf-rtgwg-remote-lfa-02
(work in progress), May 2013.
[I-D.litkowski-rtgwg-lfa-manageability]
Litkowski, S., Decraene, B., Filsfils, C., and K. Raza,
"Operational management of Loop Free Alternates", draft-
litkowski-rtgwg-lfa-manageability-01 (work in progress),
February 2013.
[RFC5286] Atlas, A. and A. Zinin, "Basic Specification for IP Fast
Reroute: Loop-Free Alternates", RFC 5286, September 2008.
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Authors' Addresses
Shraddha Hegde
Juniper Networks, Inc.
Embassy Business Park
Bangalore, KA 560093
India
Email: shraddha@juniper.net
Harish Raghuveer
Juniper Networks, Inc.
Embassy Business Park
Bangalore 560093
India
Email: hraghuveer@juniper.net
Hannes Gredler
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
US
Email: hannes@juniper.net
Rob Shakir
British Telecom
Email: rob.shakir@bt.com
Anton Smirnov
Cisco Systems, Inc.
De Kleetlaan 6a
Diegem 1831
Belgium
Email: as@cisco.com
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Li Zhenbin
Huawei Technologies
Huawei Bld. No.156 Beiqing Rd
Beijing 100095
China
Email: lizhenbin@huawei.com
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