Open Shortest Path First IGP S. Hegde
Internet-Draft Juniper Networks, Inc.
Intended status: Standards Track H. Raghuveer
Expires: September 10, 2015
H. Gredler
Juniper Networks, Inc.
R. Shakir
British Telecom
A. Smirnov
Cisco Systems, Inc.
Z. Li
Huawei Technologies
B. Decraene
Orange
March 9, 2015
Advertising per-node administrative tags in OSPF
draft-ietf-ospf-node-admin-tag-01
Abstract
This document describes a mechanism to advertise per-node
administrative tags in 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 administrative-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/.
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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.
Copyright Notice
Copyright (c) 2015 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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Administrative Tag TLV . . . . . . . . . . . . . . . . . . . . 4
3. OSPF per-node administrative tag TLV . . . . . . . . . . . . . 4
3.1. TLV format . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Elements of procedure . . . . . . . . . . . . . . . . . . 5
4. Applications . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
It is useful to assign a per-node administrative tag to a router in
the OSPF domain and use it as an attribute associated with the node.
The per-node administrative tag can be used in traffic-engineering
applications to provide different path-selection criteria. It can
also be used to prefer or prune certain paths in Loop Free Alternate
(LFA) backup selection via local policies.
This document provides mechanisms to advertise per-node
administrative tags in the OSPF. Path selection is a functional set
which applies both to TE and non-TE applications. A new TLV is
defined for carrying per-node administrative tags and is included in
Router Information LSA [RFC4970] .
2. 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).
Multiple TLVs MAY be added in same RI-LSA or in different instance of
the RI LSA as defined in [I-D.acee-ospf-rfc4970bis].
3. OSPF per-node administrative tag TLV
3.1. TLV format
As per [RFC4970], 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. Atleast one tag MUST be carried if this TLV is included in the
RI-LSA.
3.2. Elements of procedure
Meaning of the Node administrative tags is generally opaque to OSPF.
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
RI LSA without any change as defined in [RFC4970].
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
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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 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).
To avoid incomplete or inconsistent interpretations of the per-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 per-node administrative tags are not meant to be extended by the
future OSPF standards. The new OSPF extensions MUST NOT require use
of per-node administrative tags or define well-known tag values.
Node administrative tags are for generic use and do not require IANA
registry. The future OSPF extensions requiring well known values MAY
define their own data signaling tailored to the needs of the feature
or MAY use capability TLV as defined in [RFC4970].
Being part of the RI LSA, the per-node administrative tag 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 OSPF domain) or reachability of routes.
4. 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
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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.
[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.
(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.
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(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.
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 not 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
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than one aggregate rings will attach to one pair of RSGs.
----------------
/ \
/ \
/ \
+------+ +----+ 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.
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5. Explicit routing policy
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
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
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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 node admin 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.
5. Security Considerations
This document does not introduce any further security issues other
than those discussed in [RFC2328] and [RFC5340].
6. IANA Considerations
This specification updates one OSPF registry: OSPF Router Information
(RI) TLVs Registry
i) TBD - Node Admin tag TLV
7. Acknowledgments
Thanks to Bharath R, Pushpasis Sarakar and Dhruv Dhody for useful
inputs. Thanks to Chris Bowers for providing useful inputs to remove
ambiguity related to tag-ordering. Thanks to Les Ginsberg and Acee
Lindem for the inputs.
8. References
8.1. 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.
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[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.
8.2. Informative References
[I-D.acee-ospf-rfc4970bis]
Lindem, A., Shen, N., Vasseur, J., Aggarwal, R., and S.
Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", draft-acee-ospf-rfc4970bis-00 (work
in progress), July 2014.
[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.
[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.
[RFC5286] Atlas, A. and A. Zinin, "Basic Specification for IP Fast
Reroute: Loop-Free Alternates", RFC 5286, September 2008.
Authors' Addresses
Shraddha Hegde
Juniper Networks, Inc.
Embassy Business Park
Bangalore, KA 560093
India
Email: shraddha@juniper.net
Harish Raghuveer
Email: harish.r.prabhu@gmail.com
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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
Li zhenbin
Huawei Technologies
Huawei Bld. No.156 Beiqing Rd
Beijing, 100095
China
Email: lizhenbin@huawei.com
Bruno Decraene
Orange
Email: bruno.decraene@orange.com
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