Network Working Group P. Srisuresh
INTERNET-DRAFT Kuokoa Networks
Expires as of March 16, 2003 P. Joseph
Force10 Networks
September 16, 2002
TE LSAs to extend OSPF for Traffic Engineering
<draft-srisuresh-ospf-te-03.txt>
Status of this Memo
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Abstract
OSPF is a link state routing protocol used for IP-network
topology discovery and collection and dissemination of link
access metrics. The resulting Link State Database (LSDB) is
used to compute IP address forwarding table based on
shortest-path criteria. Traffic Engineering extensions(OSPF-TE)
outlined in this document are built on the native OSPF
foundation, utilizing new LSAs, designed specifically for TE.
OSPF-TE sets out to discover TE network topology and perform
collection and dissemination of TE metrics within the TE network.
This results in the generation of an independent TE-LSDB, that
would permit computation of TE circuit paths. Unlike the native
OSPF link metrics, TE metrics can be rapidly changing and
varied across different elements of the network. TE circuit
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paths are computed using varied TE criteria, often different
from the shortest-path, to route traffic around congestion
paths. Principal motivations to designing the OSPF-TE over
[OPQLSA-TE] and transition path for vendors currently using
[OPQLSA-TE] to adapt the OSPF-TE are outlined in separate
sections within the document. OSPF-TE provides a single unified
mechanism for traffic engineering across packet and non-packet
networks, and may be adapted for a peer networking model.
Table of Contents
1. Introduction ................................................3
2. Traffic Engineering .........................................4
3. Terminology .................................................5
3.1. OSPF-TE node ...........................................5
3.2. Native OSPF node .......................................5
3.3. TE nodes vs. native(non-TE) nodes ......................6
3.4. TE links vs. native(non-TE) links ......................6
3.5. Packet-TE network vs. non-packet-TE network ............6
3.6. TE topology vs. non-TE topology ........................6
3.7. TLV ....................................................7
3.8. Router-TE TLVs .........................................7
3.9. Link-TE TLVs ...........................................7
4. Motivations to designing the OSPF-TE using TE-LSAs ..........7
4.1. Clean design - TE-LSDB, independent of the native LSDB .7
4.2. Extendible design - based on the OSPF foundation .......8
4.3. Scalable design - TE-AS may be sub-divided into areas ..9
4.4. Unified design - for packet and non-packet networks ....9
4.5. Efficient design - in LSA content and flooding reach ..10
4.6. SLA enforceable TE network can coexist with IP network 10
4.7. Right Framework for future OSPF extensibility .........11
4.8. Network scenarios benefiting from the OSPF-TE design ..12
4.8.1. IP providers transitioning to TE services ......12
4.8.2. Providers offering Best-effort IP & TE services.12
4.8.3. Multi-area networks ............................12
4.8.4. Non-packet and Peer-networking models ..........12
5. OSPF-TE solution, assumptions and limitations ..............13
5.1. OSPF-TE Solution ......................................14
5.2. Assumptions ...........................................16
5.3. Limitations ...........................................16
6. Transition strategy for implementations using Opaque LSAs ..16
7. The OSPF Options field .....................................16
8. Bringing up TE adjacencies; TE vs. Non-TE topologies .......17
8.1. The Hello Protocol ....................................17
8.2. Flooding and the Synchronization of Databases .........18
8.3. The Designated Router .................................19
8.4. The Backup Designated Router ..........................19
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8.5. The graph of adjacencies ..............................19
9. TE LSAs ....................................................20
9.1. TE-Router LSA (0x81) ..................................22
9.1.1. Router-TE flags - TE capabilities of the router.24
9.1.2. Router-TE TLVs .................................25
9.1.3. Link-TE options - TE capabilities of a TE-link .26
9.1.4. Link-TE TLVs ...................................26
9.2. TE-incremental-link-Update LSA (0x8d) .................27
9.3. TE-Circuit-paths LSA (0x8C) ...........................29
9.4. TE-Summary LSAs .......................................31
9.4.1. TE-Summary Network LSA (0x83) ..................31
9.4.2. TE-Summary router LSA (0x84) ...................32
9.5. TE-AS-external LSAs (0x85) ............................34
9.6. Changes to Network LSA ................................35
9.6.1. Positional-Ring type network LSA ...............36
9.7. TE-Router-Proxy LSA (0x8e) ............................36
9.8. Others ................................................37
10. Abstract topology representation with TE support ...........37
11. Changes to Data structures in OSPF-TE routers ..............39
11.1. Changes to Router data structure .....................39
11.2. Two set of Neighbors .................................39
11.3. Changes to Interface data structure ..................39
12. IANA Considerations ........................................40
12.1. TE-compliant-SPF routers Multicast address allocation 40
12.2. New TE-LSA Types .....................................40
12.3. New TLVs (Router-TE and Link-TE TLVs) ................40
12.3.1. TE-selection-Criteria TLV (Tag ID = 1) .......40
12.3.2. MPLS-Signaling protocol TLV (Tag ID = 3) .....40
12.3.3. Constraint-SPF algorithms-Support TLV (Tag ID=4)
12.3.4. SRLG-TLV (Tag ID = 0x81) .....................40
12.3.5. BW-TLV (Tag ID = 0x82) .......................41
12.3.6. CO-TLV (Tag ID = ox83) .......................41
13. Acknowledgements ...........................................41
14. Security Considerations ....................................41
References .....................................................41
1. Introduction
There is substantial industry experience with deploying OSPF link
state routing protocol. That makes OSPF a good candidate to adapt
for traffic engineering purposes. The dynamic discovery of network
topology, link access metrics, flooding algorithm and the
hierarchical organization of areas can all be used effectively in
creating and tearing traffic links on demand. The intent of
OSPF-TE is to discover TE network topology and the TE metrics
of the nodes and links in the network.
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The objective of traffic engineering is to set up circuit path(s)
across a pair of nodes or links, as the case may be, so as to
forward traffic of a certain forwarding equivalency class. Circuit
emulation in a packet network is accomplished by each MPLS
intermediary node performing label swapping. Whereas, circuit
emulation in a TDM or Fiber cross-connect network is accomplished
by configuring the switch fabric in each intermediary node to do
the appropriate switching (TDM, fiber or Lamda) for the duration
of the circuit.
The objective of this document is not how to set up traffic circuits,
but rather provide the necessary TE parameters for the nodes and
links that constitute the TE topology. Unlike the native OSPF,
OSPF-TE will be used to build circuit paths, meeting certain TE
criteria. The only requirement is that end-nodes and/or end-links of
a circuit be identifiable with an IP address.
The approach suggested in this document is different from the
Opaque-LSA-based approach outlined in [OPQLSA-TE]. Section 4
describes the motivations behind designing OSPF-TE. Section 6
outlines a strategy to transition Opaque-LSA based implementations
to adapt the OSPF-TE outlined here.
2. Traffic engineering overview
A traffic engineered circuit may be identified by the tuple of
(Forwarding Equivalency Class, TE parameters for the circuit,
Origin Node/Link, Destination node/Link).
The Forwarding Equivalency Class(FEC) may be constituted of a number
of criteria such as (a) Traffic arriving on a specific interface,
(b) Traffic meeting a certain classification criteria (ex: based on
fields in the IP and transport headers), (c) Traffic in a certain
priority class, (d) Traffic arriving on a specific set of TDM (STS)
circuits on an interface, (e) Traffic arriving on a certain
wave-length of an interface, (f) Traffic arriving at a certain time
of day, and so on. A FEC may be constituted as a combination of one
or more of the above criteria. Discerning traffic based on the FEC
criteria is a mandatory requirement on Label Edge Routers (LERs).
Traffic content is transparent to the Intermediate Label Switched
Routers (LSRs), once a circuit is formed. LSRs are simply
responsible for keeping the circuit in-tact for the lifetime of the
circuit(s). As such, this document will not address FEC or the
associated signaling to setup circuits. [MPLS-TE] and [GMPLS-TE]
address the FEC criteria. Whereas, [RSVP-TE] and [CR-LDP] address
different types of signaling protocols.
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This document is concerned with the collection of TE parameters for
all the nodes and links within an autonomous system. TE parameters
for a node may include a) ability to perform traffic prioritization,
b) ability to provision bandwidth on interfaces, c) support for zero
or more CSPF algorithms, d) support for a specific TE-Circuit switch
type, e) support for a certain type of automatic protection
switching and so forth. TE parameters for a link may include
a) available bandwidth, b) reliability of the link, c) color
assigned to the link, d) cost of bandwidth usage on the link, and
e) membership to a Shared Risk Link Group (SRLG) and so forth.
Only the unicast paths circuit paths are considered here. Multicast
variations are currently considered out of scope for this document.
The requirement is that the originating as well as the terminating
entities of a TE path are identifiable by their IP address.
3. Terminology
Definitions for majority of the terms used in this document with
regard to OSPF protocol may be found in [OSPF-V2]. MPLS and traffic
engineering terms may be found in [MPLS-ARCH]. RSVP-TE and CR-LDP
signaling specific terms may be found in [RSVP-TE] and [CR-LDP]
respectively.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALLNOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC 2119.
Below are definitions for the terms used within this document.
3.1. OSPF-TE node
This is a router that supports the OSPF-TE described in this
document. At least one of the attached links for the node
supports IP packet termination and runs the OSPF-TE protocol.
An OSPF-TE node supports native OSPF as well as the OSPF-TE.
3.2. Native OSPF node
A native OSPF node is an OSPF router that does not support
the TE extensions described in this document or does not have
a TE link attached to it. A Native OSPF node forwards IP
traffic, using the shortest-path forwarding algorithm.
A native OSPF node may be enhanced to be an OSPF-TE node. An
autonomous system (AS) could be constituted of a combination
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of native-OSPF and OSPF-TE nodes.
3.3. TE nodes vs. native(non-TE) nodes
A TE-Node is an intermediate or edge node taking part in the
traffic engineered (TE) network. A TE-circuit is constituted of
a series of TE nodes connected to each other through TE links.
In a SONET/TDM network or a photonic cross-connect network,
a TE node is not required to support OSPF-TE. An external
OSPF-TE node may represent the TE node for protocol processing.
A native (or non-TE) node is an IP router capable of IP packet
forwarding, does not have TE link attachments and does not take
part in a TE network.
3.4. TE links vs. native(non-TE) links
A TE Link is a network attachment that supports traffic
engineering. A TE-circuit is constituted of a series of TE
nodes connected to each other through TE links.
A native (or non-TE) link is one that is used for IP packet
traversal. A link may be configured to be pure TE link or
native link or a both.
3.5. Packet-TE network vs. non-packet-TE network
Packet-TE network is one in which TE-circuit emulation is
accomplished by each MPLS intermediary node performing label
swapping on the packet data.
Non-packet-TE network, such as SONET/TDM or Fiber
cross-connect network is one in which TE-circuit emulation is
accomplished by configuring the switch fabric in each
intermediary node to do the appropriate switching (TDM, fiber
or Lamda) for the duration of the circuit.
In either case, OSPF-TE can only be enabled on interfaces
supporting IP packet termination. Interfaces supporting OSPF
and/or OSPF-TE constitute the OSPF control network. The OSPF
control network can be independent of the packet or non-packet
data network.
3.6. TE topology vs. non-TE topology
A TE topology is constituted of a set of contiguous TE nodes and
TE links. Associated with each TE node and link is a set of TE
criteria that may be supported at any given time. A TE topology
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allows circuits to be overlayed statically or dynamically based
on a specific TE criteria.
A non-TE topology specifically refers to the network that does not
support TE. Control protocols such as OSPF may be run on the non-TE
topology. IP forwarding table used to forward IP packets on this
network is built based on the control protocol specific algorithm,
such as OSPF shortest-path criteria.
3.7. TLV
A TLV stands for an object in the form of Tag-Length-Value. All TLVs
are assumed to be of the following format, unless specified
otherwise. The Tag and length are 16 bits wide each. The length
includes the 4 bytes required for Tag and Length specification.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag | Length (4 or more) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3.8. Router-TE TLVs
TLVs used to describe the TE capabilities of a TE-node.
3.9. Link-TE TLVs
TLVs used to describe the TE capabilities of a TE-link.
4. Motivations to designing the OSPF-TE using TE-LSAs
The motivation behind designing the OSPF-TE using TE-LSAs is
that the approach is clean, extendible, scalable, unified,
efficient, and SLA enforceable. The approach also provides
the right framework for future OSPF extensibility. Each of
these motivations is explained in detail in the following
subsections.
The last subsection lists network scenarios that benefit from
the TE-LSA design.
4.1. Clean design - TE-LSDB, independent of the native LSDB
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OSPF-TE using TE LSAs provides a clean separation of Link State
Data Bases (LSDB) between native (SPF-based) and TE networks.
The OSPF-TE dynamically discovers TE network topology and the
associated TE metrics of the nodes and links in the TE network.
OSPF-TE design is based on the tried and tested OSPF paradigm.
As such, it inherits all the benefits of the OSPF, present and
future.
With OSPF-TE, native OSPF nodes will keep just the native OSPF
link state database. The OSPF-TE nodes will keep the native as
well as the TE LSDB. In the case, where the network is used
only for Traffic engineering purposes, the native-LSDB
describes the control topology.
In the Opaque-LSA-based TE scheme([OPQLSA-TE]), the TE-LSDB built
using opaque LSAs refers the native LSDB to build the TE topology.
Further, the LSDB has no knowledge of the TE capabilities of the
routers. Point-to-point links are the only type of links that can
form a TE network. It is apparent that [OPQLSA-TE] is a new
protocol in itself within the constraints of an Opaque-LSA and is
not tailored to benefit from the tried and tested native-OSPF.
4.2. Extendible design - based on the OSPF foundation
TE LSAs are extendible, just as the native OSPF on which OSPF-TE
is founded. [OPQLSA-TE], on the other hand, is not extendible
and is constrained by the Opaque LSA on which it is founded.
For example, Opaque LSAs are not suited to advertising summary
LSAs along a restricted flooding scope (as with TE-Summary
network LSA). Opaque LSAs are also not suited to advertising
incremental TLV changes. A change in any TLV of a TE-link will
mandate the entire Opaque-LSA (with all the TLVs included) to be
transmitted. TE-incremental-link-update LSA, on the other hand,
is capable of advertising just the delta TLVs. Opaque LSAs
are also not extendible to support advertisement of TLVs for
non-members of the OSPF control network. This is a necessity
for certain non-packet networks such as a SONET/TDM network. In
a SONET/TDM network, data-path topology often differs from
its OSPF control network counterpart. TE-Router-Proxy-LSA
(section 9.7) permits advertising LSAs for non-members via
a proxy node that is a member of the control network.
Lastly, the expressibility of data in an Opaque LSA is strictly
restricted to being in the form of TLVs and sub-TLVs, some
mandatorily required and some positionally dependent in the
TLV sequence for interpretation.
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4.3. Scalable design - TE-AS may be sub-divided into areas
OSPF-TE using TE LSAs inherits the hierarchical area organization
used within native-OSPF. Without revealing the nodes and
characteristics of the attached links within a TE-area, the
TE-Summary network LSA (refer section 9.4) advertises the
reachability of TE networks within an area to the areas outside
in the same AS.
Providing area level abstraction and having the abstraction be
distinct for TE and native topologies is a necessity for
inter-area communication. When the topologies are separate, the
area border routers can advertise different summary LSAs to TE
and non-TE routers. For example, a native Area Border router (ABR)
simply announces the shortest path network summary LSAs (LSA
type 3) for nodes outside the area. A TE-ABR, on the other hand,
would use TE-summary network LSA to advertise network Reachability
information - not aggregated path metric as required for a native
OSPF LSDB. Clearly, the data content and flooding scope should be
different for the TE nodes. The flooding boundary for TE-summary
LSAs would be (AS - OriginatingArea - StubAreas - NSSAs).
Opaque-LSA-based TE scheme([OPQLSA-TE]) is restricted for use
within an area and is not applicable for flooding across areas.
As-wide scope Opaque LSAs (Type 11 LSAs) will be unable to restrict
flooding in its own originating area.
4.4. Unified design - for packet and non-packet networks
OSPF-TE uses the same set of TE LSAs for disseminating TE
characteristics - irrespective of whether the network is a packet
network or a non-packet network or a combination of both. Only
the TLVs used to describe the characteristics will vary. Each TE
node will be required to advertise its own TE capabilities and
that of the attached TE links.
In a peer networking TE model, the TE nodes are heterogeneous
and have different TE characteristics. As such, the signaling
protocols will need the TE characteristics of all nodes and
attached links so they can signal the nodes to formulate TE
circuits across heterogeneous nodes. The underlying control
protocol must be capable of providing a unified LSDB for all
nodes in the network. OSPF-TE clearly meets this requirement.
Opaque-LSA-based TE scheme([OPQLSA-TE]) is limited in scope for
packet networks. Extensions ([OPQLSA-GMPLS]) are underway to
support GMPLS links within opaque LSAs. However, neither
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[OPQLSA-TE] nor [OPQLSA-GMPLS] is sufficient by itself or when
combined for use within a peer networking model with heterogeneous
nodes. Neither of the Opaque LSA based extensions have provision
to distinguish between the various nodes and link attachments that
are different from point-to-point connections. SONET specific
ring topologies and packet network specific LAN and other mesh
topologies are not permitted.
4.5. Efficient design - in LSA content and flooding reach
OSPF-TE is capable of identifying the boundaries of a TE topology
and limits the flooding of TE LSAs to only the TE-nodes. Nodes
that do not have TE link attachments are not bombarded with TE
specific LSAs. This is a useful characteristic for networks
supporting native and TE traffic in the same connected network.
The more frequent and wider the flooding scope, the larger the
number of retransmissions and acknowledgements. The same
information (needed or not) may reach a router through multiple
links. Even if the router did not forward the information past
the node, it would still have to send acknowledgements across
all the various links on which the LSAs tried to converge.
Clearly, it is not desirable to flood LSAs to nodes that do not
require it. This can be a considerable impediment to non-TE
nodes in a network that is constituted of native and TE nodes.
Opaque-LSA-based TE scheme([OPQLSA-TE]) makes no distinction
between TE and native OSPF nodes as far as LSA flooding is
concerned. It is possible for the native OSPF nodes to silently
ignore the unsupported Opaque LSAs or add knobs within
implementation to decide whether or not a certain opaque LSA
mandates dijkstra SPF recomputation. In any case, unintended
LSAs are disruptive and can be the cause of a large number of
acknowledgements and retransmissions.
TE metrics in a network could be rapidly changing. Only a subset
of the metrics may be prone to rapid change, while others remain
largely unchanged. Changes must be communicated at the earliest
throughout the network to ensure that the TE-LSDB is up-to-date.
TE-Incremental-Link-update LSA (section 9.2) permits advertising
only a subset of the link metrics and not the entire router-LSA
all over. [OPQLSA-TE] does not have provision to advertise just
the TLVs that changed. A change in any TLV of a TE-link will
mandate the entire LSA to be transmitted. This is clearly a
serious shortcoming in the protocol.
4.6. SLA enforceable TE network can coexist with IP network
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OSPF-TE is designed to draw distinction between links that
support TE traffic and links that support native best-effort
IP traffic. This flexibility to configure links as appropriate
for a service, permits enforceability of service level
agreements (SLAs). A link, configured to support TE traffic
alone will not permit native IP traffic on the link.
Best-effort IP transit network and constraint based TE network
have different SLA requirements and hence different billing
models. Keeping the two networks physically isolated will enable
SLA enforceability, but can be expensive. Combining the two
networks into a single physically connected network will bring
economies of scale, if the SLA enforceability can be retained.
When the links of a TE-network LSDB do not overlap the links
of a native LSDB, such a virtual isolation of networks and
hence SLA enforceability becomes possible.
Opaque-LSA-based TE scheme([OPQLSA-TE]) is inherently not capable
of having two virtual networks in a single physically connected
network. All point-to-point links in a packet network are subject
to best-effort IP traffic, irrespective of whether a link is
usable for TE traffic or not. In order to ensure that TE links are
not cannibalized by best-effort traffic, the network provider will
simply have to restrict best-effort traffic from entering the
network. This is a severe limitation and is a direct result of
not having LSDB isolation. When TE and native topologies
are not separated (as is the case with Opaque-LSAs), a native OSPF
node could be utilizing a TE link as its least cost link, thereby
stressing the TE link and rendering the TE link ineffective for
TE purposes.
4.7. Right Framework for future OSPF extensibility
OSPF-TE design provides the right framework for future OSPF
extensions based on independent service provider needs. The
framework essentially calls for building independent service
specific LSDBs. Each such LSDB will consist of service specific
metrics of all resources within the service-specific topology.
The TE-LSDB permits TLV scalability as well as the ability
to perform fast searches through the database. Just as the
TE-LSDB may be used for MPLS TE application, a different type
of LSDB may be used for a different type of application across
the same physically connected IP network. E.g., one can derive
QOS based IP forwarding on an IP network.
Limiting flooding scope of service specific LSAs within the
service specific topology eliminates LSA contamination between
virtual service networks of a single physically connected
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network. Using service specific LSAs provides flexibility in
LSA content and flooding scope.
Opaque-LSA-based TE scheme([OPQLSA-TE]) works best when a single
type of service is assumed for a single physically connected
network. As such, multiple disparate networks can function
running various flavors of OSPF. [OSPF-v2] for native best-effort
IP networks, [OPQLSA-TE] for packet networks and [OPQLSA-GMPLS]
for non-packet networks.
4.8. Network scenarios benefiting from the OSPF-TE design
Many real-world scenarios are better served by the new-TE-LSAs
scheme. Here are a few examples.
4.8.1. IP providers transitioning to TE services
Providers needing to support MPLS based TE in their IP network
may choose to transition gradually. Perhaps, add new TE links
or convert existing links into TE links within an area first
and progressively advance to offer in the entire AS.
Not all routers will support TE extensions at the same time
during the migration process. Use of TE specific LSAs and their
flooding to OSPF-TE only nodes will allow the vendor to
introduce MPLS TE without destabilizing the existing network.
As such, the native OSPF-LSDB will remain undisturbed while
newer TE links are added to network.
4.8.2. Providers offering Best-effort-IP & TE services
Providers choosing to offer both best-effort-IP and TE based
packet services simultaneously on the same physically connected
network will benefit from the OSPF-TE design. By maintaining
independent LSDBs for each type of service, TE links are not
cannibalized by the non-TE routers for SPF forwarding. Unlike
the [OPQLSA-TE] scheme, OSPF-TE provides the framework for SLA
enforcement.
4.8.3. Multi-area networks
The OSPF-TE design parallels the tried and tested native-OSPF
design. Unlike [OPQLSA-TE], OSPF-TE scales naturally to multi-area
networks.
4.8.4. Non-packet and Peer-networking models
OSPF-TE is the only scheme that can support the following
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network attachments For a non-Packet TE network.
(a) "Positional-Ring" type network LSA and
(b) Router Proxying - allowing a router to advertise on behalf
of other nodes (that are not Packet/OSPF capable).
Opaque LSA based extensions ([OPQLSA-TE], [OPQLSA-GMPLS]) are not
suited to distinguish the heterogeneous nodes in a peer-connected
network. Opaque-LSA based extensions are also not suited to support
link attachments that are different from point-to-point connections.
5. OSPF-TE solution, assumptions and limitations
5.1. OSPF-TE Solution
The OSPF-TE uses the options flag as a means to determine the
TE topology. New TE LSAs are designed to generate an independent
TE-service tailored LSDB. Sections 8.0 and 9.0 describe the TE
extensions in detail. Changes required of the OSPF data
structures in order to support OSPF-TE are described in section
11.0. The OSPF-TE design is based on the tried and tested OSPF
paradigm. With TE-LSDB, you have the advantages of retaining the
scalability of TLV's and the ability to run fast searches through
the database.
With the new TE-LSA scheme, an OSPF-TE node will have two types
of Link state databases (LSDB). A native LSDB that describes the
native control topology and a TE-LSDB that describes the TE
topology. Shortest-Path-First algorithm will be used to forward
IP packets along the native control network. OSPF neighbors data
structure will be used for flooding along the control topology.
The TE-LSDB is constituted only of TE nodes and TE links. A variety
of CSPF algorithms may be used to dynamically setup TE circuit
paths along the TE network. A new TE-neighbors data structure will
be used to flood TE LSAs along the TE-only topology. Clearly, the
the TE nodes will need the control (non-TE) network for OSPF
communication. The control network may also be used for pinging
OSPF-TE nodes and performing any debug and monitoring tasks on
the nodes. However, the ability to make distinction between
TE and non-TE topologies, allows the bandwidth on TE links to be
strictly SLA enforceable, even as a TE link is packet-capable.
The actual characteristics of the TE-link are irrelevant from the
OPSF-TE perspective. As such, that allows for packet and non-packet
networks to operate in peer mode.
Consider the following network where some of the routers and links
are TE enabled and others are native OSPF routers and links. All
nodes in the network belong to the same OSPF area.
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+---+
| |--------------------------------------+
|RT6|\\ |
+---+ \\ |
|| \\ |
|| \\ |
|| \\ |
|| +---+ |
|| | |----------------+ |
|| |RT1|\\ | |
|| +---+ \\ | |
|| //| \\ | |
|| // | \\ | |
|| // | \\ | |
+---+ // | \\ +---+ |
|RT2|// | \\|RT3|------+
| |----------|----------------| |
+---+ | +---+
| |
| |
| |
+---+ +---+
|RT5|--------------|RT4|
+---+ +---+
Legend:
-- Native(non-TE) network link
| Native(non-TE) network link
\\ TE network link
|| TE network link
Figure 6: A (TE + native) OSPF network topology
In the above network, TE and native OSPF Link State Data bases
(LSDB) would have been synchronized within the area along the
following nodes.
Native OSPF LSDB nodes TE-LSDB nodes
---------------------- -------------
RT1, RT2, RT3. RT4, RT5, RT6 RT1, RT2, RT3, RT6
Nodes such as RT1 will have two LSDBs, a native LSDB and a TE-LSDB
to reach native and TE networks. The TE LSA updates will not impact
non-TE nodes RT4 and RT5.
5.2. Assumptions
OSPF-TE design makes the following assumptions.
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1. An OSPF-TE node with links in an OSPF area will need to
establish router adjacency with at least one other neighboring
OSPF-TE node in order for the router's database to be
synchronized with other routers in the area. Failing this, the
OSPF router will not be in the TE calculations of other TE
routers in the area. Refer [FLOOD-OPT] for flooding
optimizations.
2. Unlike the native OSPF, OSPF-TE must be capable of advertising
link state of interfaces that are not capable of handling IP
packet data. As such, the OSPF-TE protocol cannot be required
to synchronize its link-state database with neighbors across
all its links. It is sufficient to synchronize link-state
database in an area, across a subset of the IP termination
links. Yet, the TE LSDB (LSA database) should be synchronized
across all OSPF-TE nodes within an area.
All nodes and interfaces described by the TE LSAs will be
present in the TE topology database (a.k.a. TE LSDB).
3. A link in a packet network can be a TE-link or a native-IP
link or both. There may be different ways by which to use
a link for TE and non-TE traffic. For example, a link may
be used for both types of traffic and satisfy the TE SLA
requirements, so long as the link is under-subscribed for
TE (say, 50% of the link capacity is being used). Once the
TE capacity requirement exceeds the set mark (say, the 50%
mark), the link may be removed from the non-TE topology.
4. This document does not require any changes to the existing OSPF
LSDB implementation. Rather, it suggests the use of another
database, the TE-LSDB, comprised of the TE LSAs, for TE purposes.
5. As a general rule, all nodes and links that may be party
to a TE circuit should be uniquely identifiable by an IP
address. As for router ID, a separate loopback IP address
for the router, independent of the links attached, is
recommended.
6. The assumption about to be stated is principally meant for
non-packet networks such as a SONET TDM network. In non-packet
networks, each IP subnet on a TE-configurable network MUST have
a minimum of one node with an interface running OSPF-TE protocol.
For example, a SONET/SDH TDM ring must have a minimum of one node
(say, a Gateway Network Element) running the OSPF protocol in
order to enable TE configuration on all nodes within the ring.
An OSPF-TE node may advertise more than itself and the links
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it is directly attached to. It may also advertise other TE
participants and their links, on their behalf.
5.3. Limitations
Below are the limitations of the OSPF-TE.
1. Disjoint TE topologies would have the same problem as an
OSPF-TE node not forming adjacencies with any other node.
The disjoint nodes will not be included in the TE topology
of the rest of the TE routers. It will be the
responsibility of the network administrator(s) to ensure
connectedness of the TE network.
For example, two routers that are physically connected to
the same link (or broadcast network) need not be router
adjacent via the Hello protocol, if the link is not IP
packet terminated.
6. Transition strategy for implementations using Opaque LSAs
Below is a strategy to transition implementations using opaque
LSAs to adapt the new TE LSA scheme in a gradual fashion.
1. Restrict the use of Opaque-LSAs to within an area.
2. Fold in the TE option flag to construct the TE and non-TE
topologies in an area, even if the topologies cannot be used
for flooding within the area.
3. Use TE-Summary LSAs and TE-AS-external-LSAs for inter-area
Communication. Make use of the TE-topology within area to
summarize the TE networks in the area and advertise the same
to all TE-routers in the backbone. The TE-ABRs on the backbone
area will in-turn advertise these summaries again within their
connected areas.
7. The OSPF Options field
A new TE flag is introduced within the options field to identify
TE extensions to the OSPF. This bit will be used to distinguish
between routers that support Traffic engineering extensions and
those that do not. The OSPF options field is present in OSPF
Hello packets, Database Description packets and all link state
advertisements. The TE bit, however, is a requirement only for
the Hello packets. Use of TE-bit is optional in Database
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Description packets or LSAs.
Below is a description of the TE-Bit. Refer [OSPF-V2], [OSPF-NSSA]
and [OPAQUE] for a description of the remaining bits in options
field.
--------------------------------------
|TE | O | DC | EA | N/P | MC | E | * |
--------------------------------------
The OSPF options field - TE support
TE-Bit: This bit is set to indicate support for Traffic Engineering
extensions to the OSPF. The Hello protocol which is used for
establishing router adjacency and bidirectionality of the
link will use the TE-bit to build adjacencies between two
nodes that are either both TE-compliant or not. Two routers
will not become TE-neighbors unless they agree on the state
of the TE-bit. TE-compliant OSPF extensions are advertised
only to the TE-compliant routers. All other routers may
simply ignore the advertisements.
There is however a caveat with the above use of the last remaining
reserved bit in the options field. OSPF v2 will have no more
reserved bits left for future option extensions. If it is deemed
necessary to leave this bit as is, we could use OPAQUE-9 LSA (Local
scope) along each interface to communicate the support for OSPF-TE.
8. Bringing up TE adjacencies; TE vs. Non-TE topologies
OSPF creates adjacencies between neighboring routers for the purpose
of exchanging routing information. In the following subsections, we
describe the use of Hello protocol to establish TE capability
compliance between neighboring routers of an area. Further, the
capability is used as the basis to build a TE vs. non-TE network
topology.
8.1. The Hello Protocol
The Hello Protocol is primarily responsible for dynamically
establishing and maintaining neighbor adjacencies. In a TE network,
it may not be required or possible for all links and neighbors to
establish adjacency using this protocol.
The Hello protocol will use the TE-bit to establish Traffic
Engineering capability (or not) between two OSPF routers.
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For NBMA and broadcast networks, this protocol is responsible for
electing the designated router and the backup designated router.
For a TDM ring network, the designated and backup designated
routers may either be preselected (ex: GNE, backup-GNE) or
determined via the same Hello protocol. In any case, routers
supporting the TE option shall be given a higher precedence for
becoming a designated router over those that do not support TE.
8.2. Flooding and the Synchronization of Databases
In OSPF, adjacent routers within an area must synchronize their
databases. However, as observed in [FLOOD-OPT], the requirement
may be stated more concisely that all routers in an area must
converge on the same link state database. To do that, it suffices
to send single copies of LSAs to the neighboring routers in an
area, rather than send one copy on each of the connected
interfaces. [FLOOD-OPT] describes in detail how to minimize
flooding (Initial LSDB synchronization as well as the
asynchronous LSA updates) within an area.
With the OSPF-TE described here, a TE-only network topology is
constructed based on the TE option flag in the Hello packet.
Subsequent to that, TE LSA flooding in an area is limited to
TE-only routers in the area, and do not impact non-TE routers
in the area. A network may be constituted of a combination of
a TE topology and a non-TE (control) topology. Standard IP
packet forwarding and routing protocols are possible along the
control topology.
In the case where some of the neighbors are TE compliant and
others are not, the designated router will exchange different
sets of LSAs with its neighbors. TE LSAs are exchanged only
with the TE neighbors. Native LSAs do not include description
for TE links. As such, native LSAs are exchanged with all
neighbors (TE and non-TE alike) over a shared non-TE link.
Flooding optimization in a TE network is essential
for two reasons. First, the control traffic for a TE network is
likely to be much higher than that of a non-TE network. Flooding
optimizations help to minimize the announcements and the
associated retransmissions and acknowledgements on the network.
Secondly, the TE nodes need to converge at the earliest to keep
up with TE state changes occurring throughout the TE network.
This process of flooding along a TE topology cannot be folded
into the Opaque-LSA based TE scheme ([OPQLSA-TE]), because
Opaque LSAs (say, LSA #10) have a pre-determined flooding
scope. Even as a TE topology is available from the use of
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TE option flag, the TE topology is not usable for flooding
unless a new TE LSA is devised, whose boundaries can be set to
span the TE-only routers in an area.
NOTE, a new All-SPF-TE Multicast address may be used for the
exchange of TE compliant database descriptors.
8.3. The Designated Router
The Designated Router is elected by the Hello Protocol on broadcast
and NBMA networks. In general, when a router's interface to a
network first becomes functional, it checks to see whether there is
currently a Designated Router for the network. If there is, it
accepts that Designated Router, regardless of its Router Priority,
so long as the current designated router is TE compliant. Otherwise,
the router itself becomes Designated Router if it has the highest
Router Priority on the network and is TE compliant.
Clearly, TE-compliance must be implemented on the most robust
routers only, as they become most likely candidates to take on
additional role as designated router.
Alternatively, there can be two sets of designated routers, one for
the TE compliant routers and another for the native OSPF routers
(non-TE compliant).
8.4. The Backup Designated Router
The Backup Designated Router is also elected by the Hello
Protocol. Each Hello Packet has a field that specifies the
Backup Designated Router for the network. Once again, TE-compliance
must be weighed in conjunction with router priority in determining
the backup designated router. Alternatively, there can be two sets
of backup designated routers, one for the TE compliant routers and
another for the native OSPF routers (non-TE compliant).
8.5. The graph of adjacencies
An adjacency is bound to the network that the two routers have
in common. If two routers have multiple networks in common,
they may have multiple adjacencies between them. The adjacency
may be split into two different types - Adjacency between
TE-compliant routers and adjacency between non-TE compliant
routers. A router may choose to support one or both types of
adjacency.
Two graphs are possible, depending on whether a Designated
Router is elected for the network. On physical point-to-point
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networks, Point-to-MultiPoint networks and virtual links,
neighboring routers become adjacent whenever they can
communicate directly. The adjacency can only be one of
(a) TE-compliant or (b) non-TE compliant. In contrast, on
broadcast and NBMA networks the Designated Router and the
Backup Designated Router may maintain two sets of adjacency.
However, the remaining routers will participate in either
TE-compliant adjacency or non-TE-compliant adjacency, but not
both. In the Broadcast network below, you will notice that
routers RT7 and RT3 are chosen as the designated and backup
routers respectively. Within the network, Routers RT3, RT4
and RT7 are TE-compliant. RT5 and RT6 are not. So, you will
notice the adjacency variation with RT4 vs. RT5 or RT6.
+---+ +---+
|RT1|------------|RT2| o---------------o
+---+ N1 +---+ RT1 RT2
RT7
o::::::::::
+---+ +---+ +---+ /|: :
|RT7| |RT3| |RT4| / | : :
+---+ +---+ +---+ / | : :
| | | / | : :
+-----------------------+ RT5o RT6o oRT4 :
| | N2 * * ; :
+---+ +---+ * * ; :
|RT5| |RT6| * * ; :
+---+ +---+ **; :
o::::::::::
RT3
Figure 6: The graph of adjacencies with TE-compliant routers.
9. TE LSAs
The native OSPF protocol, as of now, has a total of 11 LSA types.
LSA types 1 through 5 are defined in [OSPF-v2]. LSA types 6, 7
and 8 are defined in [MOSPF], [NSSA] and [BGP-OSPF] respectively.
Lastly, LSA types 9 through 11 are defined in [OPAQUE].
Each of the LSA types have a unique flooding scope defined.
Opaque LSA types 9 through 11 are general purpose LSAs, with
flooding scope set to link-local, area-local and AS-wide (except
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stub areas) respectively. As will become apparent from this
document, the general purpose content format and the coarse
flooding scope of Opaque LSAs are not suitable for disseminating
TE data.
In the following subsections, we define new LSAs for Traffic
engineering use. The Values for the new TE LSA types are assigned
such that the high bit of the LS-type octet is set to 1. The new
TE LSAs are largely modeled after the existing LSAs for content
format and have a custom suited flooding scope. Flooding
optimizations discussed in previous sections shall be used to
disseminate TE LSAs along the TE-restricted topology.
A TE-router LSA is defined to advertise TE characteristics
of the router and all the TE-links attached to the TE-router.
TE-Link-Update LSA is defined to advertise individual link
specific TE updates. Flooding scope for both these LSAs is the
TE topology within the area to which the links belong. I.e.,
only those OSPF nodes within the area with TE links will receive
these TE LSAs.
TE-Summary network and router LSAs are defined to advertise
the reachability of area-specific TE networks and Area border
routers(along with router TE characteristics) to external
areas. Flooding Scope of the TE-Summary LSAs is the TE topology
in the entire AS less the non-backbone area for which the
the advertising router is an ABR. Just as with native OSPF
summary LSAs, the TE-summary LSAs do not reveal the topological
details of an area to external areas. But, the two summary LSAs
do differ in some respects. The flooding scope of TE summary
LSAs is different. As for content, TE summary network LSAs
simply describe reachability without summarization of network
access costs. And, unlike the native summary router LSA,
TE-summary router LSA content includes TE capabilities of the
advertising TE router.
TE-AS-external LSA and TE-Circuit-Path LSA are defined to
advertise AS external network reachability and pre-established
TE circuits respectively. While flooding scope for both
these LSAs can be the TE-topology in the entire AS, flooding
scope for the pre-established TE circuit LSA may optionally be
restricted to just the TE topology within an area.
Lastly, the new TE LSAs are defined so as to permit peer
operation of packet networks and non-packet networks alike.
As such, a new TE-Router-Proxy LSA is defined to allow
advertisement of a TE router, that is not OSPF capable, by
an OSPF-TE node as a proxy.
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9.1. TE-Router LSA (0x81)
The TE-router LSA (0x81) is modeled after the router LSA with the
same flooding scope as the router-LSA, except that the scope is
restricted to TE-only nodes within the area. The TE-router LSA
describes the TE metrics of the router as well as the TE-links
attached to the router. Below is the format of the TE-router LSA.
Unless specified explicitly otherwise, the fields carry the same
meaning as they do in a router LSA. Only the differences are
explained below. Router-TE flags, Router-TE TLVs, Link-TE options,
and Link-TE TLVs are each independently described in a separate
sub-section.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 0x81 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |V|E|B| 0 | Router-TE flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router-TE flags (contd.) | Router-TE TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| .... | # of TE links |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | 0 | Link-TE flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link-TE flags (contd.) | Zero or more Link-TE TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
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Option
In TE-capable router nodes, the TE-bit may be set to 1.
The following fields are used to describe each router link (i.e.,
interface). Each router link is typed (see the below Type field).
The Type field indicates the kind of link being described.
Type
A new link type "Positional-Ring Type" (value 5) is defined.
This is essentially a connection to a TDM-Ring. TDM ring network
is different from LAN/NBMA transit network in that, nodes on the
TDM ring do not necessarily have a terminating path between
themselves. Secondly, the order of links is important in
determining the circuit path. Third, the protection switching
and the number of fibers from a node going into a ring are
determined by the ring characteristics. I.e., 2-fiber vs
4-fiber ring and UPSR vs BLSR protected ring.
Type Description
__________________________________________________
1 Point-to-point connection to another router
2 Connection to a transit network
3 Connection to a stub network
4 Virtual link
5 Positional-Ring Type.
Link ID
Identifies the object that this router link connects to.
Value depends on the link's Type. For a positional-ring type,
the Link ID shall be IP Network/Subnet number, just as with a
broadcast transit network. The following table summarizes the
updated Link ID values.
Type Link ID
______________________________________
1 Neighboring router's Router ID
2 IP address of Designated Router
3 IP network/subnet number
4 Neighboring router's Router ID
5 IP network/subnet number
Link Data
This depends on the link's Type field. For type-5 links, this
specifies the router interface's IP address.
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9.1.1. Router-TE flags - TE capabilities of the router
Below is an initial set of definitions. More may be standardized
if necessary. The TLVs are not expanded in the current rev. Will
be done in the follow-on revs. The field imposes a restriction
of no more than 32 flags to describe the TE capabilities of a
router-TE.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L|L|P|T|L|F| |S|S|S|C|
|S|E|S|D|S|S| |T|E|I|S|
|R|R|C|M|C|C| |A|L|G|P|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|<---- Boolean TE flags ------->|<- TE flags pointing to TLVs ->|
Bit LSR
When set, the router is considered to have LSR capability.
Bit LER
When set, the router is considered to have LER capability.
All MPLS border routers will be required to have the LER
capability. When the E bit is also set, that indicates an
AS Boundary router with LER capability. When the B bit is
also set, that indicates an area border router with LER
capability.
Bit PSC
Indicates the node is Packet Switch Capable.
Bit TDM
Indicates the node is TDM circuit switch capable.
Bit LSC
Indicates the node is Lamda switch Capable.
Bit FSC
Indicates the node is Fiber (can also be a non-fiber link
type) switch capable.
Bit STA
Label Stack Depth limit TLV follows. This is applicable only
when the PSC flag is set.
Bit SEL
TE Selection Criteria TLV, supported by the router, follows.
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Bit SIG
MPLS Signaling protocol support TLV follows.
BIT CSPF
CSPF algorithm support TLV follows.
9.1.2. Router-TE TLVs
The following Router-TE TLVs are defined.
TE-selection-Criteria TLV (Tag ID = 1)
The values can be a series of resources that may be used
as the criteria for traffic engineering (typically with the
aid of a signaling protocol such as RSVP-TE or CR-LDP or LDP).
- Bandwidth based LSPs (1)
- Priority based LSPs (2)
- Backup LSP (3)
- Link cost (4)
Bandwidth criteria is often used in conjunction with Packet
Switch Capable nodes. The unit of bandwidth permitted to be
configured may however vary from vendor to vendor. Bandwidth
criteria may also be used in conjunction with TDM nodes. Once
again, the granularity of bandwidth allocation may vary from
vendor to vendor.
Priority based traffic switching is relevant only to Packet
Switch Capable nodes. Nodes supporting this criteria will
be able to interpret the EXP bits on the MPLS header to
prioritize the traffic across the same LSP.
Backup criteria refers to whether or not the node is capable
of finding automatic protection path in the case the
originally selected link fails. Such a local recovery is
specific to the node and may not need to be notified to the
upstream node.
MPLS-Signaling protocol TLV (Tag ID = 3)
The value can be 2 bytes long, listing a combination of
RSVP-TE, CR-LDP and LDP.
Constraint-SPF algorithms-Support TLV (Tag ID = 4)
List all the CSPF algorithms supported. Support for CSPF
algorithms on a node is an indication that the node may be
requested for all or partial circuit path selection during
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circuit setup time. This can be beneficial in knowing
whether or not the node is capable of expanding loose
routes (in an MPLS signaling request) into an LSP. Further,
the CSPF algorithm support on an intermediate node can be
beneficial when the node terminates one or more of the
hierarchical LSP tunnels.
Label Stack Depth TLV (Tag ID = 5)
Applicable only for PSC-Type traffic. A default value of 1
is assumed. This indicates the depth of label stack the
node is capable of processing on an ingress interface.
9.1.3. Link-TE options - TE capabilities of a TE-link
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|T|N|P|T|L|F|D| |S|L|B|C|
|E|T|K|D|S|S|B| |R|U|W|O|
| |E|T|M|C|C|S| |L|G|A|L|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|<---- Boolean TE flags ------->|<- TE flags pointing to TLVs ->|
TE - Indicates whether TE is permitted on the link. A link
can be denied for TE use by setting the flag to 0.
NTE - Indicates whether non-TE traffic is permitted on the
TE link. This flag is relevant only when the TE
flag is set.
PKT - Indicates whether or not the link is capable of
packet termination.
TDM, LSC, FSC bits
- Same as defined for router TE options.
DBS - Indicates whether or not Database synchronization
is permitted on this link.
SRLG Bit - Shared Risk Link Group TLV follows.
LUG bit - Link usage cost metric TLV follows.
BWA bit - Data Link bandwidth TLV follows.
COL bit - Data link Color TLV follows.
9.1.4. Link-TE TLVs
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SRLG-TLV
This describes the list of Shared Risk Link Groups the link
belongs to. Use 2 bytes to list each SRLG.
BWA-TLV
This indicates the maximum bandwidth, available bandwidth,
reserved bandwidth for later use etc. This TLV may also
describe the Data link Layer protocols supported and the
Data link MTU size.
LUG-TLV
This indicates the link usage cost - Bandwidth unit, Unit
usage cost, LSP setup cost, minimum and maximum durations
permitted for setting up the TLV etc., including any time
of day constraints.
COLOR-TLV
This is similar to the SRLG TLV, in that an autonomous
system may choose to issue colors to link based on a
certain criteria. This TLV can be used to specify the
color assigned to the link within the scope of the AS.
9.2. TE-incremental-link-Update LSA (0x8d)
A significant difference between a non-TE OSPF network and a TE OSPF
network is that the latter is subject to dynamic circuit pinning and
is more likely to undergo state updates. Specifically, some links
might undergo changes more frequently than others. Advertising the
entire TE-router LSA in response to a change in any single link
could be repetitive. Flooding the network with TE-router LSAs at the
aggregated speed of all the dynamic changes is simply not desirable.
The TE-incremental-link-update LSA advertises only the incremental
link updates.
The TE-incremental-link-Update LSA will be advertised as frequently
as the link state is changed. The TE-link sequence is largely the
advertisement of a sub-portion of router LSA. The sequence number on
this will be incremented with the TE-router LSA's sequence as the
basis. When an updated TE-router LSA is advertised within 30 minutes
of the previous advertisement, the updated TE-router LSA will assume
a sequence no. that is larger than the most frequently updated of
its links.
Below is the format of the TE-incremental-link-update LSA.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 0x8d |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID (same as Link ID) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | 0 | Link-TE options |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link-TE options | Zero or more Link-TE TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| # TOS | metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TOS | 0 | TOS metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Link State ID
This would be exactly the same as would have been specified as
as Link ID for a link within the router-LSA.
Link Data
This specifies the router ID the link belongs to. In majority of
cases, this would be same as the advertising router. This choice
for Link Data is primarily to facilitate proxy advertisement for
incremental link updates.
Say, a router-proxy-LSa was used to advertise the TE-router-LSA
of a SONET/TDM node. Say, the proxy router is now required to
advertise incremental-link-update for the same SONET/TDM node.
Specifying the actual router-ID the link in the
incremental-link-update-LSA belongs to helps receiving nodes in
finding the exact match for the LSA in their database.
The tuple of (LS Type, LSA ID, Advertising router) uniquely identify
the LSA and replace LSAs of the same tuple with an older sequence
number. However, there is an exception to this rule in the context
of TE-link-update LSA. TE-Link update LSA will initially assume the
sequence number of the TE-router LSA it belongs to. Further, when a
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new TE-router LSA update with a larger sequence number is advertised,
the newer sequence number is assumed by al the link LSAs.
9.3. TE-Circuit-paths LSA (0x8C)
TE-Circuit-paths LSA may be used to advertise the availability of
pre-established TE circuit path(s) originating from any router
in the network. The flooding scope may be Area wide or AS wide.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 0x84 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |G|E|B|D|S|T|CktType| Circuit Duration (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Circuit Duration cont... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Circuit Duartion cont.. | Circuit Setup time (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Circuit Setup time cont... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Circuit Setup time cont.. |Circuit Teardown time(Optional)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Circuit Teardown time cont... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Circuit Teardown time cont.. | No. of TE circuit paths |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Circuit-TE ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Circuit-TE Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | 0 | Circuit-TE flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Circuit-TE flags (contd.) | Zero or more Circuit-TE TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Circuit-TE ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Circuit-TE Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| ... |
Link State ID
The ID of the far-end router or the far-end Link-ID to which the
TE circuit path(s) is being advertised.
TE-circuit-path(s) flags
Bit G - When set, the flooding scope is set to be AS wide.
Otherwise, the flooding scope is set to be area wide.
Bit E - When set, the advertised Link-State ID is an AS boundary
router (E is for external). The advertising router and
the Link State ID belong to the same area.
Bit B - When set, the advertised Link state ID is an Area border
router (B is for Border)
Bit D - When set, this indicates that the duration of circuit
path validity follows.
Bit S - When set, this indicates that Setup-time of the circuit
path follows.
Bit T - When set, this indicates that teardown-time of the
circuit path follows.
CktType
This 4-bit field specifies the Circuit type of the Forward
Equivalency Class (FC).
0x01 - Origin is Router, Destination is Router.
0x02 - Origin is Link, Destination is Link.
0x04 - Origin is Router, Destination is Link.
0x08 - Origin is Link, Destination is Router.
Circuit Duration (Optional)
This 64-bit number specifies the seconds from the time of the
LSA advertisement for which the adversited pre-established
TE circuit path will be valid. This field is specified only
when the D-bit is set in the TE-circuit-path flags.
Circuit Setup time (Optional)
This 64-bit number specifies the time at which the TE-circuit
path may be setup. This field is specified only when the
S-bit is set in the TE-circuit-path flags. The setup time is
specified as the number of seconds from the start of January
1 1970 UTC.
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Circuit Teardown time (Optional)
This 64-bit number specifies the time at which the TE-circuit
path may be torn down. This field is specified only when the
T-bit is set in the TE-circuit-path flags. The teardown time
is specified as the number of seconds from the start of
January 1 1970 UTC.
No. of TE Circuit paths
This indicates the number of pre-established TE circuit paths
between the advertising router and the router specified in the
link state ID.
Circuit-TE ID
This is the ID of the far-end router for a given TE-circuit
path segment.
Circuit-TE Data
This is the virtual link identifier on the near-end router for
a given TE-circuit path segment. This can be a private
interface or handle the near-end router uses to identify the
virtual link.
The sequence of (circuit-TE ID, Circuit-TE Data) list the
end-point nodes and links in the LSA as a series.
Circuit-TE flags
This lists the Zero or more TE-link TLVs that all member
elements of the LSP meet.
9.4. TE-Summary LSAs
TE-Summary-LSAs are the Type 0x83 and 0x84 LSAs. These LSAs are
originated by area border routers. TE-Summary-network-LSA (0x83)
describes the reachability of TE networks in a non-backbone
area, advertised by the Area Border Router. Type 0x84
summary-LSA describes the reachability of Area Border Routers
and AS border routers and their TE capabilities.
One of the benefits of having multiple areas within an AS is
that frequent TE advertisements within the area do not impact
outside the area. Only the TE abstractions as befitting the
external areas are advertised.
9.4.1. TE-Summary Network LSA (0x83)
TE-summary network LSA may be used to advertise reachability of
TE-networks accessible to areas external to the originating
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area. The content and the flooding scope of a TE-Summary LSA
is different from that of a native summary LSA.
The scope of flooding for a TE-summary network is AS wide, with
the exception of the originating area and the stub areas. The
area border router for each non-backbone area is responsible
for advertising the reachability of backbone networks into the
area.
Unlike a native-summary network LSA, TE-summary network LSA does
not advertise summary costs to reach networks within an area.
This is because, TE parameters are not necessarily additive or
comparative. The parameters can be varied in their expression.
A TE-summary network LSA will not be know to summarize a
network whose links do not fall under an SRLG (Shared-Risk Link
Group). This is way, the TE-summary LSA merely advertises the
reachable of TE networks within an area. The specific circuit
paths can be computed by the BDRs. On the other hand, if there
are specific circuit paths to advertise, that can be done
independently using TE-Circuit-path LSA (refer: section 9.3)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 0x83 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID (IP Network Number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router (Area Border Router) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Area-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
9.4.2. TE-Summary router LSA (0x84)
TE-summary router LSA may be used to advertise the availability of
Area Border Routers (ABRs) and AS Border Routers (ASBRs) that are
TE capable. The TE-summary router LSAs are originated by the Area
Border Routers. The scope of flooding for the TE-summary router LSA
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is the non-backbone area the advertising ABR belongs to.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 0x84 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router (ABR) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |E|B| 0 | No. of Areas |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Area-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router-TE flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router-TE TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Link State ID
The ID of the Area border router or the AS border router whose
TE capability is being advertised.
Advertising Router
The ABR that advertises its TE capabilities (and the OSPF areas
it belongs to) or the TE capabilities of an ASBR within one of
the areas the ABR is a border router of.
No. of Areas
Specifies the number of OSPF areas the link state ID belongs to.
Area-ID
Specifies the OSPF area(s) the link state ID belongs to. When
the link state ID is same as the advertising router ID, this
lists all the areas the ABR belongs to. In the case the
link state ID is an ASBR, this simply lists the area the
ASBR belongs to. The advertising router is assumed to be the
ABR from the same area the ASBR is located in.
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Summary-router-TE flags
Bit E - When set, the advertised Link-State ID is an AS boundary
router (E is for external). The advertising router and
the Link State ID belong to the same area.
Bit B - When set, the advertised Link state ID is an Area
border router (B is for Border)
Router-TE flags,
Router-TE TLVs (TE capabilities of the link-state-ID router)
TE Flags and TE TLVs are as applicable to the ABR/ASBR
specified in the link state ID. The semantics is same as
specified in the Router-TE LSA.
9.5. TE-AS-external LSAs (0x85)
TE-AS-external-LSAs are the Type 0x85 LSAs. This is modeled after
AS-external LSA format and flooding scope. These LSAs are originated
by AS boundary routers with TE extensions (say, a BGP node which can
communicate MPLS labels across to external ASes), and describe
networks and pre-established TE links external to the AS. The
flooding scope of this LSA is similar to that of an AS-external LSA.
I.e., AS wide, with the exception of stub areas.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 0x85 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Forwarding address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Route Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| # of Virtual TE links | 0 |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link-TE flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link-TE TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TE-Forwarding address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Route TE Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
Network Mask
The IP address mask for the advertised TE destination. For
example, this can be used to specify access to a specific
TE-node or TE-link with an mask of 0xffffffff. This can also
be used to specify access to an aggregated set of destinations
using a different mask, ex: 0xff000000.
Link-TE flags,
Link-TE TLVs
The TE attributes of this route. These fields are optional and
are provided only when one or more pre-established circuits can
be specified with the advertisement. Without these fields,
the LSA will simply state TE reachability info.
Forwarding address
Data traffic for the advertised destination will be forwarded to
this address. If the Forwarding address is set to 0.0.0.0, data
traffic will be forwarded instead to the LSA's originator (i.e.,
the responsible AS boundary router).
External Route Tag
A 32-bit field attached to each external route. This is not
used by the OSPF protocol itself. It may be used to communicate
information between AS boundary routers; the precise nature of
such information is outside the scope of this specification.
9.6. Changes to Network LSA
Network-LSA is the Type 2 LSA. With the exception of the following,
no additional changes will be required to this LSA for TE
compatibility. The LSA format and flooding scope remains unchanged.
A network-LSA is originated for each broadcast, NBMA and
Positional-Ring type network in the area which supports two or
more routers. The TE option is also required to be set while
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propagating the TDM network LSA.
9.6.1. Positional-Ring type network LSA - New Network type for TDM-ring.
- Ring ID: (Network Address/Mask)
- No. of elements in the ring (a.k.a. ring neighbors)
- Ring Bandwidth
- Ring Protection (UPSR/BLSR)
- ID of individual nodes (Interface IP address)
- Ring type (2-Fiber vs. 4-Fiber, SONET vs. SDH)
Network LSA will be required for SONET RING. Unlike the broadcast
type, the sequence in which the NEs are placed on a RING-network
is pertinent. The nodes in the ting must be described clock wise,
assuming the GNE as the starting element.
9.7. TE-Router-Proxy LSA (0x8e)
This is a variation to the TE-router LSA in that the TE-router LSA
is not advertised by the network element, but rather by a trusted
TE-router Proxy. This is typically the scenario in a non-packet
TE network, where some of the nodes do not have OSPF functionality
and count on a helper node to do the advertisement for them. One
such example would be the SONET/SDH ADM nodes in a TDM ring. The
nodes may principally depend upon the GNE (Gateway Network Element)
to do the advertisement for them. TE-router-Proxy LSA shall not be
used to advertise Area Border Routers and/or AS border Routers.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 0x8e |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID (Router ID of the TE Network Element) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 | Router-TE flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router-TE flags (contd.) | Router-TE TLVs |
+---------------------------------------------------------------+
| .... |
+---------------------------------------------------------------+
| .... | # of TE links |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | 0 | Link-TE options |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link-TE flags | Zero or more Link-TE TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
9.8. Others
We may also introduce a new TE-NSSA LSA, similar to the native-NSSA
LSA. TE-NSSA will help ensure that not all external TE routes are
flooded into the NSSA area. A TE capable router can become the NSSA
translator. All parameters and contents of TE-NSSA LSAs are
transferred as is.
10. Abstract topology representation with TE support
Below, we assume a TE network that is composed of three OSPF areas,
namely Area-1, Area-2 and Area-3, attached together through the
backbone area. The following figure is an inter-area topology
abstraction from the perspective of routers in Area-1. The
abstraction is similar, but not the same, as that of the non-TE
abstraction. As such, the authors claim the model is easy to
understand and emulate. The abstraction illustrates reachability
of TE networks and nodes in areas external to the local area and
ASes external to the local AS. The abstraction also illustrates
pre-established TE links that may be advertised by ABRs and ASBRs.
Area-1 an has a single border router, ABR-A1 and no ASBRs. Area-2
has an Area border router ABR-A2 and an AS border router ASBR-S1.
Area-3 has two Area border routers ABR-A2 and ABR-A3; and an AS
border router ASBR-S2. There may be any number of Pre-engineered
TE links amongst ABRs and ASBRs. The following example assumes a
single TE-link between ABR-A1 and ABR-A2; between ABR-A1 and
ABR-A3; between ABR-A2 to ASBR-S1; and between ABR-A3 to ASBR-S2.
All Area border routers and AS border routers are assumed to
be represented by their TE capabilities.
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+-------+
|Area-1 |
+-------+
+-------------+ |
|Reachable TE | +------+
|networks in |--------|ABR-A1|
|backbone area| +------+
+-------------+ | | |
+-------------+ | +-------------------+
| | |
+-----------------+ | +-----------------+
|Pre-engineered TE| +----------+ |Pre-engineered TE|
|circuit path(s) | | Backbone | |circuit path(s) |
|to ABR-A2 | | Area | |to ABR-A3 |
+-----------------+ +----------+ +-----------------+
| | | |
+----------+ | | |
| | +--------------+ |
+-----------+ | | | | +-----------+
|Reachable | +------------+ +------+ |Reachable |
|TE networks|---| ABR-A2 | |ABR-A3|--|TE networks|
|in Area A2 | +------------+ +------+ |in Area A3 |
+-----------+ / | | | | | +-----------+
/ | | +-------------------+ | +----------+
/ | +-------------+ | | |
+-----------+ +--------------+ | | | +--------------+
|Reachable | |Pre-engineered| | | | |Pre-engineered|
|TE networks| |TE Ckt path(s)| +------+ +------+ |TE Ckt path(s)|
|in Area A3 | |to ASBR-S1 | |Area-2| |Area-3| |to ASBR-S2 |
+-----------+ +--------------+ +------+ +------+ +--------------+
| / | /
+-------------+ | / | /
|AS external | +---------+ +-------------+
|TE-network |------| ASBR-S1 | | ASBR-S2 |
|reachability | +---------+ +-------------+
|from ASBR-S1 | | | |
+-------------+ | | |
+-----------------+ +-------------+ +-----------------+
|Pre-engineered TE| |AS External | |Pre-engineered TE|
|circuit path(s) | |TE-Network | |circuit path(s) |
|reachable from | |reachability | |reachable from |
|ASBR-S1 | |from ASBR-S2 | |ASBR-S2 |
+-----------------+ +-------------+ +-----------------+
Figure 9: Inter-Area Abstraction as viewed by Area-1 TE-routers
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11. Changes to Data structures in OSPF-TE nodes
11.1. Changes to Router data structure
The router with TE extensions must be able to include all the
TE capabilities (as specified in section 7.1) in the router data
structure. Further, routers providing proxy service to other TE
routers must also track the router and associated interface data
structures for all the TE client nodes for which the proxy
service is being provided. Presumably, the interaction between
the Proxy server and the proxy clients is out-of-band.
11.2. Two set of Neighbors
Two sets of neighbor data structures will need to be maintained.
TE-neighbors set is used to advertise TE LSAs. Only the TE-nodes
will be members of the TE-neighbor set. Native neighbors set will
be used to advertise native LSAs. All neighboring nodes supporting
non-TE links can be part of this set. As for flooding optimizations
based on neighbors set, readers may refer [FLOOD-OPT].
11.3. Changes to Interface data structure
The following new fields are introduced to the interface data
structure. These changes are in addition to the changes specified
in [FLOOD-OPT].
TePermitted
If the value of the flag is TRUE, the interface is permissible
to be advertised as a TE-enabled interface.
NonTePermitted
If the value of the flag is TRUE, the interface permits non-TE
traffic on the interface. Specifically, this is applicable to
packet networks, where data links may permit both TE and non-TE
packets. For FSC and LSC TE networks, this flag will be set to
FALSE. For Packet networks that do not permit non-TE traffic on
TE links also, this flag is set to TRUE.
PktTerminated
If the value of the flag is TRUE, the interface terminates
Packet data and hence may be used for IP and OSPF data exchange.
AdjacencySychRequired
If the value of the flag is TRUE, the interface may be used to
synchronize the LSDB across all adjacent neighbors. This is
TRUE by default to all PktTerminated interfaces that are
enabled for OSPF. However, it is possible to set this to FALSE
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for some of the interfaces.
TE-TLVs
Each interface may potentially have a maximum of 16 TLVS that
describe the link characteristics.
The following existing fields in Interface data structure will take
on additional values to support TE extensions.
Type
The OSPF interface type can also be of type "Positional-RING".
The Positional-ring type is different from other types (such
as broadcast and NBMA) in that the exact location of the nodes
on the ring is relevant, even as they are all on the same
ring. SONET ADM ring is a good example of this. Complete ring
positional-ring description may be provided by the GNE on a
ring as a TE-network LSA for the ring.
List of Neighbors
The list may be statically defined for an interface, without
requiring the use of Hello protocol.
12. IANA Considerations
12.1. TE-compliant-SPF routers Multicast address allocation
12.2. New TE-LSA Types
12.3. New TLVs (Router-TE and Link-TE TLVs)
12.3.1. TE-selection-Criteria TLV (Tag ID = 1)
- Bandwidth based LSPs (1)
- Priority based LSPs (2)
- Backup LSP (3)
- Link cost (4)
12.3.2. MPLS-Signaling protocol TLV (Tag ID = 3)
- RSVP-TE signaling
- LDP signaling
- CR-LDP signaling
12.3.3. Constraint-SPF algorithms-Support TLV (Tag ID = 4)
- CSPF Algorithm Codes.
12.3.4. SRLG-TLV (Tag ID = 0x81)
- SRLG group IDs
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12.3.5. BW-TLV (Tag ID = 0x82)
12.3.6 CO-TLV (Tag ID = 0x83)
13. Acknowledgements
The authors wish to thank Vishwas Manral, Chitti Babu, Riyad
Hartani and Tricci So for their valuable comments and feedback
on the draft.
14. Security Considerations
This memo does not create any new security issues for the OSPF
protocol. Security considerations for the base OSPF protocol are
covered in [OSPF-v2]. As a general rule, a TE network is likely
to generate significantly more control traffic than a native
OSPF network. The excess traffic is almost directly proportional
to the rate at which TE circuits are setup and torn down within
an autonomous system. It is important to ensure that TE database
synchronizations happen quickly when compared to the aggregate
circuit setup an tear-down rates.
REFERENCES
[IETF-STD] Bradner, S., " The Internet Standards Process --
Revision 3", RFC 1602, IETF, October 1996.
[RFC 1700] J. Reynolds and J. Postel, "Assigned Numbers",
RFC 1700
[MPLS-TE] Awduche, D., et al, "Requirements for Traffic
Engineering Over MPLS," RFC 2702, September 1999.
[GMPLS-TE] P.A. Smith et. al, "Generalized MPLS - Signaling
Functional Description", work in progress,
draft-ietf-mpls-generalized-signaling-03.txt
[RSVP-TE] Awduche, D., L. Berger, D. Gan, T. Li, V. Srinivasan,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC3209, IETF, December 2001
[CR-LDP] Jamoussi, B. et al, "Constraint-Based LSP Setup
using LDP", draft-ietf-mpls-cr-ldp-06.txt,
Work in Progress.
Srisuresh & Joseph [Page 41]
Internet-Draft OSPF TE extensions September 2002
[OSPF-v2] Moy, J., "OSPF Version 2", RFC 2328, April 1998.
[MOSPF] Moy, J., "Multicast Extensions to OSPF", RFC 1584,
March 1994.
[NSSA] Coltun, R., V. Fuller and P. Murphy, "The OSPF NSSA
Option", draft-ietf-ospf-nssa-update-10.txt, Work in
Progress.
[OPAQUE] Coltun, R., "The OSPF Opaque LSA Option," RFC 2370,
July 1998.
[FLOOD-OPT] Zinin, A. and M. Shand, "Flooding Optimizations in
link-state routing protocols", work in progress,
<draft-ietf-ospf-isis-flood-opt-01.txt>
[OPQLSA-TE] Katz, D., D. Yeung and K. Kompella, "Traffic
Engineering Extensions to OSPF", work in progress,
<draft-katz-yeung-ospf-traffic-06.txt>
[OPQLSA-GMPLS] Kompella, K., Y. Rekhter, A. Banerjee, J. Drake,
G. Bernstein, D. Fedyk, E. Mannie, D. Saha and
V. Sharma, "OSPF Extensions in Support of Generalized
MPLS", <draft-ietf-ccamp-ospf-gmpls-extensions-01.txt>,
work in progress.
Authors' Addresses
Pyda Srisuresh
Kuokoa Networks, Inc.
475 Potrero Avenue
Sunnyvale, CA 94085
U.S.A.
EMail: srisuresh@yahoo.com
Paul Joseph
Force10 Networks
1440 McCarthy Boulevard
Milpitas, CA 95035
U.S.A.
EMail: pjoseph@Force10Networks.com
Srisuresh & Joseph [Page 42]