Network Working Group P. Srisuresh
INTERNET-DRAFT Kuokoa Networks
Expires as of June 8, 2003 P. Joseph
Force10 Networks
December 8, 2002
OSPF-TE: An experimental extension to OSPF for Traffic Engineering
<draft-srisuresh-ospf-te-04.txt>
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Abstract
This document defines OSPF-TE, an experimental traffic engineering
(TE) extension to the link-state routing protocol OSPF. New TE
LSAs are designed to disseminate TE metrics within an autonomous
System (AS) - intra-area as well as inter-area. An Autonomous
System may consist of TE and non-TE nodes. Non-TE nodes are
uneffected by the distribution of TE LSAs. A stand-alone TE Link
State Database (TE-LSDB), separate from the native OSPF LSDB, is
generated for the computation of TE circuit paths. OSPF-TE is
also extendible to non-packet networks such as SONET/TDM and
optical networks. A transition path is provided for those
currently using [OPQLSA-TE] and wish to adapt OSPF-TE.
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Table of Contents
1. Introduction ................................................3
2. Principles of traffic engineering ...........................3
3. Terminology .................................................5
3.1. TE node ................................................5
3.2. TE link ................................................5
3.3. TE circuit path ........................................5
3.4. OSPF-TE node ...........................................6
3.5. TE control network .....................................6
3.6. TE network (TE topology) ...............................6
3.7. Packet-TE network ......................................6
3.8. Non-packet-TE network ..................................6
3.9. Native (non-TE) node ...................................7
3.10. Native (non-TE) link ..................................7
3.11. Non-TE network (Non-TE topology) ......................7
3.12. Peer network (combination network) ....................7
3.13. LSP ...................................................7
3.14. LSA ...................................................7
3.14. LSDB ..................................................7
3.15. CSPF ..................................................7
3.16. TLV ...................................................8
3.17. Router-TE TLVs ........................................8
3.18. Link-TE TLVs ..........................................8
4. Motivations behind the design of OSPF-TE ....................8
4.1. Scalable design ........................................9
4.2. Coexistent design ......................................9
4.3. Efficient in flooding reach ............................9
4.4. Ability to reserve TE-exclusive links .................10
4.5. Extendible design .....................................10
4.6. Unified for packet and non-packet networks ............11
4.7. Networks benefiting from the OSPF-TE design ...........11
5. OSPF-TE solution overview ..................................12
5.1. OSPF-TE Solution ......................................12
5.2. Assumptions ...........................................13
6. Opaque LSAs to OSPF-TE transition strategy .................14
7. OSPF-TE router adjacency - TE topology discovery ...........14
7.1. The OSPF Options field ................................15
7.2. The Hello Protocol ....................................15
7.3. Flooding and the Synchronization of Databases .........16
7.4. The Designated Router .................................16
7.5. The Backup Designated Router ..........................16
7.6. The graph of adjacencies ..............................17
8. TE LSAs - Packet network ...................................18
8.1. TE-Router LSA (0x81) ..................................19
8.2. TE-incremental-link-Update LSA (0x8d) .................26
8.3. TE-Circuit-paths LSA (0x8C) ...........................27
8.4. TE-Summary LSAs .......................................30
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8.5. TE-AS-external LSAs (0x85) ............................33
9. TE LSAs - Non-packet network ...............................34
9.1. TE-Router LSA (0x81) ..................................34
9.2. Changes to Network LSA ................................36
9.3. TE-Router-Proxy LSA (0x8e) ............................36
10. Abstract topology representation with TE support ...........37
11. Changes to Data structures in OSPF-TE routers ..............40
11.1. Changes to Router data structure .....................40
11.2. Two set of Neighbors .................................40
11.3. Changes to Interface data structure ..................40
12. IANA Considerations ........................................41
12.1. TE LSA type values ...................................41
12.2. TE TLV tag values ....................................42
13. Acknowledgements ...........................................42
14. Security Considerations ....................................42
15. Normative References .......................................44
16. Informative References .....................................44
1. Introduction
This document defines OSPF-TE, an experimental traffic engineering
(TE) extension to the link-state routing protocol OSPF. The
objective of OSPF-TE is to discover TE network topology and
disseminate TE metrics within an autonomous system(AS). A
stand-alone TE Link State Database (TE-LSDB), different from
the native OSPF LSDB, is created to facilitate computation of TE
circuit paths. Algorithms to compute TE circuit paths is however
not the objective of this document.
OSPF-TE is different from the Opaque-LSA-based design outlined
in [OPQLSA-TE]. Section 4 describes the motivations behind the
design of OSPF-TE. Section 6 outlines a strategy to transition
Opaque-LSA based implementations to adapt OSPF-TE.
Those interested in TE extensions for the packet networks only
may skip section 9.0.
2. Principles of traffic engineering
The objective of traffic engineering is to set up circuit
path(s) between a pair of nodes or links and to forward traffic
of a certain forwarding equivalency class through the circuit
path. Only the unicast circuit paths are considered here.
Multicast variations are out of scope for this document.
A traffic engineered circuit path may be identified by the
tuple of (Forwarding Equivalency Class, TE parameters for the
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circuit, Origin Node/Link, Destination node/Link).
Forwarding Equivalency Class (FEC) is a grouping of traffic
that is forwarded in the same manner by a node. A FEC may be
classified based on a number of criteria as follows.
a) Traffic arriving on a specific interface,
b) Traffic arriving at a certain time of day,
c) Traffic meeting a certain classification criteria
(ex: based on a match of the fields in the IP and
transport headers),
d) Traffic in a certain priority class,
e) Traffic arriving on a specific set of TDM (STS) circuits
on an interface,
f) Traffic arriving on a certain wavelength of an interface
Discerning traffic based on the FEC criteria is mandatory for
Label Edge Routers (LERs). The intermediate Label Switched Routers
(LSRs) are transparent to the traffic content. LSRs are merely
responsible for keeping the circuit in-tact for the circuit
lifetime. This document will not address defining FEC criteria,
or the mapping of a FEC to circuit, or the associated signaling to
set up circuits. [MPLS-TE] and [GMPLS-TE] address the FEC criteria.
[RSVP-TE] and [CR-LDP] address signaling protocols to set up
circuits.
This document is concerned with the collection of TE metrics for
all the TE enforceable nodes and links within an autonomous system.
TE metrics for a node may include the following.
a) Ability to perform traffic prioritization,
b) Ability to provision bandwidth on interfaces,
c) Support for Constrained Shortest Path First (CSPF)
algorithms,
d) Support for certain TE-Circuit switch type,
e) Support for a certain type of automatic protection
switching
TE metrics for a link may include the following.
a) Available bandwidth,
b) Reliability of the link,
c) Color assigned to the link,
d) Cost of bandwidth usage on the link,
e) Membership to a Shared Risk Link Group (SRLG)
A number of CSPF algorithms may be used to dynamically set up
TE circuit paths in a TE network.
As for origin node/link and destination node/link, the originating
and the terminating entities of a TE circuit path are identifiable
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by their IP addresses.
3. Terminology
Definitions of terms used in the context of the 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 [IETF-STD].
Below are definitions for the terms used within this document.
3.1. TE node
TE-Node is a node in the traffic engineered (TE) network. A
TE-node has a minimum of one TE-link attached to it. Associated
with each TE node is a set of supported TE metrics. A TE node
may also participate in a native IP network.
In a SONET/TDM or photonic cross-connect network, a TE node is
not required to be an OSPF-TE router. An external OSPF-TE router
may act as proxy for the TE nodes that cannot be routers
themselves.
3.2. TE link
TE Link is a network attachment point to a TE-node and is
intended for traffic engineering use. Associated with each
TE link is a set of supported TE metrics. A TE link may also
optionally carry native IP traffic.
Of the various links attached to a TE-node, only the links that
take part in a traffic engineered network are called the TE
links.
3.3. TE circuit path
A TE circuit path is a uni-directional data path, defined by a
list of TE nodes connected to each other through TE links. A
TE circuit path is also often referred merely as a circuit path
or a circuit.
For the purposes of OSPF-TE, the originating and terminating
entities of a TE circuit path must be identifiable by their
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IP addresses. As a general rule, all nodes and links party to a
Traffic Engineered network should be uniquely identifiable by an
IP address.
3.4. OSPF-TE node
An OSPF-TE node is a TE node that runs the OSPF routing protocol
and the OSPF-TE extensions described in this document.
An autonomous system (AS) may be constituted of a combination of
native and OSPF-TE nodes.
3.5. TE Control network
The IP network used by the OSPF-TE nodes for OSPF-TE
communication is referred as the TE control network or simply
the control network. The control network can be independent of
the TE data network.
3.6. TE network (TE topology)
A TE network is a network of connected TE-nodes and TE-links
for the purpose of setting up one or more TE circuit paths.
The terms TE network, TE data network and TE topology are
used synonymously throughout the document.
3.7. Packet-TE network
A packet-TE network is a TE network in which the nodes switch
MPLS packets. An MPLS packet is defined in [MPLS-TE] as a
packet with an MPLS header, followed by data octets. The
intermediary node(s) of a circuit path in a packet-TE network
perform MPLS label swapping to emulate the circuit.
Unless specified otherwise, the term packet network is used
throughout the document to refer a packet-TE network.
3.8. Non-packet-TE network
A non-packet-TE network is TE-network in which the nodes
switch non-packet entities such as an STS time slot, a Lambda
wavelength or simply an interface.
SONET/TDM and Fiber cross-connect networks are examples of
non-packet-TE networks. Circuit emulation in these networks
is accomplished by the switch fabric in the intermediary
nodes (based on TDM time slot, fiber interface or Lambda).
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Unless specified otherwise, the term non-packet network is
used throughout the document to refer a non-packet-TE
network.
3.9. Native (non-TE) node
A native or non-TE node is an OSPF router capable of IP packet
forwarding and does not take part in a TE network. A native
OSPF node forwards IP traffic using the shortest-path
forwarding algorithm and does not run the OSPF-TE extensions.
3.10. Native (non-TE) link
A native (or non-TE) link is a network attachment to a TE or
non-TE node used for IP packet traversal.
3.11. non-TE network (Non-TE topology)
A non-TE network refers to an OSPF network that does not
support TE. Non-TE network, native-OSPF network and non-TE
topology are used synonymously throughout the document.
3.12. Peer network (combination network)
A peer network is a network that is constituted of packet
and non-packet networks combined. In a peer network, a TE
node could potentially support TE links for the packet as
well as non-packet data.
OSPF-TE is usable within a packet network or a non-packet
network or a peer network, which is a combination of the two.
3.13. LSP
LSP stands for "Label Switched Path". LSP is a TE circuit path
in a packet network. The terms LSP and TE circuit path are
used synonymously in the context of packet networks.
3.14. LSA
LSA stands for OSPF "Link State Advertisement".
3.15. LSDB
LSDB stands for "LSA Database". LSDB is a representation of the
topology of a network. A native LSDB, constituted of native OSPF
LSAs, represents the topology of a native IP network. TE-LSDB, on
the other hand, is constituted of TE LSAs and is a representation
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of the TE network topology.
3.16. CSPF
CSPF stands for "Constrained Shortest Path First". Given a TE
LSDB and a set of constraints that must be satisfied to form a
circuit path, there may be several CSPF algorithms to obtain a
TE circuit path that meets the criteria.
3.17. 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 octets required for Tag and Length specification.
All TLVs described in this document are padded to 32-bit
alignment. Any padding required for alignment will not be a part
of the length field, however. TLVs are used to describe traffic
engineering characteristics of the TE nodes, TE links and TE circuit
paths.
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 .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3.18. Router-TE TLVs
TLVs used to describe the TE capabilities of a TE-node.
3.19. Link-TE TLVs
TLVs used to describe the TE capabilities of a TE-link.
4. Motivations behind the design of OSPF-TE
There are several motivations that lead to the design of OSPF-TE.
OSPF-TE is scalable, coexistent and efficient in flooding reach.
The motivations are explained in detail in the following
subsections. Also listed in the last subsection are network
scenarios that benefit from the OSPF-TE design.
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4.1. Scalable design
Area level abstraction provides the scaling necessary for a large
autonomous system (AS). OSPF-TE allows for independent area
abstractions for the TE and native topologies. The TE and native
area border routers will advertise different summary LSAs to TE
and non-TE routers. Readers may refer section 10 for a
topological view of the AS from an OSPF-TE node in an area.
4.2. Coexistent design
OSPF-TE regards an AS as constituted of a TE and non-TE networks
coexisting within the same bounds. OSPF-TE dynamically discovers
TE topology and the associated TE metrics of the nodes and links
within, just as the native OSPF does in a non-TE network. An
independent TE-LSDB, representative of the TE topology is
generated as a result. A stand-alone TE-LSDB allows for speedy
searches through the database.
In [OPQLSA-TE], the TE-LSDB is derived from the combination of
opaque LSAs and native LSDB. The TE-LSDB derived has no
knowledge of the TE capabilities of the routers in the network.
4.3. Efficient in 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. Non-TE
nodes are not bombarded with TE LSAs. This is a useful
characteristic for networks supporting native and TE traffic in
the same connected network.
A subset of the TE metrics may be prone to rapid change, while
others remain largely unchanged. Changes in TE metrics must be
communicated at the earliest throughout the network to ensure
that the TE-LSDB is up-to-date within the network. 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 set up and torn down within the TE network. The TE database
synchronization should occur much quicker compared to the
aggregate circuit set up and tear-down rates.
TE-Incremental-Link-update LSA (section 8.2) permits advertising
a subset of the link metrics.
The more frequent and wider the flooding frequency, the larger
the number of retransmissions and acknowledgements. The same
information (needed or not) may reach a router through multiple
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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.
It is undesirable to flood non-TE nodes with TE information.
[OPQLSA-TE] uses Opaque LSAs for advertising TE information.
Opaque LSAs reach all nodes within the network - TE-nodes and
non-TE nodes alike. [OPQLSA-TE] also 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.
4.4. Ability to reserve TE-exclusive links
OSPF-TE is designed to draw distinction between TE-links and
non-TE links. A TE link, configured to support TE traffic
alone, will not permit best-effort IP traffic on the link.
This permits TE enforceability on the TE links.
When links of a TE-topology do not overlap the links of a
native IP network, OSPF-TE allows for virtual isolation of
the two networks. Best-effort IP transit network and
constraint based TE network often have different service
requirements. 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 service enforceability
can be retained.
[OPQLSA-TE] does not support the ability to isolate best-
effort IP traffic from TE traffic on a link. All links are
subject to best-effort IP traffic. An OSPF router could
potentially select a TE link to be its least cost link and
inundate the link with best-effort IP traffic, thereby
rendering the link unusable for TE purposes.
4.5. Extendible design
OSPF-TE design is based on the tried and tested OSPF paradigm,
and inherits all the benefits of the OSPF, present and future.
TE-LSAs are extendible, just as the native OSPF on which OSPF-TE
is founded.
[OPQLSA-TE], on the other hand, is constrained by the semantics
of the Opaque LSA on which it is founded. The content within an
Opaque LSA is restricted to being in the form of TLVs and
sub-TLVs, some of which are mandatory and some of which are
positionally dependent in the TLV sequence for proper
interpretation. Opaque LSAs are also restrictive when the flooding
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scope for the content is required to be different from the scope
of the opaque LSA itself.
4.6. Unified for packet and non-packet networks
OSPF-TE is usable within a packet network or a non-packet
network or a combination peer network.
Signaling protocols such as RSVP and LDP work the same across
packet and non-packet networks. Signaling protocols merely need
the TE characteristics of nodes and links so they can signal the
nodes to formulate TE circuit paths. In a peer network, the
underlying control protocol must be capable of providing a
unified LSDB for all TE nodes (nodes with packet-TE links as well
as non-packet-TE links) in the network. OSPF-TE meets this
requirement.
[OPQLSA-TE] is limited in scope for packet networks. An
independent [OPQLSA-GMPLS] is required to support GMPLS links in
a non-packet network. Neither of the Opaque LSA based extensions
have provision to distinguish between node types.
4.7. Networks benefiting from the OSPF-TE design
Many real-world networks are better served by the new-TE-LSAs
scheme. Here are a few examples.
4.7.1. IP providers transitioning to provide 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.
The native OSPF-LSDB will remain undisturbed while newer TE
links are added to the network.
4.7.2. 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.
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4.7.3. Large TE networks
The OSPF-TE design is advantageous in large TE networks that
require the AS to be sub-divided into multiple areas.
4.7.4. Non-packet networks and Peer networks
OSPF-TE is also the right choice for vendors opting for a
stable, well-founded protocol for their non-IP TE networks.
OSPF-TE is uniquely qualified to support the following network
attachments in non-Packet TE networks.
(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).
5. OSPF-TE solution overview
5.1. OSPF-TE Solution
A new TE flag is introduced within the OSPF options field to
to enable discovery of TE topology. Section 8.0 describes the
semantics of the TE flag. TE LSAs are designed for use by the
OSPF-TE nodes. Section 9.0 describes the TE LSAs in detail.
Changes required of the OSPF data structures to support
OSPF-TE are described in section 11.0. A new TE-neighbors data
structure will be used to flood TE LSAs along TE-topology.
An OSPF-TE node will have the native LSDB and the TE-LSDB,
A native OSPF node will have just the native LSDB.
Consider the following OSPF area constituted of OSPF-TE and
native OSPF routers. Nodes RT1, RT2, RT3 and RT6 are OSPF-TE
routers with TE and non-TE link attachments. Nodes RT4 and RT5
are native OSPF routers with no TE links. When the LSA database
is synchronized, all nodes will share the same native LSDB
OSPF-TE nodes alone will have the additional TE-LSDB.
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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
5.2. Assumptions
OSPF-TE is an extension to the native OSPF protocol and does not
mandate changes to the existing OSPF. OSPF-TE design makes the
following assumptions.
1. An OSPF-TE node will need to establish router adjacency with
at least one other OSPF-TE node in the area in order for the
router's TE-database to be synchronized within the area.
Failing this, the OSPF router will not be in the TE
calculations of other TE routers in the area.
It is the responsibility of the network administrator(s) to
ensure connectedness of the TE network. Otherwise, there can
be disjoint TE topologies within a network.
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2. OSPF-TE nodes must advertise the link state of its TE-links.
TE-links are not obligated to support native IP traffic.
Hence, an OSPF-TE node cannot be required to synchronize
its link-state database with neighbors on all its links.
The only requirement is to have the TE LSDB synchronized
across all OSPF-TE nodes in the area. Refer [FLOOD-OPT] for
flooding optimizations.
3. A link in a packet network may be designated as a TE-link or
a native-IP link or both. For example, a link may be used for
both TE and non-TE traffic, so long as the link is
under-subscribed in bandwidth for TE traffic - say, 50% of
the link capacity is set aside for TE traffic.
4. Non-packet TE sub-topologies MUST have a minimum of one node
running OSPF-TE protocol. For example, a SONET/SDH TDM ring
must have a minimum of one Gateway Network Element(GNE)
running OSPF-TE. The OSPF-TE node will advertise on behalf
of all the in the ring.
6. Opaque LSAs to OSPF-TE transition strategy
Below is a strategy to transition implementations using opaque
LSAs to adapt the OSPF-TE 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 topologies
area-wise. By doing this, the TE topology for the AS will
be available at area level abstraction.
3. Use TE-Summary LSAs and TE-AS-external-LSAs for inter-area
Communication. Make use of the TE-topology within an 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 within their
connected areas.
7. OSPF-TE router adjacency - TE topology discovery
OSPF creates adjacencies between neighboring routers for the purpose
of exchanging routing information. In the following subsections, we
describe modifications to the OSPF options field and the use of
Hello protocol to establish TE capability compliance between
neighboring routers in an area. The capability is used as the basis
to build TE topology.
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7.1. The OSPF Options field
A new TE flag is introduced within the options field by this draft
to identify TE extensions to the OSPF. This bit will be used to
distinguish routers that support OSPF-TE. 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 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 the
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 will use the TE-bit to
establish OSPF-TE adjacency. 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 deemed
necessary to leave this bit as is, the OPAQUE-9 LSA (local scope)
can be used on each interface to communicate the support for
OSPF-TE.
7.2. The Hello Protocol
The Hello Protocol is primarily responsible for dynamically
establishing and maintaining neighbor adjacencies. In a TE network,
it is not required for all links and neighbors to establish
adjacency using this protocol. The Hello protocol will use the
TE-bit to establish traffic engineering capability between two
OSPF routers.
For NBMA and broadcast networks, this protocol is responsible for
electing the Designated Router and the Backup Designated Router.
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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.
If deemed necessary to leave the TE-bit unused in the options
field, the OSPF-TE routers could use OPAQUE-9 LSA (local scope)
to communicate TE capability between two OSPF routers.
7.3. The Designated Router
The Designated Router is elected by the Hello Protocol on broadcast
and NBMA networks. In general, when a router's non-TE link first
becomes functional, it checks to see whether there is currently a
Designated Router for the network. If there is one, 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.
TE-compliance (I.e., OSPF-TE) must be implemented on the most robust
routers, as they become likely candidates to take on the 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).
7.4. 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 electing
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).
7.5. Flooding and the Synchronization of Databases
In OSPF, adjacent routers within an area must synchronize their
databases. However, as observed in [FLOOD-OPT], a more concise
requirement of OSPF is that all routers in an area must converge
on the same link state database. It is sufficient to send a
single copy of the LSAs to the neighboring routers in an area
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than send one copy on each connected interface. [FLOOD-OPT]
describes in detail how to minimize flooding (Initial LSDB
synchronization as well as the asynchronous LSA updates) within
an area.
In the case where some of the neighbors are TE compliant and
others are not, the designated OSPF-TE router will exchange
different sets of LSAs with its neighbors. TE LSAs are
exchanged only with the TE neighbors. Native LSAs are
exchanged with all neighbors (TE and non-TE alike).
A new OSPFIGP-TE multicast address 224.0.0.24 may be used for
the exchange of TE compliant database descriptors. Flooding
optimization in a TE network is essential as the control
traffic for a TE network is likely to be higher than that of a
non-TE network. Flooding optimization will help minimize LSA
announcements and the associated retransmissions and
acknowledgements on the network.
7.6. The graph of adjacencies
If two routers have multiple networks in common, they may have
multiple adjacencies between them. The adjacency may be one of
two types - native OSPF adjacency and TE adjacency. OSPF-TE
routers will form both types of adjacency.
Two types of adjacency graphs are possible depending on whether
a Designated Router is elected for the network. On physical
point-to-point networks, Point-to-Multipoint networks and
Virtual links, neighboring routers become adjacent whenever they
can communicate directly. The adjacency can be one of
(a) TE-compliant or (b) native. In contrast, on broadcast and
NBMA networks the designated router and the backup designated
router may maintain two sets of adjacency. The remaining routers
will form either TE-compliant or native adjacency. In the
Broadcast network below, routers RT7 and RT3 are chosen as the
designated and backup routers respectively. Routers RT3, RT4
and RT7 are TE-compliant. RT5 and RT6 are not. So, RT4 will
have TE and native adjacencies with the designated and backup
routers. RT5 and RT6 will only have native adjacency with the
designated and backup routers.
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+---+ +---+
|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.
8. TE LSAs - Packet network
The OSPFv2 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.
LSA types 9 through 11 are defined in [OPAQUE].
Each LSA type has a unique flooding scope. Opaque LSA types
9 through 11 are general purpose LSAs, with flooding
scope set to link-local, area-local and AS-wide (except stub
areas) respectively.
In the following subsections, we define new LSAs for traffic
engineering (TE) use. The Values for the new TE LSA types are
assigned such that the high bit of the LSA-type octet is set
to 1. The new TE LSAs are largely modeled after the existing
LSAs for content format and have a unique flooding scope.
TE-router LSA is defined to advertise TE characteristics of
an OSPF-TE router and all the TE-links attached to the
router. TE-incremental-Link-Update LSA is defined to
advertise incremental updates to the metrics of a TE link.
Flooding scope for both these LSAs is restricted to the
TE nodes in the area.
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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.
TE-AS-external LSA and TE-Circuit-Path LSA are defined to
advertise AS external network reachability and pre-engineered
TE circuits respectively. While flooding scope for both these
LSAs can be the entire AS, flooding scope for the
pre-engineered TE circuit LSA may optionally be restricted to
just the TE topology within an area.
8.1. TE-Router LSA (0x81)
The TE-router LSA (0x81) is modeled after the router LSA and has the
same flooding scope as the router-LSA. However, the scope is
restricted to only the OSPF-TE 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 described in the following sub-sections.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| .... | # 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
Option
In TE-capable router nodes, the TE-bit may be set to 1.
8.1.1. Router-TE flags - TE capabilities of the router
The following flags are used to describe the TE capabilities of an
OSPF-TE router. The remaining bits of the 32-bit word are reserved
for future use.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L|L|P| | | | |L|S|C|
|S|E|S| | | | |S|I|S|
|R|R|C| | | | |P|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
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Indicates the node is Packet Switch Capable.
Bit LSP
MPLS Label switch TLV TE-NODE-TLV-MPLS-SWITCHING follows.
This is applicable only when the PSC flag is set.
Bit SIG
MPLS Signaling protocol support TLV
TE-NODE-TLV-MPLS-SIG-PROTOCOLS follows.
BIT CSPF
CSPF algorithm support TLV TE-NODE-TLV-CSPF-ALG follows.
8.1.2. Router-TE TLVs
The following Router-TE TLVs are defined.
8.1.2.4. TE-NODE-TLV-MPLS-SWITCHING
MPLS switching TLV is applicable only for packet switched nodes. The
TLV specifies the MPLS packet switching capabilities of the TE
node.
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 = 0x8001 | Length = 6 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label depth | QOS | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
'Label depth' is the depth of label stack the node is capable of
processing on its ingress interfaces. An octet is used to represent
label depth. A default value of 1 is assumed when the TLV is not
listed.
'QOS' is a single octet field that may be assigned '1' or '0'. Nodes
supporting QOS are able to interpret the EXP bits in the MPLS header
to prioritize multiple classes of traffic through the same LSP.
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8.1.2.2. TE-NODE-TLV-MPLS-SIG-PROTOCOLS
MPLS signaling protocols TLV lists all the signaling protocol
supported by the node. An octet is used to list each signaling
protocol supported.
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 = 0x8002 | Length = 5, 6 or 7 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol-1 | ... | .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
RSVP-TE protocol is represented as 1, CR-LDP as 2 and LDP as 3.
These are the only permitted signaling protocols at this time.
8.1.2.3. TE-NODE-TLV-CSPF-ALGORITHMS
The CSPF algorithms TLV lists all the CSPF algorithm codes
supported. Support for CSPF algorithms makes the node eligible to
compute complete or partial circuit paths. Support for CSPF
algorithms can also be beneficial in knowing whether or not a node
is capable of expanding loose routes (in an MPLS signaling request)
into a detailed circuit path.
Two octets are used to list each CSPF algorithm code. The algorithm
codes may be vendor defined and unique within an Autonomous System.
If the node supports 'n' CSPF algorithms, the Length would be
(4 + 4 * ((n+1)/2)) octets.
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 = 0x8003 | Length = 4(1 + (n+1)/2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CSPF-1 | .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CSPF-n | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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8.1.3. Link-TE flags - TE capabilities of a link
The following flags are used to describe the TE capabilities of a
link. The remaining bits of the 32-bit word are reserved for
future use.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|T|N|P| | | |D| |S|L|B|C|
|E|T|K| | | |B| |R|U|W|O|
| |E|T| | | |S| |L|G| |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 IP
packet processing.
DBS - Indicates whether or not Database synchronization
is permitted on this link.
SRLG Bit - Shared Risk Link Group TLV TE-LINK-TLV-SRLG follows.
LUG bit - Link usage cost metric TLV TE-LINK-TLV-LUG follows.
BW bit - Link bandwidth TLV TE-LINK-TLV-BANDWIDTH follows.
COL bit - Link Color TLV TE-LINK-TLV-COLOR follows.
8.1.4. Link-TE TLVs
8.1.4.1. TE-LINK-TLV-SRLG
The SRLG describes the list of Shared Risk Link Groups (SRLG) the
link belongs to. Two octets are used to list each SRLG. If the link
belongs to 'n' SRLGs, the Length would be (4 + 4 * ((n+1)/2)) octets.
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 = 0x0001 | Length = 4(1 + (n+1)/2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| SRLG-1 | .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRLG-n | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
8.1.4.2. TE-LINK-TLV-BANDWIDTH
The bandwidth TLV specifies maximum bandwidth, bandwidth available
for TE use and reserved bandwidth as follows.
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 = 0x0002 | Length = 16 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maximum Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth available for TE use |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Bandwidth is expressed in units of 32 bytes/sec (256 bits/sec).
A 32-bit field for bandwidth would permit specification not exceeding
1 tera-bits/sec.
'Maximum bandwidth' is be the maximum link capacity expressed in
bandwidth units.
'Bandwidth available for TE use' is the maximum reservable bandwidth
on the link for use by all the TE circuit paths traversing the link.
The link is oversubscribed when this field is more than the
'Maximum Bandwidth'. When the field is less than the
'Maximum Bandwidth', the remaining bandwidth on the link may likely
be used for non-TE traffic.
'Reserved Bandwidth' is the bandwidth that is currently subscribed
from of the link. 'Reserved Bandwidth' must be less than the
'Bandwidth available for TE use'. New TE circuit paths are able to
claim no more than the difference between the two bandwidths for
reservation.
8.1.4.3. TE-LINK-TLV-LUG
The link usage cost TLV specifies Bandwidth unit usage cost,
TE circuit set-up cost, and any time constraints for setup and
teardown of TE circuits on the link.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0003 | Length = 28 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth unit usage cost |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TE circuit set-up cost |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TE circuit set-up time constraint |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TE circuit tear-down time constraint |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Circuit Setup time constraint
This 64-bit number specifies the time at or after which a
TE-circuit path may be set up on the link. The set-up time
constraint is specified as the number of seconds from the start
of January 1, 1970 UTC. A reserved value of 0 implies no circuit
setup time constraint.
Circuit Teardown time constraint
This 64-bit number specifies the time at or before which all
TE-circuit paths using the link must be torn down. The teardown
time constraint is specified as the number of seconds from the
start of January 1 1970 UTC. A reserved value of 0 implies no
circuit teardown time constraint.
No. of TE Circuit paths
This specifies the number of pre-engineered TE circuit paths
between the advertising router and the router specified in the
link state ID.
8.1.4.4. TE-LINK-TLV-COLOR
The color TLV is similar to the SRLG TLV, in that an Autonomous
System may choose to issue colors to a TE-link meeting certain
criteria. The color TLV can be used to specify one or more colors
assigned to the link as follows. Two octets are used to list each
color. If the link belongs to 'n' number of colors, the Length
would be (4 + 4 * ((n+1)/2)) octets.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x0004 | Length = 4(1 + (n+1)/2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color-1 | .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color-n | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
8.2. TE-incremental-link-Update LSA (0x8d)
A significant difference between a non-TE OSPF network and a TE OSPF
network is that the latter may be subject to frequent real-time
circuit pinning and is likely to undergo TE-state updates. Some
links might undergo changes more frequently than others. Flooding
the network with TE-router LSAs at the aggregated speed of all
link metric changes is simply not desirable. A smaller in size,
TE-incremental-link-update LSA is designed to advertise only the
incremental link updates.
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.
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 |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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
new TE-router LSA update with a larger sequence number is advertised,
the newer sequence number is assumed by al the link LSAs.
8.3. TE-Circuit-path LSA (0x8C)
TE-Circuit-path LSA may be used to advertise the availability of
pre-engineered 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| 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 Duration 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
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
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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 pre-engineered 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 set up. This field is specified only when the
S-bit is set in the TE-circuit-path flags. The set-up time is
specified as the number of seconds from the start of January
1 1970 UTC.
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 specifies the number of pre-engineered TE circuit paths
between the advertising router and the router specified in the
link state ID.
Circuit-TE ID
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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.
8.4. 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 befitting the
external areas are advertised.
8.4.1. 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
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.
For example, a TE-summary network LSA will not summarize a
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network whose links do not fall under an SRLG (Shared-Risk Link
Group). This way, the TE-summary LSA merely advertises the
reachability of TE networks within an area. The specific circuit
paths can be computed by the BDRs. Pre-engineered circuit paths
are advertised using TE-Circuit-path LSA (refer section 8.3).
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
8.4.2. 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
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 |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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, the
Area-ID lists all the areas the ABR belongs to. In the case
the link state ID is an ASBR, the Area-ID 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.
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.
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8.5. 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. TE-AS-external LSAs are
originated by AS boundary routers with TE extensions, and describe
the TE networks and pre-engineered circuit paths external to the
AS. As with AS-external LSA, the flooding scope of the
TE-AS-external LSA is 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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
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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-engineered 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. TE LSAs - Non-packet network
A non-packet network would use all the TE LSAs described in the
previous section for a packet network, albeit with some variations.
These variations are described in the following subsections.
TE-Router-Proxy LSA is defined to allow proxy advertisement for
non-packet TE-nodes by an OSPF-TE router.
9.1. TE-Router LSA (0x81)
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.
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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 the case
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.
9.1.1. Router-TE flags - TE capabilities of the router
Flags specific to non-packet TE-nodes are described below.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|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 TDM
Indicates the node is TDM circuit switch capable.
Bit LSC
Indicates the node is Lambda switch Capable.
Bit FSC
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Indicates the node is Fiber (can also be a non-fiber link
type) switch capable.
9.1.2. 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 ->|
TDM, LSC, FSC bits
- Same as defined for router TE options.
9.2. 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
propagating the TDM network LSA.
9.2.1. 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 is required for SONET RING. Unlike the broadcast
type, the sequence in which the Network Elements (NEs) are
placed on a RING-network is pertinent. The nodes in the ring
must be described clock wise, assuming the Gateway Network
Element (GNE) as the starting element.
9.3. 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
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | 0 | Link-TE options |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link-TE flags | Zero or more Link-TE TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
10. Abstract topology representation with TE support
Below, we consider a TE network composed of three OSPF areas -
Area-1, Area-2 and Area-3, attached together through the backbone
area. Area-1 an has a single area border router, ABR-A1 and no
ASBRs. Area-2 has an area border router ABR-A2 and an AS border
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router ASBR-S1. Area-3 has two area border routers ABR-A2 and
ABR-A3 and an AS border router ASBR-S2. The following network
also assumes a pre-engineered TE circuit path between ABR-A1
and ABR-A2; between ABR-A1 and ABR-A3; between ABR-A2 and
ASBR-S1; and between ABR-A3 and ASBR-S2.
The following figure is an inter-area topology abstraction
from the perspective of routers in Area-1. The abstraction
illustrates reachability of TE networks and nodes within area
to the external areas in the same AS and to the external ASes.
The abstraction also illustrates pre-engineered TE circuit
paths advertised by ABRs and ASBRs.
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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 sets of Neighbors
Two sets of neighbor data structures are required. 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 are 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 may 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 IP
packets. For FSC and LSC TE networks, this flag is set to
FALSE.
IpTerminated
If the value of the flag is TRUE, the interface processes IP
Packet data and hence may be used for 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 IpTerminated 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 though 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
This document proposes that TE LSA types and TE TLVs be
maintained by the IANA. The document also proposes an OSPFIGP-TE
multicast address be assigned by the IANA for the exchange of
TE database descriptors.
OSPFIGP-TE multicast address is suggested a value of 224.0.0.24
so as not to conflict with the recognized multicast address
definitions, as defined in
http://www.iana.org/assignments/multicast-addresses
The following sub-section explains the criteria to be used by the
IANA to assign TE LSA types and TE TLVs.
12.1. TE LSA type values
LSA type is an 8-bit field required by each LSA. TE LSA types
will have the high bit set to 1. TE LSAs can range from 0x80
through 0xFF. The following values are defined in sections
8.0 and 9.0. The remaining values are available for assignment
by the IANA with IETF Consensus [Ref 11].
TE LSA Type Value
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_________________________________________
TE-Router LSA 0x81
TE-Summary Network LSA 0x83
TE-Summary router LSA 0x84
TE-AS-external LSAs 0x85
TE-Circuit-paths LSA 0x8C
TE-incremental-link-Update LSA 0x8d
TE-Router-Proxy LSA 0x8e
12.2. TE TLV tag values
TLV type is a 16-bit field required by each TE TLV. TLV type
shall be unique across the router and link TLVs. A TLV type
can range from 0x0001 through 0xFFFF. TLV type 0 is reserved
and unassigned. The following TLV types are defined in sections
8.0 and 9.0. The remaining values are available for assignment
by the IANA with IETF Consensus [Ref 11].
TE TLV Tag Reference Value
Section
_________________________________________________________
TE-LINK-TLV-SRLG Section 8.1.4.1 0x0001
TE-LINK-TLV-BWA Section 8.1.4.2 0x0002
TE-LINK-TLV-LUG Section 8.1.4.3 0x0003
TE-LINK-TLV-COLOR Section 8.1.4.4 0x0004
TE-NODE-TLV-MPLS-SWITCHING Section 8.1.2.1 0x8001
TE-NODE-TLV-MPLS-SIG-PROTOCOLS Section 8.1.2.2 0x8002
TE-NODE-TLV-CSPF-ALG Section 8.1.2.3 0x8003
13. Acknowledgements
The authors wish to specially thank Chitti Babu and his team
for verifying portions of the specification for a packet
network. The authors also wish to thank Vishwas Manral, Riyad
Hartani and Tricci So for their valuable comments and feedback
on the draft.
14. Security Considerations
Security considerations for the base OSPF protocol are covered
in [OSPF-v2] and [SEC-OSPF]. This memo does not create any new
security issues for the OSPF protocol. Security measures
applied to the native OSPF (refer [SEC-OSPF]) are directly
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applicable to the TE LSAs described in the document. Discussed
below are the security considerations in processing TE LSAs.
Secure communication between OSPF-TE nodes has a number of
components. Authorization, authentication, integrity and
confidentiality. Authorization refers to whether a particular
OSPF-TE node is authorized to receive or propagate the TE LSAs
to its neighbors. Failing the authorization process might
indicate a resource theft attempt or unauthorized resource
advertisement. In either case, the OSPF-TE nodes should take
proper measures to audit/log such attempts so as to alert the
administrator to take necessary action. OSPF-TE nodes may refuse
to communicate with the neighboring nodes that fail to prompt
the required credentials.
Authentication refers to confirming the identity of an originator
for the datagrams received from the originator. Lack of strong
credentials for authentication of OSPF-TE LSAs can seriously
jeopardize the TE service rendered by the network. A consequence
of not authenticating a neighbor would be that an attacker could
spoof the identity of a "legitimate" OSPF-TE node and manipulate
the state, and the TE database including the topology and
metrics collected. This could potentially lead to
denial-of-service on the TE network. Another consequence of not
authenticating is that an attacker could pose as OSPF-TE neighbor
and respond in a manner that would divert TE data to the attacker.
Integrity is required to ensure that an OSPF-TE message has not
been accidentally or maliciously altered or destroyed. The result
of a lack of data integrity enforcement in an untrusted environment
could be that an imposter will alter the messages sent by a
legitimate adjacent neighbor and bring the OSPF-TE on a node and
the whole network to a halt or cause a denial of service for the
TE circuit paths effected by the alteration.
Confidentiality of MIDCOM messages ensure that the TE LSAs are
accessible only to the authorized entities. When OSPF-TE is
deployed in an untrusted environment, lack of confidentiality will
allow an intruder to perform traffic flow analysis and snoop the
TE control network to monitor the traffic metrics and the rate at
which circuit paths are being setup and torn-down. The intruder
could cannibalize a lesser secure OSPF-TE node and destroy or
compromise the state and TE-LDSB on the node. Needless to say, the
least secure OSPF-TE will become the achilles heel and make the TE
network vulnerable to security attacks.
15. Normative References
Srisuresh & Joseph [Page 43]
Internet-Draft OSPF TE extensions December 2002
[IETF-STD] Bradner, S., "Key words for use in RFCs to indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 1700] J. Reynolds and J. Postel, "Assigned Numbers",
RFC 1700
[RFC 2434] Narten, T. and H. Alvestrand, "Guidelines for
writing an IANA Considerations Section in RFCs",
BCP 26, RFC 2434, October 1998.
[MPLS-TE] Awduche, D., et al, "Requirements for Traffic
Engineering Over MPLS," RFC 2702, September 1999.
[OSPF-v2] Moy, J., "OSPF Version 2", RFC 2328, April 1998.
[SEC-OSPF] Murphy, S., Badger, M., and B. Wellington, "OSPF with
Digital Signatures", RFC 2154, June 1997
[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>
15. Informative References
[GMPLS-TE] P.A. Smith et. al, "Generalized MPLS - Signaling
Functional Description", work in progress,
draft-ietf-mpls-generalized-signaling-09.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.
[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-11.txt, Work in
Progress.
[OPAQUE] Coltun, R., "The OSPF Opaque LSA Option," RFC 2370,
July 1998.
Srisuresh & Joseph [Page 44]
Internet-Draft OSPF TE extensions December 2002
[OPQLSA-TE] Katz, D., D. Yeung and K. Kompella, "Traffic
Engineering Extensions to OSPF", work in progress,
<draft-katz-yeung-ospf-traffic-09.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-09.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 45]