Brocade Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide (Supporting R05.6.00) User Manual
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Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide
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OSPF-TE Link State Advertisements for MPLS interfaces
1
CSPF is enabled by default for signaled LSPs, but can be disabled. When signaled LSPs are
configured without CSPF, the shortest path from the ingress LER to the egress LER is calculated
using standard hop-by-hop routing methods. When the LSP also is configured to use a
user-specified path, the device calculates the shortest path between each LSR in the path. As with
CSPF, the output of this process is a fully specified path of physical interfaces on LSRs.
The advantage of configuring signaled LSPs without CSPF is that it can span multiple OSPF areas
or IS-IS levels. Since OSPF-TE LSAs and IS-IS LSPs with TE extensions have area/level flooding
scope, the information in an LSRs TED is relevant only to their area or level. Consequently, signaled
LSPs that use CSPF can span only an OSPF area or IS-IS level. Signaled LSPs that do not use CSPF,
because they do not rely on information in the TED, do not have this restriction.
Once the path for the LSP has been calculated, RSVP signaling then causes resources to be
reserved and labels to be allocated on each LSR specified in the path. This may cause already
existing, lower priority LSPs to be preempted. Once resources are reserved on all the LSRs in the
path, the signaled LSP is considered to be activated; that is, packets can be forwarded over it.
The following sections provide additional information about the individual components of the
process for activating traffic-engineered signaled LSPs, illustrated in
.
OSPF-TE Link State Advertisements for MPLS interfaces
MPLS-enabled devices running OSPF can be configured to send out LSAs that have special
extensions for traffic engineering. These LSAs, called OSPF-TE LSAs, contain information about
interfaces configured for MPLS. The OSPF-TE LSAs are flooded throughout the OSPF area. LSRs
that receive the OSPF-TE LSAs place the traffic engineering information into a TED, which maintains
topology data about the nodes and links in the MPLS domain.
Traffic engineering information is carried in OSPF traffic engineering (OSPF-TE) LSAs. OSPF-TE LSAs
are Type 10 Opaque LSAs, as defined in RFC 2370. Type 10 Opaque LSAs have area flooding
scope.
OSPF-TE LSAs have special extensions that contain information related to traffic engineering; these
extensions are described in RFC 3630. The extensions consist of Type/Length/Value triplets (TLVs)
containing the following information:
•
Type of link (either point-to-point or multiaccess network)
•
ID of the link (for point-to-point links, this is the Router ID of the LSR at the other end of the
link; for multiaccess links, this is the address of the network’s designated router)
•
IP address of the local interface for the link
•
IP address of the remote interface for the link (this could be zero for multicast links)
•
Traffic engineering metric for the link (by default, this is equal to the OSPF link cost)
•
Maximum bandwidth on the interface
•
Maximum reservable bandwidth on the interface
•
Unreserved bandwidth on the interface
•
Administrative groups to which the interface belongs
When configured to do so, the device sends out OSPF-TE LSAs for each of its MPLS-enabled
interfaces. The user can optionally specify the maximum amount of bandwidth that can be
reserved on an interface, as well as assign interfaces to administrative groups. Refer to
traffic engineering parameters for MPLS interfaces”
for more information.