Multiarea Support - Cisco ASR 9000 Series Configuration Manual

MPLS Traffic Engineering Interarea Tunneling

Multiarea Support

Multiarea support allows an area border router (ABR) LSR to support MPLS-TE in more than one IGP area.
A TE LSP is still confined to a single area.
Multiarea and Interarea TE are required when you run multiple IGP area backbones. The Multiarea and
Interarea TE allows you to:
• Limit the volume of flooded information.
• Reduce the SPF duration.
• Decrease the impact of a link or node failure within an area.
Figure 13: Interlevel (IS-IS) TE Network
As shown in the figure, R2, R3, R7, and R4 maintain two databases for routing and TE information. For
example, R3 has TE topology information related to R2, flooded through Level-1 IS-IS LSPs plus the TE
topology information related to R4, R9, and R7, flooded as Level 2 IS-IS Link State PDUs (LSPs) (plus, its
own IS-IS LSP).
You can configure multiple areas within an IS-IS Level 1. This is transparent to TE. TE has topology
Note
information about the IS-IS level, but not the area ID.
Loose Hop Expansion
Loose hop optimization allows the reoptimization of tunnels spanning multiple areas and solves the problem
which occurs when an MPLS-TE LSP traverses hops that are not in the LSP's headend's OSPF area and IS-IS
level.
Interarea MPLS-TE allows you to configure an interarea traffic engineering (TE) label switched path (LSP)
by specifying a loose source route of ABRs along the path. It is the then the responsibility of the ABR (having
a complete view of both areas) to find a path obeying the TE LSP constraints within the next area to reach
the next hop ABR (as specified on the headend). The same operation is performed by the last ABR connected
to the tailend area to reach the tailend LSR.
For P2MP-TE tunnels, ABRs support loose hop ERO expansion to find path to the next ABR until it reaches
to the tail-end LSR, without introducing remerge.
You must be aware of these considerations when using loose hop optimization:
Cisco ASR 9000 Series Aggregation Services Router MPLS Configuration Guide, Release 4.3.x
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Implementing MPLS Traffic Engineering
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