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Cisco ME 3800X and 3600X Switch Software Configuration Guide
OL-23400-01
Chapter 34 Configuring MPLS, MPLS VPN, MPLS OAM, and EoMPLS
Understanding MPLS Traffic Engineering and Fast Reroute
Paths for LSPs are calculated at the LSP headend, the first router in the LSP path. Under failure
conditions, the headend determines a new route for the LSP based on destination, bandwidth, link
attributes, and priority. RSVP-TE then establishes and maintains the TE tunnel across the MPLS
backbone network. Packets are switched inside the tunnel by using MPLS labels. Recovery at the
headend provides for the optimal use of resources.
The number of supported tunnels depends upon the installed license. Refer to the licensing document.
The switch supports these MPLS TE features:
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OSPF, IS-IS, and RSVP extensions to support MPLS TE
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TE autotunnel primary and backup
•
TE tunnel reoptimization to improve overall efficiency by rerouting some traffic trunks to new paths
•
TE load sharing to a destination over paths with unequal costs. The switch supports up to 256
load-shared routes (load-shared routes for up to 256 destinations). Any additional load-balanced
routes are forwarded in one path in the hardware.
•
TE IP explicit address exclusion to exclude a link or node from the path. You use the ip explicit-path
global configuration mode to enter explicit-path configuration mode and then use the
exclude-address command to specify addresses to exclude from the path.
•
Support for LDP over TE tunnels for Layer 3 VPN traffic by entering the mpls ip interface
configuration command on the tunnel interface. The switch does not support LDP over TE tunnels
for Layer 2 VPN traffic.
•
Traffic forwarding to the TE tunnel using static routing
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TE autoroute, which installs the routers announced by the tailend router and the downstream routers
into the routing table of the headend router. All traffic directed to prefixes beyond the tunnel end are
pushed into the tunnel.
•
Prefix-independent fast reroute.
The switch does not support these MPLS TE features:
•
Interarea TE support for OSPF and IS-IS
•
TE path protection
•
Shared risk link group (SRLG)
•
Traffic forwarding to the TE tunnel using policy routing
•
Traffic forwarding to the TE tunnel using forwarding adjacency
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Auto bandwidth
•
Autotunnel mesh group
MPLS TE Fast Reroute
With MPLS TE, when a link or node failure occurs, the LSP headend determines a new route for the LSP.
However, due to messaging delays, the headend cannot recover as quickly as making a repair at the point
of failure.
Fast reroute (FRR) protects the LSPs from link and node failures by locally repairing the LSP
at the point of failure, allowing data to continue to flow while the headend routers establish replacement
end-to-end LSPs. Fast reroute locally repairs the protected LSP by rerouting all LSP traffic crossing a
failed link over backup tunnels that bypass the failed link or node.
•
Link protection is also referred to as next hop (N-Hop) protection because the new route terminates
at the next hop beyond the LSP failure.
