R3303-HP HSR6800 Routers MPLS Configuration Guide

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Figure 17 IGP shortcut and forwarding adjacency
A TE tunnel is present between Router D and Router C. With IGP shortcut enabled, the ingress node
Router D can use this tunnel when calculating IGP routes. This tunnel, however, is invisible to Router A.
Therefore, Router A cannot use this tunnel to reach Router C. With forwarding adjacency enabled, Router
A can know the presence of the TE tunnel and forward traffic to Router C to Router D though this tunnel.
The configuration of IGP shortcut and forwarding adjacency is broken down into tunnel configuration
and IGP configuration. When making tunnel configuration on a TE tunnel interface, consider the
following:
• The tunnel destination address must be in the same area where the tunnel interface is located.
• The tunnel destination address must be reachable through intra-area routing.
Automatic bandwidth adjustment
Because users cannot estimate accurately how much traffic they need to transmit though service provider
networks, they are more willing to pay for used bandwidth. Therefore, a service provider should be able
to create TE tunnels from CR-LSPs with initially requested bandwidth for users, and automatically tune the
bandwidth resources assigned to these CR-LSPs when user services increase.
Traffic engineering must be capable of dynamically allocating resources without interrupting services
when network environment changes.
Automatic bandwidth adjustment of MPLS TE fulfills this function. It can dynamically tune TE tunnel
bandwidth based on measured service traffic.
CR-LSP backup
CR-LSP backup provides end-to-end path protection for the entire LSP without time limitation. This is
different from FRR, which provides quick but temporary per-link or per-node protection on an LSP.
In the same TE tunnel, the LSP used to back up a primary LSP is called a secondary LSP. When the ingress
of a TE tunnel detects that the primary LSP is unavailable, it switches traffic to the secondary LSP and after
the primary LSP becomes available, switches traffic back. This is how LSP path protection is achieved.
The following methods are available for CR-LSP backup:
• Hot backup where a secondary CR-LSP is created immediately after a primary CR-LSP is created.
MPLS TE switches traffic to the secondary CR-LSP after the primary CR-LSP fails.