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Operation Manual – MPLS TE
H3C S9500 Series Routing Switches
Chapter 1 MPLS TE Configuration
1-12
Router D
Router A
Router B
Router C
Router E
10
20
10
10
10
20
Figure 1-3
IGP shortcut and forwarding adjacency
As shown in
Figure 1-3
, 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
known the presence of the TE tunnel and thus 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:
z
The tunnel destination address should be in the same area where the tunnel
interface is located.
z
The tunnel destination address should be reachable through intra-area routing.
1.1.8 CR-LSP Backup
CR-LSP backup provides end-to-end path protection for the entire LSP without time
limitation. This is different from fast reroute (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.
Two approaches are available CR-LSP backup:
z
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.
z
Standard backup where a secondary CR-LSP is created to take over after the
primary CR-LSP fails.