H3C Technologies H3C S7500E Series Switches - Manual (Page 92)

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For more information about static routing, see Static Routing Configuration in the Layer 3 - IP Routing
Configuration Guide .
Automatic route advertisement
You can use automatic route advertisement to advertise MPLS TE tunnel interface routes to IGPs,
allowing traffic to be routed down MPLS TE tunnels.
Two approaches are available to automatic route advertisement: IGP shortcut and forwarding
adjacency.
OSPF and IS-IS support both approaches where TE tunnels are considered point-to-point links and
TE tunnel interfaces can be set as outgoing interfaces.
IGP shortcut, also known as autoroute announce, considers a TE tunnel as a logical interface directly
connected to the destination when computing IGP routes on the ingress of the TE tunnel.
IGP shortcut and forwarding adjacency are different in that in the forwarding adjacency approach,
routes with TE tunnel interfaces as outgoing interfaces are advertised to neighboring devices but not
in the IGP shortcut approach. Therefore, TE tunnels are visible to other devices in the forwarding
adjacency approach but not in the IGP shortcut approach.
Figure 3-3 IGP shortcut and forwarding adjacency
Router D
Router A
Router B
Router C
Router E
10
20
10
10
10
20
As shown in Figure 3-3 , 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.