Automatic Bandwidth Adjustment - 3Com MSR 50 Series Configuration Manual

Automatic Bandwidth
Adjustment
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 387 IGP shortcut and forwarding adjacency
Router B
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Router A
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Router D
As shown in Figure 387, 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:
The tunnel destination address should be in the same area where the tunnel
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interface is located.
The tunnel destination address should be reachable through intra-area routing.
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As 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 switch engineering thus must be able to dynamically allocate resources
without interrupting services when network environment changes.
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10
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Router E
MPLS TE Overview
Router C
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