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Figure 26 IGP shortcut and forwarding adjacency diagram
As shown in
only the ingress node Router D to use the MPLS TE tunnel in the IGP route calculation. Router A
cannot use this tunnel to reach Router C. With forwarding adjacency enabled, Router A can also
know the existence of the MPLS TE tunnel. Router A can use this tunnel to transfer traffic to Router C
by forwarding the traffic to Router D.
Make-before-break
Make-before-break is a mechanism to change an MPLS TE tunnel with minimum data loss and
without using extra bandwidth.
In cases of tunnel reoptimization and automatic bandwidth adjustment, traffic forwarding is
interrupted if the existing CRLSP is removed before a new CRLSP is established. The
make-before-break mechanism ensures that the existing CRLSP is removed after the new CRLSP is
established and the traffic is switched to the new CRLSP. However, this wastes bandwidth resources
if some links on the old and new CRLSPs are the same. This is because you need to reserve
bandwidth on these links for the old and new CRLSPs separately. The make-before-break
mechanism uses the SE resource reservation style to address this problem.
The resource reservation style refers to the style in which RSVP-TE reserves bandwidth resources
during CRLSP establishment. The resource reservation style used by an MPLS TE tunnel is
determined by the ingress node, and is advertised to other nodes through RSVP.
The device supports the following resource reservation styles:
•
FF—Fixed-filter, where resources are reserved for individual senders and cannot be shared
among senders on the same session.
•
SE—Shared-explicit, where resources are reserved for senders on the same session and
shared among them. SE is mainly used for make-before-break.
Figure
26, an MPLS TE tunnel exists from Router D to Router C. IGP shortcut enables
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