Shared Explicit Style

The Shared Explicit (SE) RSVP style that is used for TE ensures that make-before-break is issued. SE style is advertised in the PATH message, as shown in Example 8-16. This means that when an LSR needs to reroute a TE LSP, the new TE LSP is built before the old TE LSP is torn down for a specific TE tunnel. The traffic is only switched onto the new LSP when it is completely set up to avoid or reduce traffic loss. The bandwidth reserved on the links that might be used by both the old and the new TE LSP for a particular TE tunnel is not accounted for twice: once for the old LSP and once for the new LSP. The same can happen when the administrator increases the required bandwidth of an existing TE tunnel. The old and new bandwidth requirements are not reserved at the same time on shared links; rather, the highest amount of bandwidth is accounted. In Figure 814, one TE tunnel is reoptimizing. While this is happening, the RSVP SE style ensures the absence of bandwidth double booking on the links that are shared between the old and new LSP of this tunnel.

LSP Is Rerouted To More Optimal Path

New Path Of TE LSP

New Path Of TE LSP

Old Path Of TE LSP
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