The SE RSVP reservation style creates shared reservations among explicit senders. For a single RSVP bandwidth reservation, the egress router (receiver) lists the senders sharing the reservation in a Resv message, resulting in the following:
- A multipoint-to-point LSP if the Path message does not contain an ERO or if the ERO is identical across senders. A common label is assigned.
- A separate LSP for each sender if the Path message contains a different ERO for each sender. A different label is assigned to different senders.
- Each LSP shares the bandwidth of the largest request across the shared link.
While any LSP can be established with an SE style reservation, the SE reservation is most useful during LSP reroute, for example, when a standby secondary path or link protection is configured. In general, the secondary LSP inherits the reservation style of the primary LSP, which is FF by default, or SE if link protection is used, unless the secondary LSP is configured with the adaptive statement at the secondary path level. See Figure 9.
The network shown in Figure 9 shows two paths, R1-R2-R4-R5 and R1-R7-R9-R5. The paths are configured as either a strict primary or strict standby secondary path for an adaptive LSP, or as lsp1 and lsp2. Both configurations originate from R1 and share the link between R2 and R4. For more information about adaptive LSPs, see Configuring and Verifying an Adaptive LSP.
If a network problem results in an LSP reroute, the SE reservation style allows a smooth transition from either a primary path to a standby secondary path, or from on old LSP to a new LSP with the make-before-break operation. This style also permits the old and new LSPs to share a single reservation over links they have in common, preventing double counting of resources.