If the one-hop option is specified instead of a prefix policy, the auto-lsp command enables the automatic signaling of single-hop, point-to-point LSPs using the specified template to all directly connected neighbors. This LSP type is referred to as auto-created single-hop LSPs of type one-hop. Unlike the automatically created RSVP-TE LSP mesh, the automatically created single-hop RSVP-TE LSPs have no requirement for a prefix list to be referenced.
The first requirement is to create an LSP template containing the common parameters used to establish each single-hop LSP. The template must be created with the keyword one-hop-p2p:
config>router>mpls>lsp-template template-name one-hop-p2p
Upon creation of the template, CSPF is automatically enabled (and cannot be disabled), and the hop-limit is set to a value of two. The hop-limit defines the number of nodes the LSP may traverse, and since these are single-hop LSPs to adjacent neighbors, a limit of two is sufficient. The template must also reference a default path before it can be placed in the no shutdown state.
The next requirement is to trigger the creation of single-hop LSPs using the auto-lsp lsp-template command:
config>router>mpls>auto-lsp lsp-template template-name one-hop
The LSP and path parameters and options supported in an LSP template of type one-hop-p2p are the same as those in the LSP template of type mesh-p2p. The show command for auto-lsp will display the actual outgoing interface address in the ‟from” field.
The auto-created single-hop LSP can be signaled over both numbered and unnumbered RSVP-TE interfaces.
When the one-hop command is executed, the TE database keeps track of each TE link to a directly connected IGP neighbor whose router ID is discovered. MPLS then signals an LSP with a destination address matching the router ID of the neighbor and with a strict hop consisting of the address of the interface used by the TE link. The auto-lsp command with the one-hop option results in one or more LSPs signaled to the IGP neighbor.
Only the router ID of the first IGP instance of the neighbor that advertises a TE link causes the LSP to be signaled. If another IGP instance with a different router ID advertises the same TE link, no action is taken and the existing LSP is kept up. If the router ID originally used disappears from the TE database, the LSP is kept up and is now associated with the other router ID.
The state of a single-hop LSP that is signaled displays the following behavior.
If the interface used by the TE link goes down or BFD times out and the RSVP-TE interface is registered with BFD, the LSP path moves to the bypass backup LSP if the primary path is associated with one.
If the association of the TE link with a router ID is removed from the TE database while the single-hop LSP is up, the single-hop LSP is torn down whether the bypass backup path is activated or not. This occurs if the interface used by the TE link is deleted or if the interface is shut down in the context of RSVP-TE.
If the TE database loses the router ID while the LSP is up, it will perform two separate updates to MPLS, whether the bypass backup path is activated or not. The first one updates the loss of the TE link association, which will cause the single-hop LSP to be torn down. The other update states that the router ID is no longer in the TE database, which will cause MPLS to tear down all mesh LSPs to this router ID. A shutdown at the neighbor of the IGP instance that advertised the router ID will cause the router ID to be removed from the ingress LER node immediately after the last IGP adjacency is lost and not be subject to time-out as it is for a non-directly connected destination router.
All other feature behavior and limitations are the same as for an auto-created LSP mesh.