Configuring SR-TE on-demand LSPs

About this task

Configure SR-TE on-demand LSPs using the steps in this section.

Procedure

Define a policy statement to import the route, as shown in the following example:

Example

configure>router>policy-options>policy-statement
   
   entry
      from
        family <family>
        next-hop <ip-address>
        community <comm-name>
      action accept 
         admin-tag-policy <admin-tag-policy-name>
         create-mpls-tunnel

Configure the auto-LSP under MPLS with the template type on-demand-p2p-srte.
The create-mpls-tunnel action is supported for the following address families:
- vpn-ipv4
- vpn-ipv6
- evpn
- label-ipv4
- label-ipv6
- ipv4
- ipv6
The router-policy action assigns an admin-tag-policy to the routes that are imported with a specific next hop and match a specified extended community. In most applications, the extended community is the transport color extended community. The create-mpls-tunnel command action causes BGP to send the next hop and the include and exclude constraints in the admin-tag-policy (if one was assigned to a route by the policy statement) to the MPLS application.

When such a policy statement is applied in the context of a specific VRF, the create-mpls-tunnel command trigger is only actioned by BGP on a per-next-hop basis.

This type of LSP template supports PCE computation, control, and the fallback path computation method if the PCE is unreachable. The auto-LSP is configured using the following command:
```
configure>router>mpls
     auto-lsp <on-demand-p2p-srte-template-name>
```
The LSP template may contain an LSP admin-tag-policy. MPLS takes the next hop, and the admin-tag command includes or excludes constraints from BGP and matches them against the auto-LSP statement with a template with an admin-tag command that conforms to the admin-tag-policy constraints.

If BGP does not pass any admin-tag-policy constraints, MPLS only matches against LSP templates that do not have the admin-tag command configured.

If the next-hop and admin-tag-policy match more than one auto-LSP statement, an LSP is created for each matching entry. This results in an ECMP set to the next hop.

Note:
Each LSP may have a different admin-tag value, but it is an ECMP next-hop tunnel from the perspective of the colored route that triggers the tunnel creation.

A new SR-TE LSP is consequently created to the next hop passed by BGP according to the parameters contained in the LSP template.

The router tracks the binding between BGP triggers and on-demand LSPs that are successfully created and deleted toward a specified BGP next-hop matching an admin-tag-policy.