Configuring RSVP Automatic Mesh

BGP and MPLS VPNs are based on a peer model. To add a new site to an existing VPN, you need to configure the CE router at the new site and the PE router connected to the CE router. You do not have to modify the configuration of all of the other PE routers participating in the VPN. The PE routers automatically learn about the routes associated with the new site (a process called automatic discovery).

The requirements are a bit different if you need to add a new PE router (as opposed to a CE router) to the network. A BGP and MPLS VPN requires that the BGP session be fully meshed and that there also be a full mesh of PE router-to-PE router MPLS LSPs between all of the PE routers in the network. When you add a new PE router to the network, all of the existing PE routers must be reconfigured to peer with the new PE router. Much of the configuration effort can be reduced if you configure BGP route reflectors (mitigating the full mesh requirement for BGP) and if you configure LDP as the signaling protocol for MPLS.

However, if you need to add a new PE router to a network configured with a full mesh of RSVP-signaled LSPs, you need to reconfigure each of the PE routers to have a peer relationship with the new PE router. You can configure RSVP automatic mesh to address this particular operational scenario. When you enable RSVP automatic mesh, RSVP LSPs are dynamically created between a new PE router and the existing PE routers, eliminating the need to reconfigure all of the PE routers manually. For dynamic tunnel creation to function properly, BGP must be configured to exchange routes between all of the participating PE routers. If two BGP peers did not exchange routes, it would not be possible to configure a dynamic tunnel between them.

RSVP includes numerous capabilities that are not available in LDP, including fast reroute. RSVP automatic mesh helps to reduce the operation and maintenance requirements for RSVP, making it possible to deploy RSVP in larger and more complicated networks.

Every PE router can reach every other PE router in the network because this information is distributed by the IGP. A PE router can set up an RSVP LSP to any other PE router in the network so long as it knows that such an LSP is required. To build a full mesh of LSPs between the PE routers requires that each PE router know which of the other PE routers make up the full mesh.

Since the IGP distributes reachability information to all PE routers and already carries traffic engineering information, it can also distribute mesh group membership information. OSPF and IS-IS can transmit the traffic engineering mesh group type length values (TLVs), indicating what group or groups the PE router belongs to and the address that should be used by other PE routers for establishing an LSP toward it. Based on the advertisements received and the locally configured mesh information, each PE router knows which other PE routers it can dynamically establish LSPs to.

You can configure RSVP to establish LSPs automatically for any new PE router added to a full mesh of LSPs. To enable this feature, you must configure the rsvp-te statement on all of the PE routers in the full mesh.

Note: You cannot configure RSVP automatic mesh in conjunction with CCC. CCC cannot use the dynamically generated tunnels.

You can configure these statements at the following hierarchy levels:

• [edit routing-options dynamic-tunnels tunnel-name]
• [edit logical-systems logical-system-name routing-options dynamic-tunnels tunnel-name]

You can configure the following optional statements for RSVP automatic mesh:

• destination-networks—Specify the IP version 4 (IPv4) prefix range for the destination network. Dynamic tunnels within the specified IPv4 prefix range are allowed to be initiated.
• label-switched-path-template—You can configure either the default template explicitly using the default-template option or you can configure an LSP template of your own using the template-name option. The LSP template acts as a model configuration for all of the dynamically generated LSPs.