# RSVP-TE Hellos Based on Node IDs Overview

For interoperability with routers that cannot support RSVP-TE graceful restart with link-based hellos, you can use the mpls rsvp signalling node-hello command to configure the exchange of node-ID–based RSVP-TE hellos (node hellos). E Series routers use node hellos only to support their graceful restart capabilities.

| Note: Node hellos are not required for RSVP-TE graceful restart support between routers running JunosE Software or for interoperability with routers running Junos OS.

Graceful restart must be enabled for node hellos to advertise graceful restart. Link-based hellos are not required for graceful restart when you have configured node hellos. However, you might still use link-based hellos to monitor RSVP-TE links and detect link failures.

The node hello sessions are established by the exchange of hello messages in which node IDs are used for the source and destination addresses in the hello packets. The sending router uses its local node ID as the source address and the remote node ID of the receiving router as the destination address.

RSVP-TE uses the configured IGP, IS-IS or OSPF, to learn the local and remote node IDs. In IS-IS, the node ID is the TE router ID as defined in the traffic engineering router ID TLV for IPv4 addresses and in the IPv6 TE Router_ID for IPv6 addresses. In OSPF, the node ID is the TE router ID as defined in the router address TLV for IPv4 addresses and in the Router_IPv6_Address for IPv6 addresses. Only one node-based RSVP-TE hello session can be established for each instance of an IGP adjacency with a peer.

When a router receives a hello message where the destination address is set to the receiving router’s local node ID, the router verifies that the node ID is the ID that the IGP advertises. This router must then use its local node ID as the source address when it replies to the sending router.

Node-based hellos are an attractive alternative to link-based hellos for graceful restart when you use bidirectional forwarding detection (BFD) for link monitoring and you have configured node-based hellos on all RSVP-TE peers.

Link-based RSVP-TE hellos are used for monitoring RSVP-TE adjacencies with neighboring routers and for providing RSVP-TE graceful restart. However, the BFD protocol is more effective at monitoring RSVP-TE adjacencies than are link-based hellos.

Link-based RSVP-TE hellos for graceful restart are more resource-intensive option than node-based RSVP-TE hellos when your configuration has several interfaces enabled with MPLS RSVP-TE and carrying RSVP-TE data traffic. Link-based hellos generate a volume of network traffic and processing overhead that is directly proportional to the number of interfaces that are carrying active RSVP-TE tunnels.

Node-based hellos require less messaging and processing overhead in these circumstances. Node hellos require only a single hello session between the two node IDs, compared to link-based hellos that have hello sessions between all interface pairs. Less traffic and overhead result in a lesser impact on scaling.

Node-based hellos can therefore be advantageous even when you are interoperating with routers that are running JunosE Software or Junos OS, if you are using BFD to monitor your RSVP-TE links. If you are not using BFD, then you must use link-based hellos for link monitoring, and link-based hellos then become more practical for graceful restart.

#### Related Documentation

- Configuring RSVP-TE Hellos Based on Node IDs