# Configuring RSVP-TE Hello Messages to Determine Peer Reachability

The RSVP-TE hello feature enables RSVP-TE peers to exchange hello messages and establish a hello adjacency. The peers use the adjacency to verify reachability. When a peer is no longer reachable, the LSPs that traverse the neighbor are torn down.

High refresh values reduce the amount of control traffic (and CPU cycles) needed by RSVP-TE to refresh LSP state across the network, reducing the impact of RSVP-TE on system resources:

- A hello refresh interval of 1000 milliseconds (a rate of one hello every second) is appropriate for a small configuration—tens of interfaces—without causing performance degradation.
- For larger configurations, the default hello refresh interval of 10,000 milliseconds (a rate of one hello every 10 seconds) is more appropriate and typically does not cause performance degradation.

To configure the RSVP-TE hello feature on all RSVP-TE interfaces in the VR:

1. Issue the mpls rsvp signalling hello command.
   host1:vr5(config)#mpls rsvp signalling hello
2. (Optional) Configure the refresh interval.
   host1(config-if)#mpls rsvp signalling hello refresh interval 5000
3. (Optional) Configure the refresh misses.
   host1(config-if)#mpls rsvp signalling hello refresh misses 5

To configure the RSVP-TE hello feature on a RSVP-TE specific interface:

1. Access the interface.
   host1(config)#interface fastEthernet 4/3
2. Issue the mpls rsvp signalling hello command.
   host1(config-if)#mpls rsvp signalling hello
3. (Optional) Configure the refresh interval.
   host1(config-if)#mpls rsvp signalling hello refresh interval 5000
4. (Optional) Configure the refresh misses.
   host1(config-if)#mpls rsvp signalling hello refresh misses 5

   | Note: Issuing the refresh interval or the refresh misses keywords only configures the refresh values; this action has no effect on enabling or disabling hellos.

#### Related Documentation

- Basic MPLS Configuration Tasks
- Additional RSVP-TE Configuration Tasks
- mpls rsvp signalling hello