Supported Platforms
RSVP and IGP Hello Packets and Timers
RSVP monitors the status of the interior gateway protocol (IGP) (IS-IS or OSPF) neighbors and relies on the IGP protocols to detect when a node fails. If an IGP protocol declares a neighbor down (because hello packets are no longer being received), RSVP also brings down that neighbor. However, the IGP protocols and RSVP still act independently when bringing a neighbor up.
In the Junos OS, RSVP typically relies on IGP hello packet detection to check for node failures. RSVP sessions are kept up even if RSVP hello packets are no longer being received, so long as the router continues to receive IGP hello packets. RSVP sessions are maintained until either the router stops receiving IGP hello packets or the RSVP Path and Resv messages time out. Configuring a short time for the IS-IS or OSPF hello timers allows these protocols to detect node failures quickly.
RSVP hellos can be relied on when the IGP does not recognize a particular neighbor (for example, if IGP is not enabled on the interface) or if the IGP is RIP (not IS-IS or OSPF). Also, the equipment of other vendors might be configured to monitor RSVP sessions based on RSVP hello packets. This equipment might also take an RSVP session down due to a loss of RSVP hello packets.
We do not recommend configuring a short RSVP hello timer. If quick discovery of a failed neighbor is needed, configure short IGP (OSPF or IS-IS) hello timers.
OSPF and IS-IS have infrastructure to manage rapid hello message sending and receiving reliably, even if the routing protocols or some other process are straining the processing capability of the router. Under the same circumstances, RSVP hellos might time out prematurely even though the neighbor is functioning normally.
