Globally enables the handling of an IGP neighbor down event by MPLS. This command takes effect immediately and you can run it as needed.
By default, RSVP does not handle IGP neighbor down events. RSVP IGP synchronization must be enabled to handle an IGP neighbor down event.
MPLS policy mode (config-router-mpls-policy)
The handle-isis-neighbor-down command is independent of MPLS traffic engineering configurations. The handle-isis-neighbor-down command allows MPLS (RSVP) to handle IGP neighbor down events and take action, such as tearing down the associated RSVP sessions. For example, when IS-IS is configured as MPLS TE protocol, the user can still configure MPLS to handle an OSPF neighbor down event (and vice versa).
An IGP neighbor down event is handled only by the RSVP sub-component of MPLS by tearing down the associated sessions. This event is not handled by LDP sub-component of MPLS.
MPLS RSVP does not keep track of the current state of IGP neighbor. That is, when an IGP neighbor goes down, RSVP tears down all the associated sessions. But RSVP does not prevent bringing up any session while the IGP neighbor to RSVP next-hop is down (or not yet available). That is, the RSVP session is brought up even when the IGP neighbor to the next-hop does not exist.
An IGP neighbor down is treated as upstream neighbor down or downstream neighbor down event by RSVP, depending upon the direction of the LSP. When a downstream IGP neighbor goes down, it results in an LSP tear down or FRR switchover, whichever is applicable.
MPLS receives and processes an IGP neighbor down event only for the cases when an IGP neighbor goes down because of hellos not received from the peer.
When an IGP neighbor goes down because of an underlying interface down, MPLS does not react to an IGP neighbor down event as RSVP would also receive the interface down event and tears down associated LSP sessions. Handling an IGP neighbor down event is redundant in such situations.
When BFD is configured on IGP interfaces, an IGP neighbor down is detected quickly and may help RSVP converge faster.
When an IGP neighbor is Nonstop Routing or Graceful Restart capable, MPLS does not receive a neighbor down event when NSR is performed on the peer IGP router.
Faster FRR feature is not be triggered when MPLS detects that IGP neighbor is down. Instead, each FRR LSP is processed individually to perform local repair.
It is highly recommended to observe extreme caution when implementing this feature when BFD is enabled for the underlying IGP. Under some circumstances, unnecessary flapping for RSVP sessions/LSPs can occur with this combination.
The no version of the command does not handle IGP neighbor down events.
MPLS is supported on the Extreme 8820, SLX 9740, SLX 9640, and SLX 9540 devices only.
The following example shows how to enable the RSVP to handle IGP neighbor down events for IS-IS.
device# configure device(config)# router mpls device(config-router-mpls)# policy device(config-router-mpls-policy)# handle-isis-neighbor-down