Graceful handling of resource exhaustion enhances the behavior of LDP when a data path or a CSM resource required for the resolution of a FEC is exhausted. In prior releases, the entire LDP protocol was shut down, causing all LDP peering sessions to be torn down and therefore impacting all peers. The user was required to fix the issue that caused the FEC scaling to be exceeded, and to restart the LDP session by executing the no shutdown CLI command. With graceful handling of resource exhaustion, only the responsible session or sessions are shut down, which impacts only the appropriate peer or peers.
Graceful handling of resources implements a capability by which the LDP interface to the peer, or the targeted peer in the case of a targeted LDP (T-LDP) session, is shut down.
If LDP tries to resolve a FEC over a link or a T-LDP session and runs out of data path or CSM resources, LDP brings down that interface or targeted peer, which brings down the Hello adjacency over that interface to all linked LDP peers or to the targeted peer. The interface is brought down for the LDP context only and is still available to other applications such as IP forwarding and RSVP LSP forwarding.
After taking action to free up resources, the user must manually perform a no shutdown command on the interface or the targeted peer to bring it back into operation. This re-establishes the Hello adjacency and resumes the resolution of FECs over the interface or to the targeted peer.