LDP Strict Targeted Hellos

You can use the strict targeted hello messages feature to prevent LDP sessions from being established with remote neighbors that have not been specifically configured. If the strict targeted hellos feature is enabled, an LDP peer does not respond to targeted hello messages coming from a source that is not one of its configured remote neighbors. Configured remote neighbors can include: 

• Endpoints of RSVP tunnels for which LDP tunneling is configured
• Layer 2 circuit neighbors
• Explicit neighbors in the LDP configuration 

If an unconfigured neighbor sends a hello message, the LDP peer ignores the message and logs an error (with the error trace flag) indicating the source. For example, if the LDP peer received a targeted hello from the Internet address 10.0.0.1 and no neighbor with this address is specifically configured, "LDP: Ignoring targeted hello from 10.0.0.1" is logged in the LDP log file. Remote loop-free alternates (remote LFAs) might use targeted LDP sessions, which are established dynamically on-demand without any explicit configuration. Therefore, if the strict targeted hello feature is enabled, remote LFA might not work properly, as dynamically triggered targeted LDP sessions required for remote LFA might be blocked.