Alcatel-Lucent 7750 SR Manual page 1057

Virtual Private Routed Network Services
The availability of the far-end static route is monitored through periodic polling. The polling
period is configured. If the poll fails a specified number of sequential polls, the static route is
marked as inactive.
Either ICMP ping or unicast ARP mechanism can be used to test the connectivity. ICMP ping is
preferred.
If the connectivity check fails and the static route is de-activated, the SR-Series router will
continue to send polls and re-activate any routes that are restored.
7750 SR OS Services Guide Page 1057