The icmp blackhole unreachable send command enables the switch to send a Destination Unreachable ICMP packet to an initiator when a tracert packet matches an IPv4 blackhole route.
The undo icmp blackhole unreachable send command disables the switch from sending a Destination Unreachable ICMP packet to an initiator when a tracert packet matches an IPv4 blackhole route.
By default, the switch is disabled from sending a Destination Unreachable ICMP packet to an initiator when a tracert packet matches an IPv4 blackhole route.
If static IPv4 blackhole routes are configured on the switch configured with the user access and authentication function, when a user goes offline, only the IPv4 blackhole route corresponding to the user's address segment exists on the switch. When a tracert packet matches the IPv4 blackhole route, the switch discards the packet. As a result, an initiator cannot detect that the user has gone offline.
After you run the icmp blackhole unreachable send command, the switch sends a Destination Unreachable ICMP packet to an initiator, notifying the initiator that the user has gone offline if a user goes offline and a tracert packet matches the IPv4 blackhole route.