Knowledge checks

ICMP messages are carried in UDP segments using port number 86.

ICMP messages are carried directly in IP datagrams rather than as payload in UDP or TCP segments.

ICMP is used by hosts and routers to communicate network-level information.

ICMP communicates information between hosts and routers by marking bits in the IP header.

The TTL-expired message type in ICMP is used by the traceroute program.