Question: what are icmp message types?
Answer: Type 0 — Echo Reply.
Type 1 — Unassigned.
Type 2 — Unassigned.
Type 3 — Destination Unreachable.
Type 4 — Source Quench (Deprecated)
Type 5 — Redirect.
Type 6 — Alternate Host Address (Deprecated)
Type 7 — Unassigned.