Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6
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A. Conta, S. Deering, M. Gupta · 2006-03
Abstract
RFC 4443 specifies ICMPv6, the control message protocol for IPv6, which provides error reporting and informational messaging functions analogous to ICMP for IPv4. ICMPv6 also subsumes functions previously handled by ARP and IGMP, making it a more central protocol in the IPv6 stack than ICMP was in IPv4.
Why This RFC Matters
ICMPv6 is far more critical to IPv6 operation than ICMP was to IPv4, because IPv6 relies on it for Neighbor Discovery Protocol (NDP) — the replacement for ARP — as well as Multicast Listener Discovery (MLD) and router advertisement. Unlike IPv4, where firewalling ICMP was merely inconvenient, blocking ICMPv6 in an IPv6 network causes fundamental connectivity failures: hosts cannot resolve link-layer addresses, routers cannot announce prefixes, and path MTU discovery breaks entirely. RFC 4443's elevation of ICMPv6 to a core protocol dependency reflects lessons learned from IPv4 operational practice.