icmp

ICMP Message Types

Message types used by the Internet Control Message Protocol. Covers ICMPv4 (RFC 792) for IPv4 networks and ICMPv6 (RFC 4443) for IPv6 networks. Both protocols carry control and error messages between IP hosts and routers.

38 codes

references rfc-editor.org/rfc/rfc792 rfc-editor.org/rfc/rfc4443 iana.org/assignments/icmp-parameters/icmp-parameters.xhtml iana.org/assignments/icmpv6-parameters/icmpv6-parameters.xhtml

· All codes 38 codes

0 Echo Reply Sent in response to an Echo Request (type 8). Used by tools such as ping to confirm that a host is reachable and to measure round-trip time.
3-0 Destination Unreachable: Net Unreachable The router has no route to the destination network and cannot forward the datagram.
3-1 Destination Unreachable: Host Unreachable The router cannot reach the destination host on the directly attached network, typically because ARP resolution failed or the host is not responding.
3-10 Destination Unreachable: Communication with Destination Host Administratively Prohibited A firewall or access control policy is blocking traffic destined for the specific host.
3-13 Destination Unreachable: Communication Administratively Prohibited A filtering device (firewall or router ACL) is blocking the communication and has chosen to notify the sender rather than silently drop the packet.
3-2 Destination Unreachable: Protocol Unreachable The destination host does not support the transport-layer protocol specified in the IP datagram's Protocol field.
3-3 Destination Unreachable: Port Unreachable The destination host is reachable but no process is listening on the port specified in the datagram. Commonly seen with UDP when no service is bound to the target port.
3-4 Destination Unreachable: Fragmentation Needed and DF Set The datagram must be fragmented to traverse the next link, but the Don't Fragment (DF) bit is set. Used by Path MTU Discovery to signal the maximum transmission unit of a constraining link.
3-5 Destination Unreachable: Source Route Failed A datagram using IP strict or loose source routing could not be forwarded along the specified route.
3-6 Destination Unreachable: Destination Network Unknown The destination network is completely unknown to the router; no routing information of any kind exists for that network.
3-7 Destination Unreachable: Destination Host Unknown The destination host is not known to the router or gateway; the host has never been observed on the attached network.
3-9 Destination Unreachable: Communication with Destination Network Administratively Prohibited A firewall or routing policy is blocking traffic to the destination network.
3 Destination Unreachable Indicates that a datagram could not be delivered to its destination. A code value specifies the reason; see type 3 code entries (3-0 through 3-13) for details.
4 Source Quench Requested the source to reduce its transmission rate due to congestion. Deprecated by RFC 6633 and no longer sent by conformant implementations.
5 Redirect Sent by a router to inform a host of a better next-hop route to a destination. A code value distinguishes whether the redirect applies to a network, host, or type-of-service.
8 Echo Request Requests that the recipient return an Echo Reply (type 0) with the same data payload. The basis of the ping utility for connectivity testing.
9 Router Advertisement Sent by routers to announce their presence and provide routing parameters to hosts on a link. Part of the ICMP Router Discovery protocol.
10 Router Solicitation Sent by hosts to request that routers on the link immediately send a Router Advertisement (type 9) rather than waiting for the next scheduled advertisement.
11-0 Time Exceeded: TTL Exceeded in Transit The datagram's Time-to-Live field reached zero while being forwarded, causing the router to discard it. Exploited by traceroute to map network paths.
11-1 Time Exceeded: Fragment Reassembly Time Exceeded Not all fragments of a datagram arrived within the reassembly timeout window, so the partially reassembled datagram was discarded.
11 Time Exceeded Sent when a datagram is discarded because its Time-to-Live (TTL) reached zero, or because reassembly of a fragmented datagram did not complete in time. See code entries 11-0 and 11-1 for specifics.
12 Parameter Problem A router or host found an error in the IP header or options of a datagram and could not process it. The message includes a pointer to the offending byte.
13 Timestamp Request Requests that the recipient record the time of receipt and return a Timestamp Reply (type 14). Used for time synchronisation and one-way delay measurement.
14 Timestamp Reply Returns the originate, receive, and transmit timestamps in response to a Timestamp Request (type 13).
17 Address Mask Request Sent by a host to discover the subnet mask in use on its network segment. Superseded by DHCP and BOOTP; rarely used in modern networks.
18 Address Mask Reply Returns the subnet mask for the local network in response to an Address Mask Request (type 17).
icmpv6-1 ICMPv6 Destination Unreachable An IPv6 datagram could not be delivered to its destination. A code value specifies the reason: no route (0), administratively prohibited (1), beyond scope of source address (2), address unreachable (3), or port unreachable (4).
icmpv6-128 ICMPv6 Echo Request Requests that the recipient return an ICMPv6 Echo Reply (type 129) with the same data payload. The IPv6 equivalent of the ping echo request.
icmpv6-129 ICMPv6 Echo Reply Returned in response to an ICMPv6 Echo Request (type 128), carrying the same identifier, sequence number, and data. The IPv6 equivalent of the ping echo reply.
icmpv6-133 ICMPv6 Router Solicitation Sent by hosts when they come online to prompt routers on the link to immediately send a Router Advertisement rather than waiting for the next scheduled interval.
icmpv6-134 ICMPv6 Router Advertisement Periodically sent by routers, or in response to a Router Solicitation, to announce the router's presence and provide prefix, MTU, and configuration information for IPv6 Stateless Address Autoconfiguration (SLAAC).
icmpv6-135 ICMPv6 Neighbor Solicitation Used by a node to discover the link-layer address of a neighbour, verify that a neighbour is still reachable, or detect duplicate addresses during SLAAC. The IPv6 equivalent of ARP.
icmpv6-136 ICMPv6 Neighbor Advertisement Sent in response to a Neighbor Solicitation or to announce a link-layer address change, providing the link-layer address of the sender to its neighbours.
icmpv6-137 ICMPv6 Redirect Sent by a router to inform a host of a better first-hop router or that the destination is on-link. The IPv6 equivalent of ICMPv4 Redirect (type 5).
icmpv6-143 ICMPv6 Multicast Listener Report v2 Sent by a host to report its multicast group memberships to a local router, enabling the router to forward multicast traffic only to links with interested listeners. Part of Multicast Listener Discovery version 2 (MLDv2).
icmpv6-2 ICMPv6 Packet Too Big An IPv6 datagram could not be forwarded because it exceeds the MTU of the next-hop link, and IPv6 does not permit fragmentation by routers. Used by Path MTU Discovery to inform the source of the link MTU.
icmpv6-3 ICMPv6 Time Exceeded An IPv6 datagram was discarded because its Hop Limit reached zero in transit (code 0), or because fragment reassembly did not complete within the time limit (code 1).
icmpv6-4 ICMPv6 Parameter Problem A node encountered an error in an IPv6 header or extension header and could not process the packet. A code value distinguishes an erroneous header field (0), an unrecognised next header type (1), or an unrecognised option (2).