ICMP router messages received


One of three ICMP router messages has been received.

Recommended action

No action required.

Detailed explanation

ICMP (Internet Control Message Protocol) is a reporting protocol for the IP component of TCP/IP. ICMP relays messages about the status of an IP connection.

The ICMP router message received is the secondary message displayed with this observation (see below).

Possible secondary messages

  • "Redirect" The router sends a redirect message to a host in the following situation; A router, G1, receives an Internet packet from a host on a network to which the router is attached. The router, G1, checks its routing table and obtains the address of the next router, G2, on the route to the packet's Internet destination network, X. If G2 and the host identified by the Internet source address of the packet are on the same network, a redirect message is sent to the host. The redirect message advises the host to send its traffic for network X directly to router G2 as this is a shorter path to the destination. The router forwards the original packet's data to its Internet destination. For packets with the IP source route options and the router address in the destination address field, a redirect message is not sent even if there is a better route to the ultimate destination than the next address in the source route.
  • "Router Advertisement" (See Router Solicitation, below)
  • "Router Solicitation" The ICMP router discovery messages are called "Router Advertisements" and "Router Solicitations". Each router periodically multicasts a Router Advertisement from each of its multicast interfaces, announcing the IP addresses of that interface. Hosts discover the addresses of their neighboring routers simply by listening for advertisements. When a host attached to a multicast link starts up, it may multicast a Router Solicitation to ask for immediate advertisements, rather than waiting for the next periodic ones to arrive; if and only if no advertisements are forthcoming, the host may retransmit the solicitation a small number of times, but then must desist from sending any more solicitations. Any routers that subsequently start up, or that were not discovered because of packet loss or temporary link partitioning, are eventually discovered by reception of their periodic (unsolicited) advertisements. (Links that suffer high packet loss rates or frequent partitioning are accommodated by increasing the rate of advertisements, rather than increasing the number of solicitations that hosts are permitted to send.) The router discovery messages do not constitute a routing protocol; they enable hosts to discover the existence of neighboring routers, but not which router is best to reach a particular destination. If a host chooses a poor first-hop router for a particular destination, it should receive an ICMP Redirect from that router, identifying a better one.
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    Other resources

    RFC 792 RFC 1256