ICMP is reporting network connectivity problems. In other words, a packet cannot reach its destination.
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.
If, according to the information in the router’s routing tables, the network specified in the Internet destination field of a packet is unreachable, the router may send a destination unreachable message to the Internet source host of the packet.
In addition, in some networks, the router may be able to determine if the Internet destination host is unreachable. Routers in these networks may send destination unreachable messages to the source host when the destination host is unreachable.
If, in the destination host, the IP module cannot deliver the packet because the indicated protocol module or process port is not active, the destination host may send a destination unreachable message to the source host. Another case is when a packet must be fragmented to be forwarded by a router, yet the Don’t Fragment flag is on. In this case, the router must discard the packet and may return a destination unreachable message.
The secondary message generated will depend on which part of the link could not be established.
Ensure that you have specified a valid target address.
Check for routing errors within your network.
Possible secondary messages
‘Network is unreachable’
‘Host is unreachable’
‘Destination is unreachable’
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