Disabling ICMP destination unreachable messages

By default, when a device receives an IP packet that the device cannot deliver, the device sends an ICMP unreachable message back to the host that sent the packet. The following types of ICMP unreachable messages are generated:


The packet was dropped by the device due to a filter or ACL configured on the device.


The packet has the "Don't Fragment" bit set in the IP Flag field, but the device cannot forward the packet without fragmenting it.


The destination network or subnet of the packet is directly connected to the device, but the host specified in the destination IP address of the packet is not on the network.


The device cannot reach the network specified in the destination IP address of the packet.


The destination host does not have the destination TCP or UDP port specified in the packet. In this case, the host sends the ICMP Port Unreachable message to the device, which in turn sends the message to the host that sent the packet.


The TCP or UDP protocol on the destination host is not running. This message is different from the Port Unreachable message, which indicates that the protocol is running on the host but the requested protocol port is unavailable.


The device received a source-routed packet but cannot locate the next-hop IP address indicated in the packet's Source-Route option.


Disabling an ICMP Unreachable message type does not change the device's ability to forward packets. Disabling ICMP Unreachable messages prevents the device from generating or forwarding the Unreachable messages.