KB.15.15

Disabling ICMP destination unreachable messages

By default, when a HP 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:

Administration The packet was dropped by the HP device due to a filter or ACL

configured on the device.

Fragmentation-needed The packet has the "Don't Fragment" bit set in the IP Flag field,

but the HP device cannot forward the packet without fragmenting

it.

Host The destination network or subnet of the packet is directly

connected to the HP device, but the host specified in the destination

IP address of the packet is not on the network.

Network The HP device cannot reach the network specified in the

destination IP address of the packet.

Port 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 HP device, which in turn sends

the message to the host that sent the packet.

Protocol 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.

Source-route-failure The device received a source-routed packet but cannot locate the

next-hop IP address indicated in the packet's Source-Route option.

NOTE: Disabling an ICMP Unreachable message type does not change the HP device's ability

to forward packets. Disabling ICMP Unreachable messages prevents the device from generating

or forwarding the Unreachable messages.

Configuring ICMP 121