Configuration Procedure - HP A7500 Series Configuration Manual

ICMP timeout packets
2.
If the device receives an IP packet with a timeout error, it drops the packet and sends an ICMP timeout
packet to the source.
The device sends an ICMP timeout packet under the following conditions:
• If the device finds that the destination of a packet is not itself and the TTL field of the packet is 1, it
will send a "TTL timeout" ICMP error message.
When the device receives the first fragment of an IP datagram whose destination is the device itself,
•
it starts a timer. If the timer times out before all the fragments of the datagram are received, the
device will send a "reassembly timeout" ICMP error packet.
ICMP destination unreachable packets
3.
If the device receives an IP packet with the destination unreachable, it will drop the packet and send an
ICMP destination unreachable error packet to the source.
Conditions for sending an ICMP destination unreachable packet:
If neither a route nor the default route for forwarding a packet is available, the device will send a
•
"network unreachable" ICMP error packet.
• If the destination of a packet is local but the transport layer protocol of the packet is not supported
by the local device, the device sends a "protocol unreachable" ICMP error packet to the source.
When receiving a packet with the destination being local and transport layer protocol being UDP,
•
if the packet's port number does not match the running process, the device will send the source a
"port unreachable" ICMP error packet.
If the source uses "strict source routing" to send packets, but the intermediate device finds that the
•
next hop specified by the source is not directly connected, the device will send the source a "source
routing failure" ICMP error packet.
When forwarding a packet, if the MTU of the sending interface is smaller than the packet, but the
•
packet has been set as "Don't Fragment," the device will send the source a "fragmentation needed
and Don't Fragment (DF)-set" ICMP error packet.
Disadvantages of sending ICMP error packets
Sending ICMP error packets facilitates network control and management, but it has the following
disadvantages:
Increases network traffic.
•
A device's performance degrades if it receives a lot of malicious packets that cause it to respond
•
with ICMP error packets.
• A host's performance degrades if the redirection function increases the size of its routing table.
End users are affected because of receiving ICMP destination unreachable packets caused by
•
malicious users.
To prevent such problems, disable the device from sending ICMP error packets.

Configuration procedure

Follow these steps to enable sending of ICMP error packets:
To do...
Enter system view
Use the command...
system-view
93
Remarks
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