Disadvantages Of Sending Icmp Error Packets; Configuration Procedure - HP 3600 v2 Series Configuration Manual

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
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

The device stops sending "TTL timeout" ICMP error packets after sending ICMP timeout packets is
disabled. However, "reassembly timeout" error packets will be sent normally.
To enable sending ICMP error packets:
Step
1. Enter system view.
Command
system-view
109
Remarks
N/A