3Com Switch 8800 Advanced Software V5 Configuration Guide

240 CHAPTER 24: IP PERFORMANCE CONFIGURATION
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When performing hardware forwarding, Switch 8800s will not forward ICMP
destination unreachable packets even if the above conditions are satisfied.
Disadvantage of sending ICMP error packets
Although sending ICMP error packets facilitate control and management, it still
has the following disadvantages:
■ Sending a lot of ICMP packets will increase network traffic.
■ If the switch receives a lot of malicious packets that cause it to send ICMP error
packets, the performance will be reduced.
■ As the redirection function increases the routing table size of a host, the host’s
performance will be reduced if its routing table becomes very large.
■ If a host sends malicious ICMP destination unreachable packets, end users may
be affected.
To prevent such problems, you can disable the switch from sending ICMP error
packets.
Follow these steps to disable sending ICMP error packets:
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■ The switch stops sending "network unreachable" and "source route failure"
ICMP error packets after sending ICMP destination unreachable packets is
disabled. However, other destination unreachable packets can be sent
normally.
■ The switch stops sending "TTL timeout" ICMP error packets after sending ICMP
timeout packets is disabled. However, "reassembly timeout" error packets will
be sent normally.
Displaying and
Maintaining IP
Performance
To do... Use the command... Remarks
Enter system view system-view -
Disable sending ICMP redirect
packets
undo ip redirects Required
Enabled by default
Disable sending ICMP timeout
packets
undo ip ttl-expires Required
Enabled by default.
Disable sending ICMP
destination unreachable
packets
undo ip unreachables Required
Enabled by default
To do... Use the command...
Display current TCP connection state display tcp status
Display TCP connection statistics display tcp statistics
Display UDP statistics display udp statistics
Display statistics of IP packets display ip statistics [ slot slot-number ]
Display statistics of ICMP flows display icmp statistics [ slot slot-number ]
Display socket information display ip socket [ socktype sock-type ] [ task-id
socket-id ] [ slot slot-number ]