3Com 5500-EI PWR - Disabling ICMP to Send Error Packets; Enabling Reception of Directed Broadcasts to a Directly Connected Network

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z finwait timer: When the TCP connection is changed into FIN_WAIT_2 state, finwait timer will be
started. If no FIN packets are received within the timer timeout, the TCP connection will be
terminated. If FIN packets are received, the TCP connection state changes to TIME_WAIT. If
non-FIN packets are received, the system restarts the timer from receiving the last non-FIN packet.
The connection is broken after the timer expires.
z Size of TCP receive/send buffer
Follow these steps to configure TCP attributes:
To do… Use the command… Remarks
Enter system view
system-view
—
Configure TCP synwait timer’s
timeout value
tcp timer syn-timeout
time-value
Optional
75 seconds by default.
Configure TCP finwait timer’s
timeout value
tcp timer fin-timeout
time-value
Optional
675 seconds by default.
Configure the size of TCP
receive/send buffer
tcp window window-size
Optional
8 kilobytes by default.
Enabling Reception of Directed Broadcasts to a Directly Connected Network
Directed broadcasts refer to broadcast packets sent to a specific network. In the destination IP address
of a directed broadcast, the network ID is the ID of network where the receiving interface resides and
the host ID is all-ones. Enabling the device to receive directed broadcasts will give hackers an
opportunity to attack the network, thus bringing forth great potential dangers to the network. Therefore,
the reception of directed broadcasts to a directly connected network is disabled on S5500-EI series
Ethernet switches by default. However, you should enable the feature when:
z Using the UDP Helper function to convert broadcasts to unicasts and forward them to a specified
server.
z Using the Wake on LAN function to forward directed broadcasts to a host on the remote network.
Follow these steps to enable the switch to receive directed broadcasts:
To do… Use the command… Remarks
Enter system view
system-view
—
Enable the device to receive
directed broadcasts
ip forward-broadcast
Required
Disabled by default.
Disabling ICMP to Send Error Packets
Sending error packets is a major function of ICMP protocol. In case of network abnormalities, ICMP
packets are usually sent by the network or transport layer protocols to notify corresponding devices so
as to facilitate control and management.
Although sending ICMP error packets facilitate control and management, it still has the following
disadvantages:
z Sending a lot of ICMP packets will increase network traffic.