H3C Technologies H3C S12500 Series Switches - Manual (Page 138)

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Step Command Remarks
2. Configure TCP timers.
• Configure the TCP synwait timer:
tcp timer syn-timeout time-value
• Configure the TCP finwait timer:
tcp timer fin-timeout time-value
Optional.
By default:
• The TCP synwait timer is 75
seconds.
• The TCP finwait timer is 675
seconds.
IMPORTANT:
The actual length of the finwait timer is determined by the following formula:
Actual length of the finwait timer = (Configured length of the finwait timer – 75) + configured length of the
synwait timer
Configuring ICMP to send error packets
Sending error packets is a major function of ICMP protocol. In case of network abnormalities, error
packets are usually sent by the network or transport layer protocols to notify corresponding switches so
as to facilitate control and management.
Functions of sending ICMP error packets
ICMP error packets include the following types:
• ICMP redirect packets
A host might have only a default route to the default gateway in its routing table after startup. The
default gateway will send ICMP redirect packets to the source host, telling it to reselect a correct
next hop to send the subsequent packets, if the following conditions are met:
{
The receiving and forwarding interfaces are the same.
{
The selected route has not been created or modified by ICMP redirect packet.
{
The selected route is not the default route of the switch.
{
There is no source route option in the packet.
ICMP redirect packets function simplifies host administration and enables a host to gradually
establish a sound routing table to find out the best route.
• ICMP timeout packets
If the switch receives an IP packet with a timeout error, it drops the packet and sends an ICMP
timeout packet to the source.
The switch sends an ICMP timeout packet under the following conditions:
{
If the switch finds 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 switch receives the first fragment of an IP datagram whose destination is the switch
itself, it starts a timer. If the timer times out before all the fragments of the datagram are received,
the switch will send a "reassembly timeout" ICMP error packet.
• ICMP destination unreachable packets
The switch sends an ICMP destination unreachable packet under the following conditions: