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HP A7500 Series Configuration Manual: Configuring Tcp Timers; Configuring Icmp To Send Error Packets; Introduction

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Configuring TCP timers

You can configure the following TCP timers:
synwait timer: When sending a SYN packet, TCP starts the synwait timer. If no response packet is
received within the synwait timer interval, the TCP connection cannot be created.
finwait timer: When a TCP connection is changed into FIN_WAIT_2 state, the finwait timer is
started. If no FIN packet is received within the timer interval, the TCP connection is terminated. If a
FIN packet is received, the TCP connection state changes to TIME_WAIT. If a non-FIN packet is
received, the system restarts the timer upon receiving the last non-FIN packet. The connection is
broken after the timer expires.
Follow these steps to configure TCP timers:
To do...
Enter system view
Configure the TCP synwait timer
Configure the TCP finwait timer
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. In case of network abnormalities, error packets are
usually sent by the network or transport layer protocols to notify corresponding devices so as to facilitate
control and management.
Advantages of sending ICMP error packets
ICMP error packets include redirect, timeout, and destination unreachable packets.
ICMP redirect packets
A host may have only a default route to the default gateway in its routing table after startup. If the
following conditions are satisfied, 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:
The receiving and forwarding interfaces are the same.
The selected route has not been created or modified by an ICMP redirect packet.
The selected route is not the default route of the device.
There is no source route option in the packet.
The ICMP redirect packets function simplifies host administration and enables a host to gradually
establish a sound routing table to find the best route.
Use the command...
tcp timer syn-timeout time-value
tcp timer fin-timeout time-value
75 seconds by default.
675 seconds by default.



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