HP 6125G HP 6125G & 6125G/XG Blade Switches Layer 3 - IP Services Conf - Page 81

Configuring ICMP to send error packets, Advantages of sending ICMP error packets

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received, the system restarts the timer upon receiving the last non-FIN packet. The connection is broken after the timer expires. 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 To configure TCP timers: Step 1. Enter system view. Command system-view 2. Configure the TCP synwait timer. tcp timer syn-timeout time-value 3. Configure the TCP finwait timer. tcp timer fin-timeout time-value Remarks N/A Optional. 75 seconds by default. Optional. 675 seconds by default. 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 the following types: • 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. • ICMP timeout packets If the device receives an IP packet with a timeout error, it drops the packet and sends an ICMP timeout packet to the source. The device sends an ICMP timeout packet under the following conditions: { 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 73

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73
received, the system restarts the timer upon receiving the last non-FIN packet. The connection is
broken after the timer expires.
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
To configure TCP timers:
Step
Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Configure the TCP synwait timer.
tcp timer syn-timeout
time-value
Optional.
75 seconds by default.
3.
Configure the TCP finwait timer.
tcp timer fin-timeout
time-value
Optional.
675 seconds by default.
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 the following types:
•
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.
•
ICMP timeout packets
If the device receives an IP packet with a timeout error, it drops the packet and sends an ICMP
timeout packet to the source.
The device sends an ICMP timeout packet under the following conditions:
{
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