HP 6125XLG R2306-HP 6125XLG Blade Switch Layer 3 - IP Services Configuration G - Page 119

Configuring TCP timers, Enabling sending ICMP error packets

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Configuring TCP timers You can configure the following TCP timers: • SYN wait timer-TCP starts the SYN wait timer after sending a SYN packet. If no response packet is received within the SYN wait timer interval, TCP fails to establish the connection. • FIN wait timer-TCP starts the FIN wait timer when the state changes to FIN_WAIT_2. If no FIN packet is received within the timer interval, TCP terminates the connection. If a FIN packet is received, TCP changes connection state to TIME_WAIT. If a non-FIN packet is received, TCP restarts the timer, and tears down the connection when the timer expires. To configure TCP timers: Step 1. Enter system view. Command system-view 2. Configure TCP timers. • Configure the TCP SYN wait timer: tcp timer syn-timeout time-value • Configure the TCP FIN wait timer: tcp timer fin-timeout time-value Remarks N/A By default: • The TCP SYN wait timer is 75 seconds. • The TCP FIN wait timer is 675 seconds. Enabling sending ICMP error packets Perform this task to enable sending ICMP error packets, including redirect, time-exceeded, and destination unreachable packets. • ICMP redirect packets A host that has only one default route sends all packets to the default gateway. The default gateway sends an ICMP redirect packet to inform the host of a correct next hop by following these rules: { The receiving and sending interfaces are the same. { The selected route is not created or modified by any ICMP redirect packet. { The selected route is not destined for 0.0.0.0. { There is no source route option in the received packet. ICMP redirect packets simplify host management and enable hosts to gradually optimize their routing table. • ICMP time-exceeded packets A device sends ICMP time-exceeded packets by following these rules: { If a received packet is not destined for the device and the TTL field of the packet is 1, the device sends an ICMP TTL Expired in Transit packet to the source. { When the device receives the first fragment of an IP datagram destined for it, it starts a timer. If the timer expires before all the fragments of the datagram are received, the device sends an ICMP Fragment Reassembly Timeout packet to the source. • ICMP destination unreachable packets A device sends ICMP destination unreachable packets by following these rules: 111

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111
Configuring TCP timers
You can configure the following TCP timers:
•
SYN wait timer
—TCP starts the SYN wait timer after sending a SYN packet. If no response packet
is received within the SYN wait timer interval, TCP fails to establish the connection.
•
FIN wait timer
—TCP starts the FIN wait timer when the state changes to FIN_WAIT_2. If no FIN
packet is received within the timer interval, TCP terminates the connection. If a FIN packet is
received, TCP changes connection state to TIME_WAIT. If a non-FIN packet is received, TCP restarts
the timer, and tears down the connection when the timer expires.
To configure TCP timers:
Step
Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Configure TCP timers.
•
Configure the TCP SYN wait timer:
tcp timer syn-timeout
time-value
•
Configure the TCP FIN wait timer:
tcp timer fin-timeout
time-value
By default:
•
The TCP SYN wait timer is 75
seconds.
•
The TCP FIN wait timer is 675
seconds.
Enabling sending ICMP error packets
Perform this task to enable sending ICMP error packets, including redirect, time-exceeded, and
destination unreachable packets.
•
ICMP redirect packets
A host that has only one default route sends all packets to the default gateway. The default
gateway sends an ICMP redirect packet to inform the host of a correct next hop by following these
rules:
{
The receiving and sending interfaces are the same.
{
The selected route is not created or modified by any ICMP redirect packet.
{
The selected route is not destined for 0.0.0.0.
{
There is no source route option in the received packet.
ICMP redirect packets simplify host management and enable hosts to gradually optimize their
routing table.
•
ICMP time-exceeded packets
A device sends ICMP time-exceeded packets by following these rules:
{
If a received packet is not destined for the device and the TTL field of the packet is 1, the device
sends an ICMP TTL Expired in Transit packet to the source.
{
When the device receives the first fragment of an IP datagram destined for it, it starts a timer. If
the timer expires before all the fragments of the datagram are received, the device sends an
ICMP Fragment Reassembly Timeout packet to the source.
•
ICMP destination unreachable packets
A device sends ICMP destination unreachable packets by following these rules: