3Com Switch 7750 Configuration Guide Guide

126 CHAPTER 15: IP PERFORMANCE CONFIGURATION
Configuring TCP
Attributes
Configuring to Send
Special IP Packets to
CPU
Usually the switch sends TTL timeout packets and unreachable packets to the CPU
in the process of forwarding IP packets. The CPU processes these special packets
after receiving them. Incorrect configuration and malicious attack will cause heavy
CPU load. You can perform the following configuration to configure not to send
corresponding packets to the CPU in order to ensure normal running.
Configuring to
Forward Layer 3
Broadcast Packets
n
Due to chip limitation, the Switch 7750 Family currently do not support the
forwarding of Layer 3 broadcasts.
Broadcast packets include full-net broadcast packets and directly-connected
broadcast packets. The destination IP address of a full-net broadcast packet is all
1s (255.255.255.255). A directly-connected broadcast packet is a packet whose
destination IP address is the network broadcast address of a subnet, but the
source IP address is not in the subnet segment. When a switch forwards this kind
of packet, the switch cannot tell whether the packet is a broadcast packet if the
switch is not connected with the subnet.
If a broadcast packet reaches the destination network after being forwarded by
the switch, the switch will receive the broadcast packet, for the switch also
belongs to the subnet. Since the VLAN of the switch isolates the broadcast
domain, the switch will stop forwarding the packet to the network. Using the
Tabl e 69 Configure TCP attributes
Operation Command Description
Enter system view system-view -
Configure timeout time for
the synwait timer in TCP
tcp timer syn-timeout
time-value
Required
The default value is 75
seconds
Configure timeout time for
the finwait timer in TCP
tcp timer fin-timeout
time-value
Required
The default value is 675
seconds
Configure the socket
receiving and sending buffer
size of TCP
tcp window window-size
Required
By default, the size of the
socket receiving and sending
buffers is 8 KB
Tabl e 70 Configure to send special IP packets to CPU
Operation Command Description
Enter system view system-view -
Configure to send TTL
timeout packets and
unreachable packets to CPU
ip { ttl-expires |
unreachables }
Required
By default, unreachable
packets are not sent to the
CPU, while TTL timeout
packets are sent to the CPU