4285ch03.fm Draft Document for Review May 4, 2007 11:35 am
88 Linux Performance and Tuning Guidelines
Figure 3-2 KDE System Guard network monitoring
It is important to remember that there are many possible reasons for these performance
problems and that sometimes problems occur simultaneously, making it even more difficult to
pinpoint the origin. The indicators in Table 3-3 can help you determine the problem with your
network.
Table 3-3 Indicators for network analysis
Network indicator
Analysis
Packets received
Packets sent
Shows the number of packets that are coming in and going out of the
specified network interface. Check both internal and external interfaces.
Collision packets Collisions occur when there are many systems on the same domain. The
use of a hub may be the cause of many collisions.
Dropped packets Packets may be dropped for a variety of reasons, but the result may affect
performance. For example, if the server network interface is configured to
run at 100 Mbps full duplex, but the network switch is configured to run at
10 Mbps, the router may have an ACL filter that drops these packets. For
example:
iptables -t filter -A FORWARD -p all -i eth2 -o eth1 -s 172.18.0.0/24
-j DROP
Errors Errors occur if the communications lines (for instance, the phone line) are of
poor quality. In these situations, corrupted packets must be resent, thereby
decreasing network throughput.
Faulty adapters Network slowdowns often result from faulty network adapters. When this
kind of hardware fails, it may begin to broadcast junk packets on the network.
