User Guide

Appendices.....127
Appendix G:Appliance Troubleshooting
LAN performance
If you're experiencing issues between the appliance and the network, issue the ethtool eth0 or
ethtool eth1 command to determine if the appliance is communicating with the network switch at
half duplex. This can happen if the network switch is not set to auto-negotiate speed and duplex
(the appliance only supports auto). When a network switch is static and the appliance is auto, the
two will not be able to communicate with matching duplex, leading to poor network peformance.
To resolve this, have the network administrator set the network switch port to auto-negotiate speed
and duplex.
To assist in troubleshooting issues related to connectivity, sessions, time-outs or other network-
related problems, a network traffic packet capture may be performed. At the appliance shell,
execute the tcpdump command on one interface at a time that lies within the communication path
between the user-appliance and the appliance-target. Save the output of the tcpdump to the
/download directory, then copy the output file to a workstation for analysis using tools such as
WinSCP and Wireshark.
For example, to capture from both the eth0 and the priv interfaces:
tcpdump -i eth0 -w /download/networktrace1.cap and tcpdump -i priv -w
/download/networktrace2.cap
WAN performance
If KVM, virtual media or firmware uploads are slow or fail across a network WAN, many network
routers that connect to WAN links (Frame Relay, ATM, SONET or VPN) often are set to fragment
large IP packets into smaller chunks. The maximum size of an IP packet is defined as MTU within
all devices connecting to networks. The appliance's MTU defaults to 1500 bytes and the appliance
sends all traffic with the "Don't Fragment" bit enabled in the IP header. An IP packet that doesn't
want to be fragmented is discarded by a router that must fragment large packets before
transmitting them across a WAN link.
To resolve this, you can decrease the size of the appliance's MTU in the network settings, which will
generate smaller IP packets. This will increase the total number of packets that get created, but
they will be small enough to cross the WAN link without being discarded and should improve the
situation. Don't do this unless you are sure that the appliance traffic is being discarded by the
customer WAN router because of fragmentation.