Troubleshooting TCP/IP

Troubleshooting packet errors

The netstat -i command displays active interfaces (network card and serial interfaces) as well as statistics on:

Ipkts: input packets per interface
Ierrs: input errors per interface
Opkts: output packets per interface
Oerrs: output errors per interface
Coll: packet collisions detected

Here is a sample output:

   Name  Mtu    Network       Address     Ipkts  Ierrs Opkts   Oerrs Coll
   net0  1500   172.16.118    don         1348   12    1854    23    65
   lo0   8232   loopback      localhost   4058   0     4058    0     0

In using netstat -i, you should verify that the card is receiving and sending packets (that Ipkts and Opkts are nonzero), and that input and output errors as well as collisions are a small percentage of the packet total.

If both Ipkts and Ierrs are zero, the connection to the network may be bad, the network card may be bad, or there may be an interrupt vector conflict. Verify network cabling, then check for interrupt conflicts by running hwconfig or vectorsinuse. If a conflict exists, use the Network Configuration Manager to reconfigure your card. If the cable and interrupt vectors check out, run any diagnostic tools supplied by the manufacturer of the networking card.

If Ipkts is zero, but Ierrs is nonzero, the network, cabling, or card may be bad, another host on the network may be generating bad packets, or the network may be incorrectly terminated.

If Opkts is zero and Oerrs is nonzero, there may be a conflict of I/O addresses on the system. If both are zero, the conflict may be in shared memory addresses. Verify the I/O and shared memory addresses of each card on your system, and reconfigure your networking card with other supported addresses if conflicts exist.

If Coll is high (greater than 1-2 percent of the Opkts total), your network is very busy. Consider breaking the network into multiple separate networks.