How to reset ifconfig counters?

Those counters are kept by the kernel, so your answer depends on how your network card driver is built. Two possible choices:

  1. Kernel module
  2. Inside the kernel

If it is second, you can not reset counters without restarting the operating system. If it is first, you can do it by unloading the module from the kernel and then loading it back again. If your NIC card use e1000 module, use following commands:

$ ifconfig eth0 down
$ modprobe -r e1000
$ modprobe e1000
$ ifconfig eth0 up

Use ethtool to find out your NIC module:

$ ethtool -i eth0

In front of driver you see your module name:

driver: e1000
version: 7.3.21-k8-NAPI
firmware-version: 
...

Use apt-get to install ethtool as follow:

$ apt-get install ethtool