ethernet RX/TX drops to zero, is it normal? No problems at all discovered

Я использую Debian Wheezy 7.1 [3.2.0-4-amd64 #1 SMP Debian 3.2.46-1+deb7u1 x86_64 GNU/Linux] and when monitoring eth0 via Slurm or built-in System monitor I am getting:

Current RX Speed: 1883.11 KB/s           Current TX Speed: 9123.94 KB/s

а потом

Current RX Speed: 0.00 KB/s              Current TX Speed: 0.00 KB/s

I have not discovered any problems with it, but is it as it should be?

Errors on Receiving: 0                Errors on Transmission: 0

System monitor graph