Link flap on gigabit
Since some time I see link flaps every seveal minutes on some interfaces.
They occur only when the port is on gigabit. Setting the port to 100BaseTx solves the issue.
My first thought was that it was a cabling issue as gigabit uses 8 wires and 10/100mb only uses 4.
So I changed cables, switches, etc. but to no avail.
Then I took my spare firewall (same hardware, Jetway NF99FL-525 with AD3INLANG 3x intel NIC expansion card) and it showed the same issue on the same ports.
Looking at the ports that show the linkflaps, they're all on the expansion board. The two internal NIC's are rock stable.
Folowing step in the test was installing a generic Linux version (Debian wheezy) and run that for several days.
Connected all interfaces and run traffic on all of them. Result: no link flaps at all.
After all testing I'm quite sure it's not an hardware issue. It looks more like a driver problem.
Looking at the chip sets it turns out the on-board chipset is an intel 82574L while the expansion board uses Intel 82541PI.
resulting in using the Intel(R) PRO/1000 Network Connection 7.3.2 driver for the onboad chipset, and the Intel(R) PRO/1000 Legacy Network Connection 1.0.4 for the expansion board chipset.
So, I'm fairly convinced this is a driver issue.