New install of SG135/AP100 causes ETH0 to flap


I am looking to commition again a Sophos SG135 device and a Sophos AP100 which expired some time ago and hasn't been used. I have installed a fresh copy of the XG firewall software using the ISO file HW-17.5.7_MR-7-511 and its currently running 17.5.7 (I know there is 17.5.8 available but I think that is a manual install now). The system activated at the Sophos end and it downloaded the AP firmware 11.0.009. All licenses are expired apart from the base firewall license and I was under the belief I could use this as a basic gateway with wireless functionality.

I configured the base wizard with ETH0 being LAN and ETH1 being WAN using DHCP, all other ports not configured or bridged. Eth0 goes into a POE switch which I have used for this project before. I have plugged in the AP100 into a port and it powers up and shows as unregistered in the XG interface, all good.

I then go to activate the wireless AP and just set the country and select default group, then select both the guest and SOPHOS networks as a test. The activation completes successfully but this is where we end up with a problem.

It appears the ETH0 then becomes unstable and starts flapping. This behaviour stops if I unplug the AP from the network. When I power the AP back on again the AP starts up and it gives me a red light as if the firmware is upgrading but then it stops during the process with an error that it can't send the file to the device and I am in the same situation with the flapping ETH0. During this time I can continually ping the AP and I don't believe its in a reboot loop (I have seen this in the past). What concerns me is if we're in an older firmware situation as the device has been sitting on a shelf for over a year.

I have attached a log export which shows the situation but isn't hugely helpful.

Anyone seen this before or has an idea of how to fix?




  • Hi adhodgson,

    The case required further investigation, I would recommend opening a support case with technical support.

  • Hi,

    I decided to have another stab at this last night as my WAP is out of warranty as is the appliance. I got it working in the end, it turns out its the cable that was causing the problem. I remembered what cable I used originally with this setup and tried that one, and the firmware updated and the WAP restarted without issue. It was weird behaviour though for the whole of ETH0 to flap like that especially as ETH0 is on a different cable coming from the switch and the other communication on the switch wasn't affected. Usually if it is a bad cable I wouldn't expect the WAP to start at all. Anyway no harm done and thanks.