topic Re: Business Hub ARP Broadcast Problems in Broadband

Business Hub ARP Broadcast Problems

Raymo — Thu, 22 Feb 2018 12:26:23 GMT

Hi all,

We have a BT Business Hub 3.0 (Version 4.7.5.1.83.8.82.1.1 [Type A]) with several wireless and Ethernet devices connected.

I've having some trouble with connecting from wired devices to some embedded wireless modules we're trying out: I think that this is down to the Hub not passing on ARP messages from the Ethernet side to the wireless side. For example, if I ping one of the wireless modules from my PC I don't get any replies but as soon as I ping the PC from the wireless module I can ping it back from the PC with no trouble. After a while the IP/MAC address is dropped from the ARP cache table on my PC and I can no longer ping the module. If I add a static ARP entry for the module to the ARP cache on the PC then I can always ping it.

With Wireshark on the Ethernet I can see my PC sending an ARP request for the wireless module but it does not get a reply. Running Wireshark on the wireless side I can't see the PC's ARP requests at all.

I've tried the same test with both an old Netgear and Thomson access points and these work as expected -- the ARP broadcasts go in both directions and I can connect at will from the PC to the module.

Is there some hidden setting on the Business Hub that I've missed or may have messed up? Is this a fault or bug on the Hub that anyone else has spotted?

I tried a BT Home Hub 2.0 (Version 8.1.H.U[Type A]) and a BT Business Hub 2700HGV, both of which work without a hitch.

Re: Business Hub ARP Broadcast Problems

DazzaSlayer — Thu, 22 Feb 2018 12:28:13 GMT

Hi @raymo

What happens if you set a static route within the hub its self to a local static applied to the wireless device?

that's in settings > advanced settings > Broadband > routing

Let me know how ou get on with that

Re: Business Hub ARP Broadcast Problems

Raymo — Thu, 22 Feb 2018 12:29:19 GMT

Hi Dazza

How very odd... I went to the routing page on the Hub but could not add a new static route as there was one alredy in the list for the subnet (192.168.0.0/255.255.0.0; gw=0.0.0.0; if=br0). I noticed a section at the bottom for "Dynamic Routing" that was set to "No". I though "why not" and changed it to "Yes" and suddenly everything works as it should. Don't know if it was trying to add the route or enabling Dynamoc Routing that did it.

The weird thing is that I then changed the Dynamic Routing back to "No" and it still works so I'm very confused -- unless changing the setting back and forth and saving it corrected something that was corrupt in the Hub's flash before.

I'll keep testing it for the next few days, not sure if this is a soulution as such but I'll mark the thread as solved if it's still working tomorrow

Thanks.