If a LAN client sends an ARP Request to a Vigor AP903 WiFi client, the Response does not make it back to the LAN client. ARP "Announcements" and Requests in the other direction do work.

This means that if a WiFi client boots/gets a DHCP address before an associated LAN client, that LAN client will not be able to communicate with the WiFi client. If the WiFi client tries to access the LAN client, this succeeds and populates the LAN client's ARP cache, so that it now works in both directions. The client type appears to be irrelevant.

This is reproducible at will with the Vigor AP903 running V1.4.2 (for some reason, SYS VER says it's 1.4.2RC2 - but the firmware image is identical to that on the website).



192.168.100.2 (the "WiFi client") was a Windows 10 Pro 64bit client running on a laptop, connected to the AP903 via 2.4GHz WiFi.
192.168.100.6 (the "LAN client") was a Windows 10 Pro 64bit client, accessing the AP903 via a Netgear GS108T switch and a GS105E switch.

Needless to say, if you try the same experiment with a node that is not a WiFi client of a Vigor AP903, you cannot reproduce this behaviour - the ARP cache simply repopulates. I can see from Wireshark, that the ARP Request makes it to the WiFi client and it responds. That Response gets discarded somewhere along the line.

I think this explains all manner of strange oddities I have seen over the last 18 months!

Of course, when encountering this problem, most people will drop the WiFi connection and re-establish it, which works-around the problem. (The LAN client will probably hear the ARP Probe and populates its ARP cache from that.)

Every contact with Draytek Support, is less impressive than the last ...

Draytek wrote: --- Please do not reply below this line ---

Can you please give us a call and we will investigate further https://draytek.co.uk/support/contact-support

Regards,
James

Do you think they want me to read all that out to them?

Given the seeming reluctance of Draytek Support to even accept there's a problem, I thought I'd do some more investigating.

With the Vigor AP903 reset to Factory Settings and plugged into a standalone Windows 10 PC, I tried to reproduce the issue with a variety of WiFi clients; I couldn't.

So it seems possible/likely, that this is to do with the multi-VLAN configuration I have. I tried putting my Vigor AP802 at the same position in the infrastructure as the Vigor AP903 normally resides (so complete with the Netgear switches). I couldn't reproduce the issue with that either. Re-introducing the Vigor AP903 brought the fault back.

So, I can try and get Draytek Support interested - or put the Vigor AP903 on eBay and replace it with something else

Having now got it into a state where it can be reproduced using a Vigor AP903, a PC and the wireless client of your choice, I suppose I'm going to have ring Draytek

Having finally got to the end of the music-on-hold, I spoke to an affable guy, with a South African accent. (He had the accent; I didn't put one on to speak to him :wink: )

He had no idea who James is, no idea why I didn't have a ticket number and no idea why I'd been asked to call. He suggested I start again at the beginning

I have re-submitted this. Ticket no. DQ498561

(It turns out that the response to the first one did include a ticket no. (#DQ633079), but only in the Subject line. The subject line was too long to allow it be displayed in my Mail client (separate bug!).

In the meantime, I've removed the AP903 from my setup and replaced with a GS105Ev2 switch, an old Vigor 2830n and a Fritzbox 7530. It's all a bit unwieldy, but has a slight advantage, in that it WORKS