Cisco AnyConnect VPN Client - Connection Problems

[Protagoras]

I've not been back to check personally, but Friend A reports that this worked earlier last week, and then didn't again later in the week. The service provider has confirmed that there are no VPN restrictions or port blocks.

I've not had time to pop in again, so will try to have a look this week.

[woody1]

I'm not sure if it is a port issue because the VPN client does sound like it connects to the server, albeit only briefly.

If there was a port issue then the following may behave differently between Friend A's home office and Friend B's.

c:\>telnet VPN_server port

A quick google reveals that AnyConnect defaults to 443 but obviously it may have been configured to use a different port.

[LondonManc]

Sounds like a port issue at friend's office.

[Protagoras]

That's a good idea. I can setup various VPN types to my home router and test these.

[woody1]

To rule out a generic VPN issue (as opposed to AnyConnect specific), I'd try connecting to the internet through a different VPN.

Many browsers these days have built-in VPN, so you may not need to install anything to check this.

[Protagoras]

Friend A, when WfH, often works in Friend B's office premises locally.

Friend A's employer has issued him with a Windows laptop from which a Cisco AnyConnect VPN Client connects to the employer's office. This works perfectly from Friend A's home, from a mobile phone hotspot etc. But he said that it has stopped working from Friend B's office. I was sceptical, but sure enough, I watched it connect, then disconnect and fail to reconnect.

I've tested this with another laptop (different employer, same AnyConnect client) so that was using another business VPN and this is repeatable.

So it pretty much convinces me that there's a network issue with Friend B's office network. But Friend A reports that this worked up until about a week ago. The VPN client logs don't show much beyond the connection and attempt at reconnection.

Friend B's Internet connection looks to be ADSL, and is provided by a VOIP provider (as well as the Zyxel router, there's also a box for wireless VIOP handsets). Latency on the connection looks okay, and bandwidth is certainly adequate.

My current thoughts are
(a) provider has updated router firmware
(b) provider has blocked VPN traffic
(c) router is faulty

I did watch the router reboot when testing this. I now have the admin password for the router so can have a look but beyond checking firewall settings and perhaps checking for open tcp / udp ports, is there anything else I should be looking for?