Weird problem with https connections

[Meldrew]

Hi everyone

We've got a weird problem that has cropped up. Hoping someone has suggestions about where to look.

 

Our trust has some web based services hosted at Site A which are have been working perfectly for years, including at Site B and site C.

 

Recently site A has switched from a leased line to an FTTP connection and also switched firewall from Endian to smoothwall. The port forwards, DNS, etc have been setup to host the services on the new FTTP connection. After doing this, the hosted services work everywhere (including from home, etc) except site B.

 

To be clear, there's no VPN's or any such other connectivity than the Internet connecting the sites.

 

At site B, http versions of the services load just fine, but when switching to https, the page fails to load and eventually times out. I've tried using openssl to diagnose, but got nowhere.

 

All the sites being smoothwall, I've tried using tcpdump and confirmed that data isn't being blocked by any firewall rule. In the end, I've installed wireshark on a PC at Site B and then made a test request to the https site. In wireshark, I can see the request going out and coming back in, but the browser is just eventually timing out. When I try using openssl, it looks like it never gets a response from the server, even though I can see a packet of data coming back. Specifically, the last 2 entries in wireshark show the client pc sending a 'Client Hello' packet and a response packet from the server.

 

Anyone got any suggestions about how to diagnose further or what might be happening?

 

Many thanks in advance,

 

Meldrew.