NTP not sync'ing - what interface is used?

Interesting. I think all the firewall rules have been configured going out, so it might be that work is required on the inbound traffic instead.

Our network guys have confirmed that traffic is going out ok, but I don't think in all of our conversations we've even considered traffic coming in. I think because this is working on another set of F5s (on a different network) it was assumed to be allowed.

I will take this up with them in the morning and report back my findings!

Thanks all for the assistance so far.