While I agree that knowing the precise MTU that works would be enlightening, I find it hard for me to believe it is related to the extended ethernet framesize caused by vlan tags. It is possible that the bridge / switch interface changes in v7.2 are limiting the ethernet frames (L2 MTU + FCS) to 1518 instead of 1522, but I would guess if that was the case, there would be many more complaints than we have seen, but then again it is possible that not that many users are using vlans. There are some weird issues that have been reported with bridge vlans working on 6.48.6 but not on 7.2 (this was related to a trunk port between a hEX S and a hap ac lite).
First, in my experience, I have never seen ethernet packets containing ethernet frames with vlan header being dropped because they are too long, at least when using switches made in the last 15 years, and as long as the L2 MTU isn’t dropping L2 ethernet packets > 1518, then tagged frames shouldn’t affect the L3 MTU, at least that’s my understanding. i.e. a tagged frame won’t get a L3 MTU of 1504, the vlan interface shim driver has already untagged the frame before the ip driver receives the IP packet. Every “dumb” switch I have ever tested will transparently pass tagged vlans as is. Of course they can’t untag them, or filter based on ports, and I don’t recommend using dumb switches to carry tagged traffic, but I have done it myself many times in a lab environment.
Also, if if was the vlan tag, why wouldn’t it affect all sites, instead of just specific ones?
I think there is more involved than @tikker is sharing. Perhaps a vpn ?
But I will admit that my
usually the symptom is that web sites will open, but then hang
is probably an outdated observation.