9800 WLC Web Gui MTU issue

[NGJ]

Hi. I have a WLC 9800 (V17.03.04c).  With a laptop directly connected to the Service Port I am able to access the Web GUI.  However, when I attach the Service Port to our network I am unable to access.

The lowest MTU on one hop in the network is 1422.  The workaround is to set the MTU on my laptop to 1422, then I am able to access.  Any reason why the WLC has these issues with the web gui.  I tried to lower the MTU on the Service Port (Gi0) but the lowest I can set is 1500

Situation is the same for http/https, and whether I use local or TACACS authentication.  

Thanks

[Flavio Miranda]

Hi

 Any reason for the MTU to be at 1422?  1500 should be the standard for Ethernet

[NGJ]

Thanks, I appreciate 1500 is standard.  The WLC is located at a remote site so we access over a WAN link, hence the drop in MTU size.  However, we have no issue accessing any other web resources over this link when packets are fragmented.  The issue is just when we access the WLC web gui.  Can that not cope with fragmented packets?

[Flavio Miranda]

I have never heard or saw this happening.  Besides that, the WAN link is not connected to the Service Port, is it?  I mean, must be a router and a switch before the WLC and the packet should get to the WLC with 1500 though.

[NGJ]

Yes, routers are either end of WAN link, then switches.  The only way I can access the web gui is to drop MTU on my laptop to match lowest MTU in the path.  I only need to do this to access WLC and nothing else.  Very odd.

[Flavio Miranda]

Sounds more like a Bug.  I tried to find one but no luck so far. It can be an unkown Bug.

 Your topology seems to be very common. If you have the chance, open a TAC. This is not normal that´s for sure.

[NGJ]

Yeah thats a good call.  Thanks for the responses