I started to experience a problem with a certain site not loading, now I'm down a rabbit hole. I am fairly certain there is an MTU issue somewhere, but I cannot find out how to find it.
I have a bunch of Mikrotik devices connected to each other via wireless link, ethernet or fibre.
Routing protocol is OSPF and MPLS/VPLS (MPLS-MTU 1526) is used over the network to transport PPPoE from end sites to the core.
So how could I trace the MTU problem? If I VPN out of my network (or just out of the pppoe concentrator) then the site(s) (I found a few more) load.
pinging each end site with 1500 bytes and DF does not give any issues. I am kind of at a loss here. Does anyone have any recommendations on how to actually troubleshoot something like this?
Code: Select all
<------------------------VPLS-------------------->
CORE ---> Distribution --- fibre ------> end site
--- ethernet--> end site
---wireless---> end site
as soon as this rule is added, everything loads
Code: Select all
add action=change-mss chain=forward disabled=yes new-mss=clamp-to-pmtu \
passthrough=yes protocol=tcp tcp-flags=syn