Clarity on MSS and MRU /MRRU values

RouterOS Wireless Networking
1

I need calrity on the following please.

  1. Under pppoe-servers. Should the MAX MTU be 1500 for all sites to work? - The reason for this is that i have set my MAX MTU to 1480 and set the following mangle rule:
/ ip firewall mangle
add chain=forward protocol=tcp tcp-flags=syn action=change-mss tcp-mss=!0-1440 new-mss=1440

But that set and done i could not access sites such as yahoo mail and other sites.
i changed the MAX MTU to 1500 and set the /ppp profile to automatically change TCP MSS

/ppp profile
set default change-tcp-mss=yes

And that worked.
But i cant understand why.
At the moment all sites are working on one of my boards, and not all sites are working on the other. both mikrotik routerboards have MTU to 1500 and change-tcp-mss=yes or ppp profile.

  1. Does the MAX MTU and MAX MRU have to be the same values?
    Someone on this forum said that he changed the MRRU value to 1614 and that made browsing faster. i tried it to no avail.

  2. When setting the MTU and MRu values doe you have to consider the type of Antennas (at base / client-side) ? or does that have nothing to do with it?

2

These are various packet sizes. Almost always, it is 1500. But wit DSL and PPPoE, it is almost always lower because PPPoE uses some overhead. Read this to get a better understanding on those values and what they should be:
http://wiki.mikrotik.com/wiki/Manual:Interface/PPPoE

IF YOU ISP IS PPPOE OR DSL, YOU NEED TO CHANGE THOSE VALUES ON YOUR WAN INTERFACE!!!