pppoe over eoip mtu

RouterOS Beginner Basics
1

please be patient, I know this is the 1000000-nth question about this topic but is evident that this question is a square an I am a circle.

I have a routed network.
I have an pppoe server, reachable from access points, with mtu of 1500 (ping unfragmented 1500).
I create an eoip tunnel from each AP to the server; eoip have mtu=1500.
A pppoe connection from a user, uses eoip tunnels to reach pppoe server.

QUESTIONS:

  • what is the best mtu for eoip ?
  • what MTU to set in pppoe server and pppoe client ?
  • what MRU to set in pppoe server and pppoe client ?
  • must I adjust mtu of wlan and eth interfaces ?

thanks 1000001

2

This is trivial to figure out with Google once you get what to look for. Hopefully the below helps you.

EoIP is GRE, so it adds 4 bytes of overhead. PPPoE adds 8 bytes of overhead. If you have a path MTU of 1500 bytes and are transporting PPPoE over EoIP you should set the PPPoE MTU and MRU to (1500 - 4 - :sunglasses: = 1488 bytes.

Of course you don’t touch the physical interfaces. They can transport 1500 bytes, after all. That is your physical path MTU. You just subtract the header overhead of all protocols encapsulating each other along that path.

3

well!
I can say that the mtu=1480 in pppoe server mikrotik default is at least correct ?

thank you.

4

Not sure what you mean - it’ll certainly work. It’s a slightly more conservative default value.