Hi guys,

I'm a little confused about mtu and l2mtu configuration/aspect of my new laboratory network setupped in this holidays!

Network is composed of some RB411AH partecipating in a OSPF network (I call backbone);
over OSPF network I have operated the setup of MPLS network;
over mpls network there are olso vpls link between other RB411AH (who have radio for accept connection of remote client) and a centralized PPPoE Server hosted on RB411AH.

After reading wiki, forum posts ecc. about MTU I have now some perplexity about my configuration; I try to explain:

In according of the reading (MTU on official mikrotik wiki http://wiki.mikrotik.com/wiki/Maximum_T ... uterBoards) "Make sure that MPLS MTU is smaller or equal to L2MTU"... but I have:
-in all RB411AH that partecipate in the mpls cloud the default value of mpls-mtu of 1508
-in other interface bridge1 and vpls (as seen with /interface print command) I have the l2mtu value

I must modify the l2mtu value of the bridge1 and vpls interface to the 1508 value?
I do not want packet fragmentation!!

Just to clarify che bridge1 interface is present on my rb411 board who host the pppoe-server;
the pppoe-server listen on bridge1 and bridge1 contain all vpls to the remote rb411 who accept wireless connection from the remote wireless client (that have the pppoe-client).

Thanks in advance and best regards.
Luciano

To forward 1500 byte packet inside VPLS without fragmentation you have to set MPLS MTU to
1500+14+4+4+4=1526. Also make sure that all interfaces in LS Path has L2MTU set to at least 1526.

To forward 1500 byte packet inside VPLS without fragmentation you have to set MPLS MTU to
1500+14+4+4+4=1526. Also make sure that all interfaces in LS Path has L2MTU set to at least 1526.

Hi Mrz,
thank you for prompt reply.
I must set MPLS MTU =1526 on all router board that partecipating in the mpls or only in the routerboard that have vpls links configured?
I don't understand what is "LS Path"?
When you tell to set l2mtu valute at least 1526 you think that the value must set olso for virtual interface such as vpls and bridge?

Thanks in advance.
Regards.
Luciano

LSP is Label Switched Path. This is the path through the MPLS network.

You must set MPLS MTU =1526 on all router board that partecipating in the mpls.
L2MTU must be >=1526 on all interfaces that are added to LDP interfaces and can be used in LSP.

LSP is Label Switched Path. This is the path through the MPLS network.

You must set MPLS MTU =1526 on all router board that partecipating in the mpls.
L2MTU must be >=1526 on all interfaces that are added to LDP interfaces and can be used in LSP.

Ok, but the value of 1526 is valid if I want to forward 1500 byte packet inside VPLS.
I think, in my scenario, that i must forward only 1480 byte (not 1500) so the correct value of mpls mtu in my scenario is 1506 ?

Thanks in advance.
Luciano