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horizn
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MPLS MTU between 433AH and 411A

Fri Jul 16, 2010 10:50 am

hi, here we have a scenario:
http://wiki.mikrotik.com/wiki/Transpare ... using_MPLS

there is RB433AH as Ap bridge connected to switch thru eth2 or eth3 (currently i cant use eth1). RB411A works as station, now we have informaton, that:
Note: If interface does not support L2MTU specified as mpls-mtu, then packets will be silently dropped
RB433 have L2MTU 1522 (on eth2 and eth3), RB411A have L2MTU 1526.

will it work or not?
 
Mplsguy
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Re: MPLS MTU between 433AH and 411A

Fri Jul 16, 2010 5:58 pm

If you have your VPLS tunnel going only over wireless link (which is the case in wiki example), you do not have to worry about ethernet l2mtu - only l2mtu-s you care about are for interfaces that are involved in actual VPLS tunnel. And wireless has big enough l2mtu by default. Wiki example actually was not correct in referring to ethernet l2mtu, this has been fixed.
 
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horizn
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Re: MPLS MTU between 433AH and 411A

Sat Jul 17, 2010 7:26 pm

If you have your VPLS tunnel going only over wireless link (which is the case in wiki example), you do not have to worry about ethernet l2mtu - only l2mtu-s you care about are for interfaces that are involved in actual VPLS tunnel. And wireless has big enough l2mtu by default. Wiki example actually was not correct in referring to ethernet l2mtu, this has been fixed.
what if i try to connect another 433ah to existing (thru ether2 or 3) in the same scenario like described in my first post?
 
Mplsguy
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Re: MPLS MTU between 433AH and 411A

Mon Jul 19, 2010 11:30 am

Like I said - you have to take into account l2mtus of links that are involved in MPLS network - links over which MPLS packets are sent, no matter what MPLS application you are using, be it "simple" MPLS forwarding of IP packets or VPLS.

If you intend to forward MPLS traffic (with VPLS inside it) over ethernet between those RBs - yes, you have to set up mpls-mtu on all MPLS routers to the value that ensures forwarding over all links. Remeber that VPLS between RouterOS routers do fragment VPLS packets if they exceed mpls-mtu, so in case you can not provide links with sufficent l2mtus, adjust mpls-mtu on all routers appropriately and VPLS frames will be fragmented.

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