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Will Mikrotik v7 support L2MTU for x86?

Sat Jan 23, 2021 11:10 pm

Hi.
Will Mikrotik v7 support L2MTU for x86?
I have an Intel X710 DA-2 card to experiment with.
The card is determined by the OS and everything works. But for MPLS, you need to raise MTU. And if I understand correctly, if I do it manually, then there will actually be packet fragmentation.
Thank you.
 
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Re: Will Mikrotik v7 support L2MTU for x86?

Mon Jan 25, 2021 10:53 am

If you increase MTU and, for example, set MPLS MTU to 1504, then there will be no fragmentation for mpls (assuming that forwarded ip packet is 1500bytes).
There will not be MTU problems also for forwarded IP packets over the routers since packet size is determined on packet originator.
There can be problems only with non-tcp IP traffic originated from router itself.
 
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Re: Will Mikrotik v7 support L2MTU for x86?

Mon Jan 25, 2021 10:43 pm

You're right.
But in this case, will we have to stop using VLAN or VPLS?
 
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Re: Will Mikrotik v7 support L2MTU for x86?

Tue Jan 26, 2021 9:57 am

If mpls MTU is set up correctly, then it does not affect VPLS at all.
For vlans on physical interfaces limitation is the same as on physical interface (only router originated non-tcp traffic can have problems )
 
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Re: Will Mikrotik v7 support L2MTU for x86?

Tue Jan 26, 2021 9:47 pm

On MPLS interfaces, MTU is by default 1508.
The question is as follows.
If you pass the VLAN through the physical link and raise MPLS on it, then problems begin with the passage of packets more than 1496 bytes. If you raise the MTU on the physical card to 1504, then 1500 bytes packets begin to pass through the VLAN interface. But in this case, as I noticed, one of the processors on the server is loaded. And the traffic to the client does not go as it should. The speed is low.
So I thought that, in fact, by manually raising the MTU, the OS cannot actually raise the card L2MTU, but emulates a large package programmatically.

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