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Topic Author
Posts: 39
Joined: Tue Nov 09, 2010 12:54 am

L2MTU question

Thu Feb 24, 2011 2:28 am

Hi to all,

My topology is the following:

RB493AH---Ether1----Microwave Gateway---VLANS 1, 3, 5-----Microwave Gateway---Ether1---RB493AH

I create 802.1q vlans on ether 1 and i send these vlans over a microwave device . Everything works OK (all VLANs pass correclty over the microwave link) , but there is one issue.

The management IP of the Microwave device is part of vlan 3 and there is an option in the microwave device that the ethernet frames going to this management IP can be tagged.

Everything fine so far. I can ping the management IP of the microwave device that is tagged to vlan3. The problems start when i move this configuration from Ether1 and going to another ethernet interface of the Mikrotik (for example Ether2) , then the management IP of the microwave is not accessible any more.

The only difference i found so far is the L2MTU which is 1526 for eth1 and 1522 for all other ethernet interfaces.

I tried changing it but it was not possible.

How could these four bytes affect that? I do not use QinQ or MPLS or VPLS, only 802.1q VLANS.

Any ideas?

Thank you



[admin@mikrotik] > interface print
Flags: D - dynamic, X - disabled, R - running, S - slave
0 ether1 ether 1500 1526
1 ether2 ether 1500 1522
2 ether3 ether 1400 1522
3 ether4 ether 1500 1522
4 ether5 ether 1500 1522
5 ether6 ether 1500 1522
6 ether7 ether 1500 1522
7 ether8 ether 1500 1522
8 R ether9 ether 1500 1522
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Posts: 285
Joined: Mon Mar 06, 2006 10:53 pm
Location: Whangarei, New Zealand

Re: L2MTU question

Sun Mar 06, 2011 2:07 am

In short - no, the L2MTU size shouldnt effect you, BUT you should try putting your MTU upto 1508 for example :)
Topic Author
Posts: 39
Joined: Tue Nov 09, 2010 12:54 am

Re: L2MTU question

Sun Mar 06, 2011 12:24 pm

Hi Belyivulk

i will give it a try. Thanks for the tip.


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