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rjickity
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Priority and VPLS

Wed Oct 17, 2012 5:24 pm

I have a question on the method to perform the following.

2 sites, connected via wireless bridge. I am considering VPLS over EoIP to go onto the link. The purpose is to encapsulate all vlans into it and pass across the link to come out the other side retaining their respective VLAN ID's. Illustration attached.

I have a few queries that i'd appreciate feedback on.

VPLS
1. What considerations to MTU should I make for the tagged frames. Working on a standard packet being 1500 - Is an MPLS MTU of 1526 correct for this setup (MPLS 4 + VPLS 4 + VLAN 4 + Ethernet 14).

Queues
2. To prioritise particular VLANs over the VPLS would the best way be to mangle as they come in on their respective VLAN interfaces in prerouting and then queue?

I dont have any equipment for testing this so i would like to get the theory set.

Cheers
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adairw
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Re: Priority and VPLS

Wed Oct 17, 2012 10:17 pm

My first thought is you don't need eoip and vpls, its one or the other.
You need to be running mpls to use vpls. I am not sure if eoip will allow you to trunk vlans through them or not
 
rjickity
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Re: Priority and VPLS

Thu Oct 18, 2012 1:01 am

i'm not using eoip on this. My comment "VPLS over EoIP" was said as in i have chosen to use VPLS over using EoIP. sorry for the confusion :)
 
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astounding
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Re: Priority and VPLS

Thu Oct 18, 2012 3:47 am

1500 (data) + 4 (802.1q VLAN tag) + 14 (ethernet frame) + 4 (inner VPLS tag) + 4 (innermost MPLS tag) + 4 (outer MPLS tag) = 1530, and bump that up to 1534 if you need to carry Q-in-Q double VLAN tagged packets.

If I understand it correctly, VPLS layer 2 encapsulation requires the VPLS tag, and a pair of MPLS tags (the inner is the end-to-end virtual circuit path tag, the outer the current hop link tag).

See http://wiki.mikrotik.com/wiki/Manual:Ma ... LS_ingress near the bottom.

Because I've always needed to carry Q-in-Q, the 1526 MTU limitations on many Routerboards has been a thorn in my side. I'm glad there are more choice coming out now supporting larger frame sizes.

If you don't use LDP, and if you manually configure MPLS tagging, maybe you could manually and statically set up a tag path that could eliminate one of the two MPLS tags. I'm not sure, I haven't tried. In that case you could indeed get within the 1526 limits of many Routerboards. Likewise, if the MPLS/VPLS parts ONLY traverse wlan interfaces, you're fine, as those support much larger frames, and your ethernet interface could spit out ordinary bridged ethernet frames.

Aaron out.
 
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mrz
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Re: Priority and VPLS

Thu Oct 18, 2012 10:32 am

You can disable control word usage (use-control-word=no) and get 4 byte smaller packet
 
rjickity
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Re: Priority and VPLS

Thu Oct 18, 2012 11:10 am

I'm looking for information on the MPLS MTU limitations but i cannot find anything definitive.

so with control word disabled i can achieve 1526 which will give me what i need. Correct me if i'm wrong but with SXT's i will not have an issue with MTU if i need to go >1526 (source: http://wiki.mikrotik.com/wiki/Manual:Ma ... uterBoards )

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