QinQ Header size

When using an 802.1qtunnel does the number of CE-VLAN's pushed across the tunnel increase the frame size, or can i push as many inner vlan tags through without increasing the header size?

Form our testing every extra CE vlan added to a tunnel requires an extra 4 bytes added to the MTU to allow the traffic to flow.

Reply to
die.spam
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Every tunnel adds 4 bytes to Ethernet frame.

BR, A.C.

Reply to
Anonymous coward

Do you mean every VLAN adds 4 bytes to the frame?

Reply to
die.spam

No, every tunnel adds 4 bytes to the frame.

Reply to
Anonymous coward

Nope

assuming you use 802.1Q format packets (there is a cisco specific vlan flavour which is more complicated and that adds more overhead).

when you use 1 "layer" of vlan tags, you have 12 bits of vlan numbers you can use - you get approx 4000 vlans to work with, although some cisco setups will limit you to around 1000.

you can use more than 1 "layer" of vlans on a single packet.

eg if you take a carrier ethernet service, you might get a WAN ethernet interface with several vlans, each of which acts as a link to a different remote site, and inside that tunnel you can use your own vlans.

So 1 vlan tag on the packet used to tell the service provider where to send the packet, 1 customer vlan tag within that to select your target vlan, and inside that the meat of a normal Ethernet packet.

Total of 2 vlan tags per packet, 4 bytes overhead for each.

If you are getting more overhead than that something is set up wrong.

i suggest you get hold of a packet sniffer and see what is actually going out in the packets

Good luck

Reply to
Stephen

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