QinQ Header size

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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.

Re: QinQ Header size
On 19/5/11 12:51 AM, flamer die.spam@hotmail.com wrote:
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Every tunnel adds 4 bytes to Ethernet frame.

BR,
A.C.

Re: QinQ Header size
wrote:
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Do you mean every VLAN adds 4 bytes to the frame?

Re: QinQ Header size
On 20/5/11 3:06 AM, flamer die.spam@hotmail.com wrote:
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No, every tunnel adds 4 bytes to the frame.

Re: QinQ Header size
On Thu, 19 May 2011 18:06:09 -0700 (PDT), "flamer

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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
--
Regards

stephen_hope@xyzworld.com - replace xyz with ntl

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