GRE tunnel overhead?

Answered Question
Mar 28th, 2007

Can anyone tell me the overhead due to GRE tunnel?

Acc to my calculations, it will be:

Normal Packet = 66 bytes (including 6 bytes of MLPPP - L2 Header)

GRE tunnel overhead = 24 bytes + 6 (L2 ethernet header)

Total GRE tunnel = 24 + 6 + 66 = 96 bytes

i.e. 30 bytes extra w.r.t normal packet.

Is it correct?

I have this problem too.
0 votes
Correct Answer by royalblues about 7 years 3 weeks ago

It would be an additional 24 bytes overhead.

In the case of the GRE tunnel interface, the IP maximum transmission unit (MTU) is 24 bytes less than the IP MTU of the real outgoing interface. For an Ethernet outgoing interface that means the IP MTU on the tunnel interface would be 1500 minus 24, or 1476 bytes.

Hence most of the times it becomes necesarry to adjust the MSS or MTU while using GRE

Have a look at this link

http://www.netcraftsmen.net/welcher/seminars/intro-ipsec.pdf

HTH, rate if it does

Narayan

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Correct Answer
royalblues Wed, 03/28/2007 - 04:53

It would be an additional 24 bytes overhead.

In the case of the GRE tunnel interface, the IP maximum transmission unit (MTU) is 24 bytes less than the IP MTU of the real outgoing interface. For an Ethernet outgoing interface that means the IP MTU on the tunnel interface would be 1500 minus 24, or 1476 bytes.

Hence most of the times it becomes necesarry to adjust the MSS or MTU while using GRE

Have a look at this link

http://www.netcraftsmen.net/welcher/seminars/intro-ipsec.pdf

HTH, rate if it does

Narayan

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Posted March 28, 2007 at 3:44 AM
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