BCP over L2TP supported?

Answered Question
Feb 24th, 2010
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Is there a Cisco box that performs (Ethernet) bridging over an IP network using for example BCP over L2TP?

Correct Answer by paolo bevilacqua about 7 years 3 months ago

It would be possible, I believe, to transport Ethernet frames over IP (maybe GRE?):


It may be possible, but officially unsupported.



If the MTU of the network is smaller than Ethernet's (1500) the frame will be broken down into more IP packets, reassembled at the other end so the complete Ethernet frame can be received.


Not so easy. IP Fragmentation is a layer 3 (routing) feature. Once you do bridging, layer 3 is out of the picture.


LTpv3 promoses to transport ethern over IP. In fact, is known to woork poorly.


So in short, do regular routing, or VPN, and everything will work fine.

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paolo bevilacqua Wed, 02/24/2010 - 07:20
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Not really. Part of the problem is that since you cannot transport full ethernet frames over the internet due to MTU, brdiging alones does not resolve the problem.

MCentrick2010 Wed, 02/24/2010 - 08:00
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Ok, I am probably wrong but I do not see it.


Let's forget about the BCP, L2TP complication.


It would be possible, I believe, to transport Ethernet frames over IP (maybe GRE?):


If the MTU of the network is smaller than Ethernet's (1500) the frame will be broken down into more IP packets, reassembled at the other end so the complete Ethernet frame can be received.


Isn't it?

Correct Answer
paolo bevilacqua Wed, 02/24/2010 - 08:12
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It would be possible, I believe, to transport Ethernet frames over IP (maybe GRE?):


It may be possible, but officially unsupported.



If the MTU of the network is smaller than Ethernet's (1500) the frame will be broken down into more IP packets, reassembled at the other end so the complete Ethernet frame can be received.


Not so easy. IP Fragmentation is a layer 3 (routing) feature. Once you do bridging, layer 3 is out of the picture.


LTpv3 promoses to transport ethern over IP. In fact, is known to woork poorly.


So in short, do regular routing, or VPN, and everything will work fine.

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