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So, I was reading about the L2TP protocol and I understand what it basically does. But I fail to see why it would be preferred over pure IPSEC(VPN). VPN already provides end-to-end encryption between the gateway and my PC then why would I add more headers to the encapsulated packet and increase my bandwidth? Even if I am connecting one enterprise network located in two locations, can't we still do it via a pure VPN connection?

I think I am missing something very basic here. Can someone point it out! Thanks a lot.

-koundi

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The same question was asked on the Information Security SE. Here's my answer to that question:

L2TP/IPSec uses IPsec to protect the L2TP tunnel. So the real question is, why use L2TP?

Layer two tunneling protocol, as the name implies, provides a layer 2 link over an arbitrary L3 network. So, for example, if you needed to have a single VLAN appear in two locations (two data centers, for example), you can use L2TP to connect them together and appear as one logical VLAN/subnet, even though there is an arbitrary L3 network between them (like the Internet). Since you probably don't want your data center traffic traversing the Internet unprotected, you use IPSec to keep your traffic confidential.

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    Thanks for the answer! I just want to know one more thing. Is this the only uses case? Also why not just encapsulate the ethernet frame(or any other layer 2 protocol for that matter) instead of adding more headers?? As I understand the tunnel and session need to be created for l2tp tunel and the payload in a l2tp data message would be a ethernet frame – Koundinya Poluri Dec 26 '16 at 9:08

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