[c-nsp] What does L2PT actually do on the wire?

[Jeff Aitken]

On Wed, May 19, 2010 at 09:43:36AM +0100, Howard Jones wrote:
> My question though is: what is L2PT actually doing? My original 
> assumption was that it was encapsulating these packets in another frame 
> header, so they would no longer look like STP or CDP or whatever to 
> intervening devices. That doesn't appear to be the case though, or they 
> wouldn't get blocked.

The frame is not encapsulated, the destination mac addr is rewritten to
01:00:0c:cd:cd:d0.  At the far end of the "tunnel", the original mac is
restored.

For more info:

http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/l2pt.html
http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2ZY/configuration/guide/l2pt.html

Note that other vendors support the same behavior; e.g.:

https://www.juniper.net/techpubs/software/junos/junos92/swconfig-routing/configuring-layer-2-protocol-tunneling.html


--Jeff