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L2TP Over IPSec with Cisco 3600


I am trying to establish L2TP tunnel using IPSec. I have configured Cisco 3600 as LAC and also with the required IPSec configurations. When I try to establish L2TP tunnel using a PPP client connected to the LAC, the IPSec SA gets established properly and it forwards L2TP control packets also. After the L2TP tunnel establishment, Cisco 3600 (acting as LAC) is not able to forward PPP control packets over the IPSec tunnel. I could see an error message "IP ARP throttled out the arp request for A.B.C.D", for every PPP control packet sent from PPP Client. As far as I know, A.B.C.D should be the IPSec peer acting as LNS, but the actual address for LNS is something different (W.X.Y.Z). L2TP control packets are being sent properly to W.X.Y.Z, but only PPP negotiation packets are being sent to A.B.C.D which is in some other network, not related to LNS.

Any comments and suggestion in this regard would be most welcomed.



  • Other Security Subjects

Re: L2TP Over IPSec with Cisco 3600

Since there has been no response to your post, it appears to be either too complex or too rare an issue for other forum members to assist you. If you don't get a suitable response to your post, you may wish to review our resources at the online Technical Assistance Center ( or speak with a TAC engineer. You can open a TAC case online at

If anyone else in the forum has some advice, please reply to this thread.

Thank you for posting.