VPN behind ADSL modem???

Unanswered Question
Apr 30th, 2009

Hi experts,

I have ADSL internet connection with static IP. Behind the ADSL modem i have Cisco 871 with which i'm trying to make VPN tunnel with 3rd party organization. My ADSL wan interface has ip address x.x.x.40 and lan interface

My Cisco router has WAN ip and default route:

ip route int fa 4

VPN configuration is :

crypto isakmp policy 1

encr 3des

authentication pre-share

group 2

lifetime 3600

crypto isakmp key 6 fN?b?UCXW?uH-QKeqh7q#U6tMA%w2j address x.x.x.10 no-xauth



crypto ipsec transform-set sped-am esp-3des esp-sha-hmac


crypto map tunnel-map 10 ipsec-isakmp

set peer x.x.x.10

set transform-set sped-am

set pfs group2

match address 105


access-list 105 permit ip host x.x.x.x


interface fa 4

crypto map tunnel-map


Becouse i have to connect to 3rd party organization, they recognized me by my real ip that is on the WAN interface on my ADSL modem. That's why i am doing this:

crypto map tunnel-map local-address loopback 0

int loopback 0

ip add x.x.x.40


But still I can't make VPN connection with the organization!

What else I have to do ?

pls help!

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Collin Clark Thu, 04/30/2009 - 07:10

NAT on your cable modem is breaking it. What you need to do is setup your cable modem to bridge. Then the public IP address is assigned to the router.

Hope this helps.

zenon_electronics Wed, 05/06/2009 - 22:02

Hi, thank you for your help!

I know if i setup the cable modem to work as bridge it will work, but I need some way to do it without to be in bridge mode (if it is possible)! The reason that i want to do this is because i don't really have permission to make any changes to the ADSL modem.



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