Site to site  VPN

Posted on 2009-05-11
Last Modified: 2012-06-21
I have 2 sites with adsl connection and 2 Cisco 877 adsl routers. i would like to establish a vpn connection between the sites. My wan ip will change frequently so i am ready to use some dynamic dns service. Any one can help me how to configure the routers? please give me a sample configuration for both ends.
Question by:Achuthaprasad
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Expert Comment

by:Kerem ERSOY
Comment Utility

It is very Easy.
- Setup SDN to some comuter to manage the settings.
- Launch SDN. You need Java but the latest JRE6 is not compatible so downlad JRE5
- Logon to your router.
- Click Configure
- Click VPN
- You will see the options for both Site-Site and Client-To-Site. Even visual representations are there.
- For dynamic addresess. You'd like to set-up an account in Then there's a little agent which will run on one of your PC's and it will update your dynamic address as it changes.

This is it :)


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Accepted Solution

Quori earned 500 total points
Comment Utility
It's SDM, FYI. :)

Here is a generic config that you will need to modify but should work for both sites if filled out properly.
Be sure to deny the VPN traffic in your NAT ACL. For example, if the local subnet is and the remote is then your NAT ACL would look thus:

ip access-list extended TO_NAT
 deny ip
 permit any

You will need something similar for each endpoint so that the router doesn't try to NAT the traffic bound for the VPN tunnel. Also note this is a very basic Site-to-Site IPsec VPN tunnel. If you wanted to run a routing protocol or such over it you'd need to use GRE/IPsec tunnel. If this is the case, ask and this can be amended.

! Enable IP Domain Lookup and configure a name server or two

ip domain-lookup

ip name-server <ISP Name Server #1>

ip name-server <ISP Name Server #2>

ip name-server

! Configure DynDNS update service

ip ddns update method DynDNS


 add http://username:password@<s>/nic/update?system=dyndns&<a>

 interval maximum 10 0 0 0


ip host

! Configure IP SLA to always keep the tunnel up

ip sla 1

 icmp-echo <REMOTE INSIDE ENDPOINT> source-interface <INSIDE INTERFACE>

 frequency 30


ip sla schedule 1 life forever start-time now

! Create the transform set

crypto ipsec transform-set ESP-3DES-SHA esp-3des esp-sha-hmac

! Create a match-all isakmp pre-shared key

crypto isakmp key 0 somethingstrongerthanthis address

! Create the phase-1 details

crypto isakmp policy 10

 authentication pre-share

 encryption 3des

 hash sha

 group 2


ip access-list extended T0_VPN



crypto map VPN 10 ipsec-isakmp

 set transform-set ESP-3DES-SHA

 set peer

 match address TO_VPN



 ip ddns update hostname

 ip ddns update DynDNS host

 crypto map VPN


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Expert Comment

by:Kerem ERSOY
Comment Utility

It's SDM, FYI. :)

Thank you :)

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