Tech Master Guide

First of all its possible to do the site to site VPN with help of IPSec technology from one router to the remote Router.

You just have to note the WAN interface IP addresses in both side, if the connection type is adsl with dynamic IP address then there might be occur some problems..

I will give a brief idea about the setup and you just need to follow the same:-
These steps to be done on one side and the same steps must be repeated on the other side too.
The encryption of data will depend on a shared-key. This way, you will not need specialized CAs or RSA methodologies.

1. Create Internet Key Exchange (IKE) key policy. The policy used for case is policy number 9, because this policy requires a pre-shared key.

Router(config) #crypto isakmp policy 9

Router(config- isakmp)#hash md5

Router(config- isakmp)#authentication pre-share

2. Setup the shared key that would be used in the VPN,

Router(config) #crypto isakmp key VPNKEY address XXX.XXX.XXX. XXX


where, VPNKEY is the shared key that you will use for the VPN, and remember to set the same key on the other end.

XXX.XXX.XXX. XXX the static public IP address of the other end.

3. Now we set lifetime for the IPSec security associations,

Router(config) #crypto ipsec security-associatio n lifetime seconds YYYYY

where YYYYY is the associations lifetime in seconds. It is usually used as 86400, which is one day.

4. Configure an extended access-list to define the traffic that is allowed to be directed through the VPN link,

Router(config) #access-list AAA permit ip SSS.SSS.SSS. SSS WIL.DCA.RDM. ASK DDD.DDD.DDD. DDD WIL.DCA.RDM. ASK


where,AAA is the access-list number

SSS.SSS.SSS. SSS WIL.DCA.RDM. ASK is the source of the data allowed to use the VPN link.

DDD.DDD.DDD. DDD WIL.DCA.RDM. ASK is the destination of the data that need to pass though the VPN link.

5. Define the transformations set that will be used for this VPN connection,

Router(config) #crypto ipsec transform-set SETNAME BBBB CCCCC


where, SETNAME is the name of the transformations set. You can choose any name you like.

BBBB and CCCCC is the transformation set. I recommend the use of “esp-3des esp-md5-hmac”. You can also use “esp-3des esp-sha-hmac”. Any one of these two will do the job.


6. After defining all the previous things, we need to create a cypto-map that associates the access-list to the other site and the transform set.

Router(config) #crypto map MAPNAME PRIORITY ipsec-isakmp

Router(config- crypto-map) #set peer XXX.XXX.XXX. XXX

Router(config- crypto-map) #set transform-set SETNAME

Router(config- crypto-map) #match address AAA


where,MAPNAME is a name of your choice to the crypto-map

PRIORITY is the priority of this map over other maps to the same destination. If this is your only crypto-map give it any number, for example 10.

XXX.XXX.XXX. XXX the static public IP address of the other end

SETNAME is the name of the transformations set that we configured in step 5

AAA is the number of the access-list that we created to define the traffic in step 4

7. The last step is to bind the crypto-map to the interface that connects the router to the other end.

Router(config- if)#crypto map MAPNAME

where MAPNAME is the name of the crypto-map that we defined in step 6.
Now, repeat these steps on the other end, and remember to use the same key along with the same authentication and transform set.

Note: If you want to implement multiple VPN connections to multiple sites, you can do this by repeating the steps 2 to 7 (except step 3) for each VPN connection. The different crypto-maps and their assignments differentiate between the different VPN connections.

For troubleshooting purposes, you can use the following commands,

show crypto isakmp sa

show crypto ipsec sa

show crypto engine connections active

and show crypto map



Tag: step by step site to site vpn, site to site vpn setup, site to site vpn configuration, how to setup a site to site vpn, command to setup site to site vpn