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New Member

My first site to site VPN

Dear all

this is my first time to configure site to site vpn.

I have in site A (Cisco router 1801 which connected to Internet by leased line and LAN is

in site B (Cisco router 887va which connected with 4Mbps ADSL connection and LAN is

NOTICE **i use 887router as adsl modem do i will face any problem**

Do I need real IP in both sites?

the simplest way to configure  this vpn?

Best regard


Cisco Employee

My first site to site VPN

Hello Mahmoud,

As to your question, do you mean by "real IP" a static public IP for the outside interfaces of the routers?

Normally, in a L2L enviroment, you enter the public IPs in the configuration in order to negotiate a VPN tunnel between the 2 peers.

However, you can configure it so that 1 side uses a static public IP (leased line) while the other side uses a changing IP (DHCP assigned for example).

For the first senario, use the router configuration in the link below

For the second Scenario, Use the below suggestions

For Site A, use the router configuration in the link below.

The following commands need to be added instead of the ones in the link:

crypto ipsec transform-set myset esp-3des esp-sha-hmac
crypto ipsec security-association lifetime seconds 28800
crypto ipsec security-association lifetime kilobytes 4608000
crypto dynamic-map mydyn 10 set transform-set myset
crypto map mymap 65535 ipsec-isakmp dynamic mydyn
crypto map mymap interface outside


crypto isakmp key hostname

= Fully qualified domain name.

For Site B, use the same configuration as in the link but make the following changes:

crypto isakmp peer address 
set aggressive-mode password
set aggressive-mode client-endpoint fqdn
New Member

My first site to site VPN

Thank you zaid for your reply, I appreciate that

would you please tell me more about using one single static public ip in one site while the other is dynamically assigned by isp. this method has any disadvanteges as i need to connect lan to lan.

the above link you provided talk about private ip(s) only.

Cisco Employee

My first site to site VPN

In my previous post, I mentioned how you can change the configuration in the link to meet your needs. I don't believe there are any disadvantages.  Its just another way to set up L2L.

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