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New Member

Site-To-Site VPN tunnel


I have configured VPN tunnel between branch office and central site (Cisco 876 and Cisco 2811 routers) and it's working fine.

Branch office has dynamic IP address from ADSL, and central office has static public IP address.

Question is: Is it possible to keep this VPN tunnel alive, even if there is no interesting traffic from branch office?

Sometimes, when there is no interesting traffic from remote site, the tunnel goes down, and in that case, if central site LAN user want to communicate with branch user, he cant't do that until branch user do ping or something else to establish a tunnel.



Re: Site-To-Site VPN tunnel


how did you specify the 800 router as peer in your crypto map ,since it has an ip address that is not garanted to be the same every time specificaly after a reboot or an expiration of the DHCP bail ???

New Member

Re: Site-To-Site VPN tunnel

"Central site"

crypto keyring spokes

pre-shared-key address key ****

crypto isakmp profile L2L

description LAN-TO-LAN for spoke router(s) connection

keyring spokes

match identity address

crypto ipsec transform-set rtpset esp-3des esp-md5-hmac

crypto dynamic-map rtpmap 10

set transform-set rtpset

set isakmp-profile L2L

crypto map clientmap 10 ipsec-isakmp dynamic rtpmap

interface Serial1/0:0


crypto map clientmap

So, with this configuration, any IP address with correct pre-share key will be accepted.

At Remote site, crypto map referencing to this static public IP address of central router.

And, becouse remote site has IP address which is periodically change, only that site can initiate VPN connection.

I just need some mechanism which will keep this VPN connection alive. (Simple, but irritating solution is to make batch file on one of the remote site host, which will periodically ping the other LAN's address)


Re: Site-To-Site VPN tunnel


Check that your router IOS supports DPD (Dead Peer Detection) also known as IKE Keepalives, take a look here for further explanation:

Hope this helps and please rate posts if it does!!


New Member

Re: Site-To-Site VPN tunnel

I already tried something with command

crypto isakmp keepalive 10 periodic

but with no success.

But, I'll try again, maybe I miss something.

Thanks for replay anyway.

Re: Site-To-Site VPN tunnel


Why not creating a standard site-to-site connection? You can do that if you your branches have static IP in the Internet.

If not, an elegant solution is to create GRE interfaces both on branch and hub and set the VPN between them. The "keepalive" option on the GRE interface will make sure the tunnel will never go down due to the lack of traffic.

Check GRE over IPSEC section.

If this helped, please rate.

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