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Cisco VPN client and dynamic DNS


Does somebody know how to enable dynamic DNS (w2k workstation with VPN client to vpn3030 ) ?

The problem is that the client register ok with Wins but never with dns ( it stays as old IP address record) so some servers refuse to work.

I tried several version of client, manual dns registration and nothing

Thanks a lot

Cisco Employee

Re: Cisco VPN client and dynamic DNS

For DDNS to work, the 3030 has to get it's IP addresses from a DHCP server that is also a DDNS server, Win2K servers support this functionality.

In client v3.6 and above, during initial tunnel negotiation it includes its hostname, and the concentrator will send this hostname in the DHCP request packet to the internal DHCP server. It is then up to the DHCP/DDNS server to add this into it's tables, etc.

In reality, there's no configuration required on the client, and the only thing you need on the concentrator is to have it get the IP addresses from a DHCP server rather than from an internal pool. The DHCP server needs to do the rest.

New Member

Re: Cisco VPN client and dynamic DNS

Thanks a lot,

But this aplies to clients which don't support ddns (Win NT, 98)?

The W2k workstation is able to do it by itself even without DHCP.

But this is not working throught VPN.

Any idea?

Cisco Employee

Re: Cisco VPN client and dynamic DNS

As I said, VPN clients v3.6 and higher include their local hostname in the initial tunnel negotiation. If the concentrator is configured to get the IP address for this client from a DHCP server, it will include that hostname in the DHCP request. This is all the VPN client and the VPN concentrator do in this matter, nothing else.

It is up to the DHCP/DDNS server that receives the DHCP request from the concentrator to then add this hostname into it's DDNS tables. It has nothing to do with Windows NT or 98 as opposed to 2000, since all the VPN clients include their hostnames in the tunnel negotiation and this is where the DDNS server eventually picks it up from. I doubt the 2K workstation is able to add its VPN address into the DDNS server without using DHCP since the underlying Windows OS doesn't know anything about the VPN negotiated address (do an "ipconfig /all" and you won't see this address anywhere).

To repeat, it is not the Windows OS or the PC that adds its name into the DDNS server, it is a function of the VPN client sending the hostname to the concentrator, and the concentrator forwarding it to the DDNS server that gets it added in.

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