Saturday, March 26, 2005

A Perplexing Problem

I have been working on a VPN project for a health care customer for nearly two weeks. The local company is switching software and requires a VPN connection with the new company. We have traditionally used Sonicwall for our VPN/firewall units. After installing and configuring the Sonicwall, the VPN come up immediately but would not inniate from the other end. Before I could address this issue, the DSL circuit was moved and remained unstable for a number days.

The configuration involves a Qwest DSL circuit with an Actiontec modem/router. The Sonicwall sits behind the router, set to transparent mode. The Actiontec provides NAT services and passes the IPSEC information to the Sonicwall. The Sonicwall has a setting called NAT Traversal which allows it to route the VPN tunnel through another NAT device. Thus, a VPN between two Sonicwalls, or similar devices, is quite simple over the standard DSL circuit.

After several sessions and discussions with Sonicwall tech support, the situation did not change. The device on the other end was a Nortel Contivity 5000. No one at Sonicwall had any prior experience connecting to this device. Finally, the network tech at the other end realized that the Sonicwall on this end was behind a NAT device. He stated that to the best of his knowledge, the Nortel would not bring up a VPN through a NAT connection. The Sonicwall would have to have a true external IP.

The standard Qwest DSL connection in this area uses an Actiontec modem connecting with PPOa. This allows the Actiontec to forward a user name and password for authentication. The Actiontec has a public IP on the DSL side and a locally assigned private IP on the network side. The Sonicwall, in transparent mode, has another locally assigned IP on its WAN port.

To work correctly in the situation I was in, the Actiontec must be set in bridge mode so the public IP is assigned to the Sonicwall's WAN port. This prevents the Actiontec from passing a username/password to the ISP. The Sonicwall does not do PPOa, only PPOe. Consequently, the ISP has to configure the connection to authenticate in some other manner.

In this case, the ISP, Cybertrails, offered authentication with a dedicated IP. The connection was configured, I reset the Actiontec and Sonicwall, and up came the VPN.


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