NETGEAR RH348 ISDN Router

Connect your small network to the Internet

Small office/home office (SOHO) users have found that Basic Rate Interface (BRI) ISDN links provide the best method for connecting to corporate offices or the Internet. NETGEAR offers a device for making these connections—the NETGEAR RH348 ISDN Router, which incorporates support for BRI ISDN.

The RH348's FirstGear configuration utility makes installation easy. Because the RH348 can act as a DHCP server, you can set up the router by installing FirstGear on a PC, connecting the PC to one of the device's four hub ports, setting the PC's TCP/IP stack for configuration via DHCP, and rebooting the PC. FirstGear locates the router and lets you choose between the Quick and Advanced configuration methods. I chose the Quick configuration. I supplied phone numbers and Service Profile Identifiers (SPIDs) for the ISDN line, my user ID, and my password. I also enabled Network Address Translation (NAT) and DHCP Server services by selecting the check boxes for Fixed Address NAT and DHCP. I entered the fixed IP address my ISP supplied, and FirstGear swiftly connected me to my ISP.

Next, I configured FirstGear's Bandwidth-on-Demand feature. When you use this feature, the router makes an initial connection with one B channel. When traffic across the ISDN line reaches the rate you specify, the router dials and connects with a second B channel. When the traffic rate decreases, the router drops the second B channel. You can set the router to always use both B channels, but the Bandwidth-on-Demand feature can be useful, particularly for a home office. For example, if you are paying for connection time by channel, you can save money by using the second B channel for standard telephone service.

You set the Bandwidth-on-Demand options under the ISP configuration tab in FirstGear's Advanced configuration mode. I set the second B channel to activate after an average traffic rate of 40Kbps lasts 5 seconds, and to drop after an average traffic rate of 32Kbps lasts 20 seconds. Because the ISDN connection completes quickly, I also reduced the idle timeout for complete disconnection from the default of 5 minutes to 1 minute. I tested this configuration by initiating a file transfer. The second B channel connected when I expected, but took about 10 seconds longer than I specified to drop.

The RH348 supports standard packet filtering and call filters, which prevent certain types of packets from calling the ISP. The FirstGear GUI doesn't support configuring filters. Instead, you must use the built-in character-based menu system, connecting via Telnet or through the serial port on the back of the router. You can configure up to 12 sets of filters and list up to six protocol-and-port combinations for each filter. After you define filter sets, you can apply a set as a call filter, an input packet filter, or an output packet filter. You can specify up to four filter sets, for a total of 24 filtering rules, in each filter category. You can also define generic filters and specify the offset, length, mask, and value within the packet that the filter will look for. Unfortunately, this power and flexibility comes at the expense of ease of use.

I tested the RH348's ability to filter packets that support file access to an NT server. I used Systems Management Server (SMS) Network Monitor to show that NT connects to TCP port 139 on the target server, the NetBIOS session port. I set a filter to forward established packets and to filter out packets going to TCP port 139. When I applied the filter as an output filter, it successfully blocked access to servers on the far side of the router. When I applied the filter as an input filter, I could successfully access the outside servers. You can use an input filter to block NetBIOS sessions originating on the far side of the router, which is useful when you don't configure NAT on the router.

The RH348 has an ample feature set. And, aside from the packet filtering options, the router is easy to configure.