New Routing Features
Although you might think of Routing and Remote Access primarily as a service that provides dial-up access to remote users, the service's routing functionality is also important. Routing and Remote Access, like its NT 4.0 RRAS cousin, provides Win2K servers with a relatively full-featured software-based router that you can use for several purposes.
One of the most notable routing features in Routing and Remote Access is NAT support. NAT—which Internet Engineering Task Force (IETF) Request for Comments (RFC) 1631 defines—is similar to the ICS feature that Win2K Server, Win2K Pro, Windows Millennium Edition (Windows Me), and Windows 98 Second Edition (Win98SE) support. Like ICS, NAT translates private, nonroutable internal IP addresses into routable, Internet-connected addresses on the NAT-enabled server, thereby letting you share one machine's Internet connection with the entire network. However, only Win2K Server supports NAT, implementing it as an installable routing protocol under Routing and Remote Access.
You can use the Routing and Remote Access Server Setup Wizard's Internet connection server option to install NAT. Alternatively, after the wizard finishes, you can manually install NAT from the Routing and Remote Access management console. Simply right-click the General option under IP Routing, choose New Routing Protocol, and select Network Address Translation (NAT) from the list of choices, as Figure 3 shows.
After you install NAT, you need to identify the internal (i.e., LAN) adapter and external (i.e., Internet) adapters on the server. To do so, right-click each adapter, select Properties, and in the resulting dialog box, choose the appropriate option: Private interface to be connected to the private network or Public interface connected to the Internet. (Be sure to perform this step for both adapters.) This procedure lets the server distinguish between interfaces and enables proper function of NAT.
NAT offers several significant advantages over ICS. First, NAT lets you use your Routing and Remote Access server as a WINS server proxy agent—as well as a DNS server proxy agent—for NAT clients. This feature lets you pass name-resolution requests to a WINS server on behalf of LAN clients. (However, clients can't use this proxy to register in the WINS database; clients can only resolve names.) NAT offers greater flexibility than ICS in terms of the IP addresses that you can use on the internal LAN. (ICS supports an IP numbering scheme of 192.168.x.x on the internal LAN and forces the assignment of the address 192.168.0.1 to the ICS server.) Also, NAT supports multiple public IP addresses (ICS supports only one) and can successfully translate and support client protocols such as PPTP (which ICS can't). Finally, unlike ICS, NAT lets you make services on the internal LAN (e.g., Web servers or FTP servers) accessible to Internet-based clients.
If you chose the wizard's Internet connection server option, Routing and Remote Access automatically takes you through the process of installing and configuring NAT. The wizard installs NAT, then asks you to identify your LAN and Internet adapters. If necessary, you can also use the wizard to set up a dial-on-demand connection to your ISP as the NAT Internet connection. If you're not in a domain environment, the wizard asks you whether you want to set up a simple ICS connection rather than NAT. For a comparison of ICS and NAT features, see Table 1, page 54 For more information about ICS and NAT, see "Related Articles in Previous Issues," page 54.
Another new, but lesser known, addition to Routing and Remote Access is its Internet Group Management Protocol (IGMP) support. IP hosts use IGMP to report their IP multicast group memberships to IGMP-enabled routers. Routing and Remote Access includes IGMP router and proxy components. Whereas the IGMP router tracks multicast group membership for LAN clients on the same network as the IGMP router-enabled interface, the IGMP proxy component sends IGMP group membership packets from one interface on the server (although multiple IGMP router-enabled interfaces might exist). IGMP's primary purpose is to let LAN clients run IP multicast applications—a technology that's rapidly gaining popularity because of its increased efficiency for streaming high-bandwidth data to multiple network clients.
On the Routing and Remote Access server, you can enable or disable IGMP router and proxy support on a per-interface basis on the server; however, you can enable IGMP proxy support on only one adapter. To add IGMP router or proxy support, select IGMP from the IP Routing section of the Routing and Remote Access management console's left pane. Choose New Interface from the Action menu or the context menu that appears when you right-click IGMP.
You'll also need to set up one or more IP multicast address scopes on your server. IP multicast addresses exist in the range from 239.0.0.0 to 239.254.255.255. In the Routing and Remote Access management console's IP Routing\General section, you configure the addresses as one or more scopes on the Properties dialog box's Multicast Scopes tab. In addition to its new NAT and IGMP routing protocol support, Routing and Remote Access still supports the dynamic routing protocols Open Shortest Path First (OSPF) and Routing Information Protocol version 2 (RIP2), which NT 4.0 RRAS introduced.
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