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Daryl uses Mozy for his online backups. |
The four items you need to use IP effectively on the Internet (that you don't need to set up an IPX workstation) are the IP Address, the IP Subnet Mask, the IP Address of the Default Router, and the IP Address(es) of your Domain Name Servers (DNS Servers, often shortened to "Name Servers.")
IP Addresses: IP uses 4-byte addresses, like 192.168.1.1. IPX uses 10-byte addresses, like 10000001:0000C04C1141. Those happen to be the IP and IPX addresses of the workstation I'm using now. "But wait," you ask, "I've used IPX before and all it uses are four byte addresses." Well, that's not entirely correct. The 4-byte "IPX Address" configured into IPX-based servers is only the network portion of the address. All addresses used by routable protocols have a "network" portion, which gets your packet to your nearest router, and a "host" portion, which indicates which host station you are on that routed segment. The 4-byte "IPX Address" you define is actually a 4-byte "IPX Network Address." The other 6 bytes is the hardware address of your NIC. Since IP addresses don't use the unique hardware address of your NIC, you must define them manually (or semi-manually by configuring a BOOTP or DHCP server, a task which is currently outside the scope of this document.)
IP Subnet Masks: Subnet masks (described in more detail in the next section) are used in IP to determine which part of the four-byte IP address describes the network you're on, and which part describes which host you are on that network segment. In IPX, the first four bytes always indicate the network you're on, and your six byte MAC layer address indicates which host you are on the network segment. In IP, the portions used to describe which network you're on can range from the first 8 bits of the address, to including all except the last two bits of the whole address. More in the next section.
Default Router: In IPX, routers are identified by sending out a broadcast that says, in essence, "Hey? Who out here is a router?" In IP, there has historically NOT been any automatic method for router discovery. There is now a protocol for IP router discovery, but it is not widely implemented. Therefore, you must tell the workstation what the address of the local router is. Note that with end-station PPP (like Win95 Dial-Up Networking), the default route is automatically set to, "out the serial cable." You do not need to set more than one default route. If the default router feels the packet would reach a destination better through a different router, the default router will tell your IP stack to use the other router (this is an ICMP Redirect.) If you specify no default route, no packets from that workstation can make it off the local wire; therefore, it is better to set a wrong default route than no default route. If in doubt, set the default route to the address of any known router on the local subnet.
DNS: In IPX, designed by Novell, the names (and corresponding addresses) of ALL services available on the network are stored in ALL Netware servers as a SAP table (SAP stands for Service Advertising Protocol.) Netware servers will share SAP information with each other automatically. Unfortunately, since ALL servers must know about ALL services, SAP tables can get very unwieldy on large networks, and without the benefit of advanced routing/advertising algorithms (NLSP), can flood networks with SAP broadcasts. The way IP handles name-to-address translation is called DNS. When you query your DNS server for a given name's address (such as www.novell.com), the DNS server will query one of the "root" servers for .COM. The root server tells the DNS server the address of the "authoritative" DNS server for novell.com. Your DNS server then asks the DNS server of novell.com what the address of www.novell.com is; when novell.com's DNS ponies up the address of www.novell.com, your local DNS "remembers" where www.novell.com was, so it doesn't have to look again the next time someone asks for that name's address. Note that DNS uses special records for mail routing, called MX records, that usually differ from the host addresses. Therefore, an ftp (or www, or gopher,...) connection to microsoft.com probably reaches a different address than mail sent to somebody@microsoft.com. Of course, the giveaway that you're talking mail ("MX" record) addresses, rather than host ("A" record) addresses, is the "@" in the address. Host names never have @ symbols, which is why you connect to www.microsoft.com, never www@microsoft.com.
BOOTP and DHCP: BOOTP was designed to ease the configuration of
desktop IP stacks. In a nutshell, a BOOTP-enabled workstation
sends out a broadcast BOOTP request, which is answered by a BOOTP
server. The answer includes workstation address, subnet mask,
default route, and DNS location(s). DHCP is generally accepted
as the "next generation" of BOOTP. Whereas BOOTP statically
assigns IP addresses by MAC address, DHCP supports address "leasing"
where an address is granted to a specific MAC address for a finite
amount of time, and can be reused after a specified amount of
time. DHCP also supports fields beyond BOOTP, most notably returning
information about the location of WINS server to Windows NT clients,
and the location of DSS servers to Netware/IP clients. (A DHCP
service is included with NT, and is available for free download
as part of the Netware/IP upgrade for Netware 4.10 servers, see
http://support.novell.com.)
Next: IP Addresses, Subnet Masks, and Subnetting