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272 Chapter 8: AppleTalk
NetBIOS Protocol
NetBIOS was created by IBM to interface with IBM LAN Server, Microsoft LAN Manager,
and OS/2. Microsoft Windows uses NetBIOS for all of its operations. When a client connects
to Network Neighborhood, NetBIOS makes access to the remote printer, client, or server
possible. When it was initially designed, no one could have known that NetBIOS might be used
beyond a local LAN. Therefore, NetBIOS has no Layer 3 addressing components and is not
routable. NetBIOS relies on Layer 2 broadcasts to communicate. To get from Point A to Point
B, NetBIOS must be transported across the network.
NetBIOS operates with a couple of other protocols quite nicely. NetBEUI, IPX, and TCP/IP all
support NetBIOS transport. For IPX, the NWLink protocol encapsulates NetBIOS. For
TCP/IP, NetBIOS over TCP/IP can be used.
NetBEUI Protocol
NetBEUI is a transport layer protocol. It uses the data-link layer to broadcast its requests to its
clients. Once the default protocol of Windows NT in the early days of its development,
NetBEUI is now a bench player at best. NetBEUI is the least scalable of the three protocols
(NetBEUI, NWLink, and TCP/IP) because it must be bridged. NetBEUI is included only to
support very old services, such as old versions of LAN Manager.
NetBEUI does not require any client address configuration. There is no fixed limit to the
number of Windows clients you can have with NetBEUI, but it is common for this solution to
run into performance problems as the number of clients in a single bridge group goes above 50
to 100 users. The flat topology and reliance on broadcasts do not scale, especially when traffic
must traverse a WAN link.
For only the smallest of LANs, like the home-area network (HAN), and for legacy network
operating systems still have value. Its main drawback is that it has no Layer 3 protocol and
cannot be routed.
NWLink Protocol
NetBIOS over IPX is NWLink. NWLink is recommended only for networks already running
IPX that cannot be upgraded to use TCP/IP. NWLink requires no client address configuration.
NWLink uses IPX type-20 packets to exchange registration and browsing information. To
forward type-20 IPX packets across Cisco routers, configure ipx type-20 propagation on each
interface on every router on your network.
87200333.book Page 272 Wednesday, August 22, 2001 2:37 PM