Sorry to continue this non-firewall thread, but I hate to see incorrect
information being propagated....
Lance Ecklesdafer wrote:
>
> I am given to understand that NETBIOS is itself not a protocol at all.
Actually, this is incorrect. Developed by IBM for their PC Network LAN,
NetBIOS was created to be an application program interface (API).
NetBIOS is designed to be a front end for carrying out inter-application
communications. NetBIOS defines the interface to the network protocol,
not the protocol itself. At the time of development it was assumed that
the application accessing NetBIOS would assume responsibility for
defining the protocols required for transmitting the information. So
NetBIOS _is_ a communication protocol, it just has no layer 3 component.
NetBIOS also has a very loose specification for the presentation and
application layers. There is no standard structure or format specified.
This has lead to NetBIOS being paired with other protocols such as
NetBEUI, IPX and IP which can provide a precise specification. It has
also lead to incompatibility problems as vendors were left to create
proprietary implementations. Artisoft's LANtastic is a good example of a
system which communicates using a proprietary NetBIOS implementation and
is unable to communicate with other NetBIOS systems.
> NETBEUI is a very fast and efficient protocol, but it is not routable and
> does not scale. For a small network like most small offices and small
> businesses, this is one of the fastest protocols available.
Actually, I would disagree here as well. I spent quite a bit of time
taking traces and measuring protocol efficiency. IPX/NCP wins in this
arena with NFS coming in second. NetBEUI is no more efficient that
NetBIOS over IP, its just easier to configure.
> In order to be
> able to scale and support backwards compatibility along comes NBT. This
> protocol allows NETBIOS calls from workstations and servers to traverse a
> network with more than one physical segment.
By "NBT" do you mean NetBIOS over IP? If so, this actually came along
later. IBM formalized the transport framework of NetBIOS into NetBEUI
around 1985. After that, NetBIOS was run over IPX in order to traverse
network segments. The problem with NetBIOS over IPX is that the traffic
is broadcast based so it could quickly saturate a small to medium
network environment. Routers have to be configured to propagate these
broadcasts across multiple networks. In the Cisco world this is referred
to as "type 20 propagation" with is the decimal value of the "type"
number for this traffic.
Also, NetBIOS over IP is not backwards compatible as stated above. True
it uses the NetBIOS structure, but you will never get a NetBIOS over IP
system to communicate with a system talking straight NetBIOS.
> Layer 3 devices will forward NBT packets
Depends. Layer 3 devices will _not_ forward NetBIOS over IP name claim
or address resolution packets which are broadcast/multicast based. They
will forward datagram, but the hosts have to find each other first. This
is where using LMHOSTS or a NetBIOS Name Server (NBNS a la MS WINS)
comes into play. It eliminates the need for the broadcast portion of
NetBIOS over IP traffic.
> and you can also configure most layer 3 devices to forward
> broadcast traffic for functions like DHCP and WINS.
True with DHCP, not true with WINS. Remember that WINS requires that all
NetBIOS over IP hosts to be unicast based (p-node, h-node or m-node).
Since no broadcast/multicast traffic is being generated, there is no
broadcast traffic for the router to forward. This allows a layer 3
device to support NetBIOS over IP like any other IP protocol (Telnet,
HTTP, etc.) because all communications are unicast.
Cheers,
Chris
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