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Configure NetBIOS Support
Configuring Source-Route Bridging BC-123
Configure NetBIOS Support
NetBIOS is a nonroutable protocol that was originally designed to transmit messages between
stations, typically IBM PCs, on a Token Ring network. NetBIOS allows messages to be exchanged
between the stations using a name rather than a station address. Each station knows its name and is
responsible for knowing the names of other stations on the network.
Note In addition to this type of NetBIOS, which runs over LLC2, we have implemented another
type of NetBIOS that runs over IPX. For information on the IPX type of NetBIOS, refer to the
chapter “Configuring Novell IPX” in the Network Protocols Configuration Guide, Part 2.
NetBIOS name caching allows the Cisco IOS software to maintain a cache of NetBIOS names,
which avoids the high overhead of transmitting many of the broadcasts used between client and
server NetBIOS PCs (IBM PCs or PS/2s) in an SRB environment.
When NetBIOS name caching is enabled, the software performs the following actions:
• Notices when any hosts send a series of duplicated “query” frames and reduces them to one frame
per period. The time period is configurable.
• Keeps a cache of mappings between NetBIOS server and client names and their MAC addresses.
By watching NAME_QUERY and NAME_RECOGNIZED request and response traffic between
clients and servers, the Cisco IOS software can forward broadcast requests sent by clients to find
servers (and by servers in reply to their clients) directly to their needed destinations, rather than
forwarding them for broadcast across the entire bridged network.
The software will time out the entries in the NetBIOS name cache after a specific interval of their
initial storage. The timeout value is a user-configurable value. You can configure the timeout value
for a particular Token Ring if the NetBIOS name cache is enabled on the interface connecting to that
Token Ring. In addition, you can configure static name cache entries that never time out for
frequently accessed servers whose locations or paths typically do not change. Static RIF entries are
also specified for such hosts.
Generally, NetBIOS name caching is most useful when a large amount of NetBIOS broadcast traffic
creates bottlenecks on WAN media connecting distant locations, and the WAN media is
overwhelmed with this traffic. However, when two high-speed LAN segments are directly
interconnected, the packet savings of NetBIOS name caching is probably not worth the processor
overhead associated with it.
Note NetBIOS name caching is not recommended to be turned on in backbone routers, particularly
if you have it enabled in all the routers connected to the backbone. NetBIOS caching should be
distributed among multiple routers. NetBIOS name caching can be used only between Cisco routers
that are running Software Release 9.1 or later.
To enable NetBIOS name caching, you must perform the tasks in the following sections:
• Enable the Proxy Explorers Feature on the Appropriate Interface
• Specify Timeout and Enable NetBIOS Name Caching
In addition, you can configure NetBIOS name caching as described in the following sections:
• Configure the NetBIOS Cache Name Length
• Enable NetBIOS Proxying