Netbios over tcp/ip packet filter, Netbios name spoofing, Automatic configuration from bootp – Cisco 700 series User Manual

Page 4: Dhcp server

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1-4 Cisco 700 Series Router Installation Guide

Product Features

NetBIOS Over TCP/IP Packet Filter

A generic filter capability on the Transaction Control Protocol/User Datagram Protocol
(TCP/UDP) packets allows users to filter NetBIOS packets generated by application
programs. Use the set ip filter command to control this feature.

NetBIOS Name Spoofing

When a WINS client sends out a NetBIOS Name query, the router can answer a NetBIOS
name query in place of the WINS server. If the router cannot answer, the router forwards
the query packets to the server, which forwards the response to the client. If spoofing is set,
the router keeps a local database of up to 100 Domain Name System (DNS) name entries
and has an aging scheme to age out the unused name entries.

Automatic Configuration From BOOTP

The automatic configuration feature allows the Cisco 700 series router to obtain a
configuration file from a remote server using BOOTP protocol. Upon power-up, the router
examines the Auto_Config flag stored in NVRAM. If the Auto_Config flag is FALSE, the
router initiates a BOOTP request for an IP address from the BOOTP server. If the BOOTP
server finds a matching MAC address, the server returns an IP address and a configuration
file name. The router initiates TFTP to download a configuration file.

After successfully loading the configuration file, the router sets the Auto_Config flag to
TRUE in NVRAM. In subsequence power-up operations, if the Auto_Config is TRUE, the
router does not initiate BOOTP. The set default command resets the Auto_Config flag to

The automatic configuration feature only works on the Ethernet interface. If the router does
not receive a BOOTP response from the server within 5 seconds of the first BOOTP request,
the router gives up and the Internet Protocol (IP) information must be configured manually.

DHCP Server

DHCP automates IP addressing and reduces the number of IP addresses a site might
require. Cisco 700 series routers can function as a dynamic host configuration protocol
(DHCP) server. (The router can also act as a DHCP relay, but not both at the same time.)