User Guide

80 Chapter 4. Configuring Special Features
The values for this option that have been set globally, specific to a subnetwork, or specific to a client will
not
be removed. The administrator must remove those values explicitly. Well-known type option codes
cannot
be
changed or deleted.
Configuring BootP/DHCP Relays
BootP/DHCP Relays are used by system administrators when the DHCP configuration parameters are acquired
from a BootP/DHCP server other than the router’s DHCP server.
This feature allows configuration information to be centrally controlled. Enabling a BootP/DHCP Relay disables
DHCP on the router since (by definition) only one policy mechanism can be supported.
BootP/DHCP Relays are enabled and disabled using the command:
system bootpserver
Other Information
DHCP information is kept in the file DHCP.DAT, a self-contained file.
This file contains
all
DHCP information including:
• the option definitions
• the subnetworks that have been added
• the client lease information
• the option values that have been set
This file can be uploaded/downloaded from one router to another.
Network Address Translation (NAT)
The router supports classic NAT (one NAT IP address assigned to one PC IP address) and a NAT technique
known as masquerading (one single NAT IP address assigned to many PC IP addresses).
General NAT Rules
1. IP routing must be enabled.
2. NAT can be run on a per-remote-router basis.
3. Any number of PCs on the LAN may be going to the same or different remote routers at the same time. In
reality, the number of PCs on the LAN that can be supported is limited by how much memory the router
consumes maintaining table information
and
by how many connections are currently active.
4. Some operations will
not
work. Specifically, services that place IP address/port information in the data
may
not work
until the router examines their packets and figures out what information in the data needs to be
changed. Remember that the router is remapping both IP addresses and ports.