- Enterasys Security Router User's Guide

XSR User’s Guide 15-1
15
Configuring DHCP
Overview of DHCP
The Dynamic Host Configuration Protocol (DHCP) allocates and delivers configuration values,
including IP addresses, to Internet hosts. Consisting of two components, DHCP provides host-
specific configuration parameters from a DHCP Server to a host, and allocates network addresses
to hosts. Recent extensions to the DHCP protocol extends high-availability, authenticated and
QoS-dependent configuration of Internet hosts.
DHCP is based on the client-server model - a designated DHCP Server allocates network
addresses and delivers configuration values to dynamically configured clients. Throughout this
chapter, the term server refers to a host providing initialization values via DHCP, and the term
client refers to a host requesting initialization values from a DHCP Server.
The XSR’s DHCP Client implementation obtains IP addresses and configuration data for a router
interface rather than a PC host. Be aware that DHCP Client cannot be configured on an XSR
interface which already has a an IP address configured. Also, many capabilities and options
typically supported by DHCP Client - SMTP, POP3 Server, many Microsoft-related options - are
not supported. The Client silently ignores these options if it receives a DHCPOFFER /DHCPACK
containing such parameters. Also, although the reply packet may contain a bootfile and server
address field the DHCP Client will not initiate a TFTP file download in response to DHCPOFFER
or DHCPACK.
DHCP allocates IP addresses in two ways:
• Dynamic allocation assigns an IP address to a client for a limited interval - lease - (or until a
client explicitly relinquishes its address).
• Manual allocation involves a client IP address assigned by the network administrator, with
DHCP used simply to convey the assigned address to the client.
DHCP messages are formatted similar to BOOTP messages to capture BOOTP Relay Agent
behavior and allow existing BOOTP clients to interoperate with DHCP servers. DHCP is
backward compatible with BOOTP (RFC-951). Implemented as an improvement to BOOTP,
DHCP differs from BOOTP by its dynamically IP address allocation and lease definition
capabilities.
Features
The XSR offers the following DHCP features:
• Persistent storage/database of network values for network clients.
• Persistent storage of network client lease states kept across reboot.
• Temporary or permanent network (IP) address allocation to clients.
• Network configuration parameter assignment to clients.