Dhcp And The Omniswitch; Dhcp Relay And Authentication; External Dhcp Relay Application - Alcatel OmniSwitch 6800 Series Network Configuration Manual

Configuring DHCP Relay

DHCP and the OmniSwitch

The unique characteristics of the DHCP protocol require a good plan before setting up the switch in a
DHCP environment. Since DHCP clients initially have no IP address, placement of these clients in a
VLAN is hard to determine. In simple networks (e.g., one VLAN) rules do not need to be deployed to
support the BOOTP/DHCP relay functionality.
In multiple VLAN network configurations, VLAN rules can be deployed to strategically support the
processing and relay of DHCP packets. The most commonly used rules for this function are IP protocol
rules, IP network address rules, and DHCP rules. All of these classify packets received on mobile ports
based on the packet protocol type, source IP address, or if the packet is a DHCP request. See
"Defining VLAN Rules,"

DHCP Relay and Authentication

Authentication clients may use DHCP to get an IP address. For Telnet authentication clients, an IP address
is required for authentication. The DHCP server may be located in the default VLAN, an authenticated
VLAN, or both. If authentication clients will be getting an IP address from a DHCP server located in an
authenticated VLAN, DHCP relay can handle DHCP requests/responses for these clients as well.
There are three relay forwarding options: standard, AVLAN only, and per-VLAN. All three support
DHCP traffic to/from authenticated clients. However, the AVLAN only option specifies that only DHCP
packets received on authenticated ports are processed. See
page 15-10 for more information.
Using DHCP Relay with authenticated VLANs and clients also requires relay configuration of the router
port address of the authenticated VLAN. See
information about this procedure.

External DHCP Relay Application

The DHCP Relay may be configured on a router that is external to the switch. In this application example
the switched network has a single VLAN configured with multiple segments. All of the network hosts are
DHCP-ready, meaning they obtain their network address from the DHCP server. The DHCP server resides
behind an external network router, which supports the DHCP Relay functionality.
One requirement for routing DHCP frames is that the router must support DHCP Relay functionality to be
able to forward DHCP frames. In this example, DHCP Relay is supported within an external router, which
forwards request frames from the incoming router port to the outgoing router port attached to the
OmniSwitch.
OmniSwitch 6800 Series Network Configuration Guide
for more information.
Chapter 18, "Configuring Authenticated VLANs,"
November 2004
"Setting the Relay Forwarding Option" on
DHCP Relay Overview
Chapter 7,
for more
page 15-5