Alcatel-Lucent 6850-48 ネットワークガイド

Setting Up the DHCP Server

Configuring Authenticated VLANs

page 36-30

OmniSwitch AOS Release 6 Network Configuration Guide

Normally, authentication clients cannot traffic in the default VLAN, so authentication clients do not 
belong to any VLAN when they connect to the switch. Even if DHCP relay is enabled, the DHCP discov-
ery process cannot take place. To address this issue, a DHCP gateway address must be configured so that 
the DHCP relay “knows” which router port address to use for serving initial IP addresses. (See 

 for information about configuring the gateway 

address.)

Note. The switch may be set up so that authentication clients will belong to the default VLAN prior to 
authentication (see 

). If a DHCP 

server is located in the default VLAN, clients may obtain initial IP addresses from this server without 
using a relay. However, the DHCP server is typically not located in a default VLAN because it is more 
difficult to manage from an authenticated part of the network. 

When the client authenticates, the client is moved into the allowed VLAN based on VLAN information 
sent from an authentication server (single mode authority) or based on VLAN information configured 
directly on the switch (multiple mode authority).

For information about authentication server authority modes, see 

After authentication a client may be moved into a VLAN in which the client’s current IP address does not 
correspond. This will happen if the DHCP gateway address for assigning initial IP addresses is the router 
port of an authenticated VLAN to which the client does not belong. (See 

.)

In this case, clients will send DHCP release/renew requests to get an address in the authenticated VLAN to 
which they have access; DHCP relay must be enabled so that the request can be forwarded to the appropri-
ate VLAN. 

Note. Telnet clients typically require manual configuration for IP address release/renew. Web browser 
clients will initiate their release/renew process automatically.

To enable DHCP relay, specify the DHCP server with the 

 command.

-> ip helper address 10.10.2.3

DHCP is automatically enabled on the switch whenever a DHCP server address is defined. For more infor-
mation about using the ip helper address command, see 

If multiple DHCP servers are used, one IP address must be configured for each server. The default VLAN 
DHCP gateway must also be specified so that Telnet and Web browser clients can obtain IP addresses 
prior to authentication. See the next section for more information.

If you want to specify that the relay only be used for packets coming in on an authenticated port, enter the 

 command.

-> ip helper avlan only