Cisco Systems OL-7426-03 Manual De Usuario

External DHCP Servers

The Operating System is designed to appear as a DHCP Relay to the network and as a DHCP Server to 
clients with industry-standard external DHCP Servers that support DHCP Relay. This means that each 
Cisco Wireless LAN Controller appears as a DHCP Relay agent to the DHCP Server. This also means that 
the Cisco Wireless LAN Controller appears as a DHCP Server at the virtual IP Address to wireless clients. 
Because the Cisco Wireless LAN Controller captures the client IP Address obtained from a DHCP Server, 
it maintains the same IP Address for that client during same-Cisco Wireless LAN Controller, inter-Cisco 
Wireless LAN Controller, and inter-subnet 

. 

Per-WLAN Assignment

All 

 can be configured to use the same or different DHCP Servers, or no 

DHCP Server. This allows operators considerable flexibility in configuring their Wireless LANs, as further 
described in the 

 section. 

Note that Cisco WLAN Solution WLANs that support 

 must allow the manage-

ment (device servicing) clients to obtain an IP Address from a DHCP Server.

Per-Interface Assignment

•

The Layer 2 

 can be configured for a primary and secondary DHCP 

server.

•

The Layer 3 

 can be configured for a primary and secondary DHCP server.

•

Each of the 

 can be configured for a primary and secondary DHCP 

server.

•

The 

 does not use DHCP servers.

•

The 

 can be configured to enable or disable DHCP servers.

Security Considerations

For enhanced security, it is recommended that operators require all clients to obtain their IP Addresses 
from a DHCP server. To enforce this requirement, all 

 can be configured 

with a ‘DHCP Required’ setting and a valid DHCP Server IP Address, which disallows client static IP 
Addresses. If a client associating with a WLAN with ‘DHCP Required’ set does not obtain its IP Address 
from the designated DHCP Server, it is not allowed access to any network services.
Note that if ‘DHCP Required’ is selected, clients must obtain an IP address via DHCP. Any client with a 
static IP address will not be allowed on the network. The Cisco Wireless LAN Controller monitors DHCP 
traffic since it acts as a DHCP proxy for the clients.
If slightly less security is tolerable, operators can create 

 with ‘DHCP 

Required’ disabled and a valid DHCP Server IP Address. Clients then have the option of using a static IP 
Address or obtaining an IP Address from the designated DHCP Server.
Operators are also allowed to create separate 

 with ‘DHCP Required’ 

disabled and a DHCP Server IP Address of 0.0.0.0. These WLANs drop all DHCP requests and force 
clients to use a static IP Address. Note that these WLANs do not support 

.