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18-2
Cisco ASA 5500 Series Configuration Guide using ASDM
Chapter 18 Configuring DHCP
Guidelines and Limitations
Note By default, the ASA 5505 ships with a 10-user license.
Guidelines and Limitations
Use the following guidelines to configure the DHCP server:
• You can configure a DHCP server on each interface of the ASA. Each interface can have its own
pool of addresses to draw from. However the other DHCP settings, such as DNS servers, domain
name, options, ping timeout, and WINS servers, are configured globally and used by the DHCP
server on all interfaces.
• You cannot configure a DHCP client or DHCP relay services on an interface on which the server is
enabled. Additionally, DHCP clients must be directly connected to the interface on which the server
is enabled.
• The ASA does not support QIP DHCP servers for use with DHCP proxy.
• The relay agent cannot be enabled if the DHCP server is also enabled.
• When it receives a DHCP request, the ASA sends a discovery message to the DHCP server. This
message includes the IP address (within a subnetwork) configured with the dhcp-network-scope
command in the group policy. If the server has an address pool that falls within that subnetwork, the
server sends the offer message with the pool information to the IP address—not to the source IP
address of the discovery message.
• For example, if the server has a pool in the range of 209.165.200.225 to 209.165.200.254, mask
255.255.255.0, and the IP address specified by the dhcp-network-scope command is
209.165.200.1, the server sends that pool in the offer message to the ASA.
Failover Guidelines
Supports Active/Active and Active/Standby failover.
Firewall Mode Guidelines
Supported in routed and transparent firewall modes.
Context Mode Guidelines
Supported in single mode and multiple context mode.
Configuring DHCP Relay Services
The DHCP Relay pane lets you configure DHCP relay services on the ASA. DHCP relay passes DHCP
requests received on one interface to an external DHCP server located behind a different interface. To
configure DHCP relay, you must specify at least one DHCP relay global server and then enable a DHCP
relay agent on the interface that receives DHCP requests.
This section includes the following topics:
• Editing DHCP Relay Agent Settings, page 18-4
• Adding or Editing Global DHCP Relay Server Settings, page 18-4