White Papers

You can override the DHCP-assigned address on the OOB management interface by manually configuring an IP address using
the CLI or CMC interface. If no user-configured IP address exists for the OOB interface exists and if the OOB IP address is
not in the startup configuration, the Aggregator will automatically obtain it using DHCP.
You can also manually configure an IP address for the VLAN 1 default management interface using the CLI. If no user-
configured IP address exists for the default VLAN management interface exists and if the default VLAN IP address is not in
the startup configuration, the Aggregator will automatically obtain it using DHCP.
● The default VLAN 1 with all ports configured as members is the only L3 interface on the Aggregator. When the default
management VLAN has a DHCP-assigned address and you reconfigure the default VLAN ID number, the Aggregator:
○ Sends a DHCP release to the DHCP server to release the IP address.
○ Sends a DHCP request to obtain a new IP address. The IP address assigned by the DHCP server is used for the new
default management VLAN.
How DHCP Client is Implemented
The Aggregator is enabled by default to receive DHCP server-assigned dynamic IP addresses on an interface. This setting
persists after a switch reboot. If you enter the shutdown command on the interface, DHCP transactions are stopped and the
dynamically-acquired IP address is saved. Use the show interface type slot/port command to display the dynamic IP
address and DHCP as the mode of IP address assignment. If you later enter the no shutdown command and the lease timer
for the dynamic IP address has expired, the IP address is unconfigured and the interface tries to acquire a new dynamic address
from DHCP server.
If you later enter the no shutdown command and the lease timer for the dynamic IP address has expired, the IP address is
released.
When you enter the release dhcp command, although the IP address that was dynamically-acquired from a DHCP server
is released from an interface, the ability to acquire a new DHCP server-assigned address remains in the running configuration
for the interface. To acquire a new IP address, enter either the renew dhcp command at the EXEC privilege level or the ip
address dhcp command at the interface configuration level.
If you enter renew dhcp command on an interface already configured with a dynamic IP address, the lease time of the
dynamically acquired IP address is renewed.
NOTE:
To verify the currently configured dynamic IP address on an interface, enter the show ip dhcp lease
command. The show running-configuration command output only displays ip address dhcp; the currently assigned
dynamic IP address is not displayed.
DHCP Client on a Management Interface
These conditions apply when you enable a management interface to operate as a DHCP client.
● The management default route is added with the gateway as the router IP address received in the DHCP ACK packet. It
is required to send and receive traffic to and from other subnets on the external network. The route is added irrespective
of whether the DHCP client and server are on same or different subnets. The management default route is deleted if the
management IP address is released like other DHCP client management routes.
● ip route for 0.0.0.0 takes precedence if it is present or added later.
● Management routes added by a DHCP client display with Route Source as DHCP in the show ip management route
and show ip management-route dynamic command output.
● Management routes added by DHCP are automatically reinstalled if you configure a static IP route with the ip route
command that replaces a management route added by the DHCP client. If you remove the statically configured IP route
using the no ip route command, the management route is reinstalled. Manually delete management routes added by the
DHCP client.
● To reinstall management routes added by the DHCP client that is removed or replaced by the same statically configured
management routes, release the DHCP IP address and renew it on the management interface.
● Management routes added by the DHCP client have higher precedence over the same statically configured management
route. Static routes are not removed from the running configuration if a dynamically acquired management route added by
the DHCP client overwrites a static management route.
● Management routes added by the DHCP client are not added to the running configuration.
NOTE:
Management routes added by the DHCP client include the specific routes to reach a DHCP server in a different
subnet and the management route.
256 Dynamic Host Configuration Protocol (DHCP)