Reference Guide

• 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.

DHCP Client on a VLAN

The following conditions apply on a VLAN that operates as a DHCP client:

• The default VLAN 1 with all ports auto-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.

DHCP Packet Format and Options

DHCP uses the user datagram protocol (UDP) as its transport protocol.

The server listens on port 67 and transmits to port 68; the client listens on port 68 and transmits to port

67. The configuration parameters are carried as options in the DHCP packet in Type, Length, Value (TLV)

format; many options are specified in RFC 2132. To limit the number of parameters that servers must

provide, hosts specify the parameters that they require, and the server sends only those parameters.

Some common options are shown in the following illustration.

Figure 6. DHCP packet Format

The following table lists common DHCP options.

Dynamic Host Configuration Protocol (DHCP)