IP Routing Features
Configuring DHCP Relay
[ ip | mac ]
This option specifies the remote ID suboption the routing switch will use in
Option 82 fields added or appended to DHCP client packets. The choice of type
depends on how you want to define DHCP policy areas in the client requests
sent to the DHCP server. (Refer to "Option 82 Field Content" on page 5-81.)
ip: Specifies the IP address of the VLAN on which the client DHCP packet enters
mac: Specifies the routing switch's MAC address. (The MAC address used is
Notes on Default Remote ID Selection: Executing the Option 82 command
without specifying either ip or mac configures the remote ID as the MAC
address of the switch on which the packet was received from the client. The
command options for viewing the routing switch MAC address are listed at
the end of the "Remote ID" description that begins on page 5-81.
the same MAC address that is assigned to all VLANs configured on the
routing switch.) This is the default setting.
This implementation of DHCP relay with Option 82 complies with the
Moving a client to a different port allows the client to continue operating
as long as the port is a member of the same VLAN as the port through
which the client received its IP address. However, rebooting the client
after it moves to a different port can alter the IP addressing policy the
client receives if the DHCP server is configured to provide different
policies to clients accessing the network through different ports.
The IP address of the primary DHCP relay agent receiving a client request
packet is automatically added to the packet, and is identified as the giaddr
(gateway interface address). (That is, the giaddr is the IP address of the
VLAN on which the request packet was received from the client.) For
more information, refer to RFC 2131 and RFC 3046.
DHCP request packets from multiple DHCP clients on the same relay
agent port will be routed to the same DHCP server(s). Note that when
using 802.1X on a switch, a port's VLAN membership may be changed by
a RADIUS server responding to a client authentication request. In this case
the DHCP server(s) accessible from the port may change if the VLAN
assigned by the RADIUS server has different DHCP helper addresses than
the VLAN used by unauthenticated clients.