Reference Guide

Consider the following example:
OS10# show running-configuration interface ethernet 1/1/2
!
interface ethernet1/1/2
no shutdown
no switchport
ip address 100.1.1.1/24
flowcontrol receive off
OS10# show running-configuration ip dhcp
!
ip dhcp server
no disable
!
pool host1
host 100.1.1.34
hardware-address 00:0c:29:ee:4c:f4
!
pool hostnetwork
lease infinite
network 100.1.1.0/24
!
pool host2
host 20.1.1.34
hardware-address 00:0c:29:aa:22:f4
In this example, the pool ‘host1,” which is the fixed host mapping pool, inherits the subnet and other attributes from the pool,
“hostnetwork,” which is the DHCP client IP address pool. There is no matching network pool for "host2." Hence, the DHCP
client with the MAC address 00:0c:29:aa:22:f4 will not obtain the correct parameters.
DHCP relay agent
A DHCP relay agent relays DHCP messages to and from a remote DHCP server, even if the client and server are on different IP
networks. You can configure the IP address of the remote DHCP server.
You can configure a device either as a DHCP server or a DHCP relay agent — but not both.
The DHCP relay agent supports multi-virtual routing and forwarding (VRF) instances. The client-facing and server-facing
interfaces must be in the same VRF.
The DHCPv6 relay agent performs the same role as that of a DHCP relay agent, but in an IPv6 network. The DHCP relay
agent forwards the DHCPv4/DHCPv6 messages from the configured interface to the DHCPv6 server as a unicast message. The
DHCP relay agent then forwards the server’s response to the client.
When you configure DHCPv6 relay on an interface, you must:
● Configure an IPv6 address on the interface.
● Ensure that the DHCPv6 server is reachable.
Option 82 for security
DHCP, as defined by RFC 2131, provides no authentication or security mechanisms. To provide security, the DHCP relay agent
supports Option-82 with Circuit ID sub option, which is the printable name of the interface where the client request was
received.
This option secures all DHCP traffic that goes through a DHCP relay agent, and ensures that communication between the DHCP
relay agent and the DHCP server is not compromised.
The DHCP relay agent inserts Option 82 before forwarding DHCP packets to the DHCP server. The DHCP server includes
Option 82 back in its response to the relay agent. The relay agent uses this information to forward a reply out the interface on
which the request was received rather than flooding it on the entire VLAN. However, the relay agent removes Option 82 from
its DHCP responses before forwarding the responses to the client.
NOTE: Option 82 is supported, but not configurable.
System management 467