DHCP option 82 Configuration
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In the above example, layer 2 switches Switch1 and Switch2 are both connected to
layer 3 switch Switch3, Switch 3 will transmit the request message from DHCP client to
DHCP serer as DHCP Relay Agent. It will also transmit the reply message from the server
to DHCP client to finish the DHCP protocol procedure. If the DHCP option 82 is disabled,
DHCP server cannot distinguish that whether the DHCP client is from the network
connected to Switch1 or Switch2. So, all the PC terminals connected to Switch1 and
Switch2 will get addresses from the public address pool of the DHCP server. After the
DHCP option 82 function is enabled, since the Switch3 appends the port information of
accessing Switch3 to the request message from the client, the server can tell that whether
the client is from the network of Swich1 or Swich2, and thus can allocate separate
address spaces for the two networks, to simplify the management of networks.
The following is the configuration of Switch3(MAC address is 00:03:0f:02:33:01):
Switch3(Config)#service dhcp
Switch3(Config)#ip dhcp relay information option
Switch3(Config)#ip forward-protocol udp bootps
Switch3(Config)#interface vlan 3
Switch3(Config-if-vlan3)#ip address 192.168.10.222 255.255.255.0
Switch3(Config-if-vlan2)#ip address 192.168.102.2 255.255.255.0
Switch3(Config-if-vlan2)#ip helper 192.168.10.88
Linux ISC DHCP Server supports option 82, its configuration file /etc/dhcpd.con is
ddns-update-style interim;
ignore client-updates;
class "Switch3Vlan2Class1" {
match
if
option
agent.circuit-id
=
"Vlan2+Ethernet1/0/2"
and
option
agent.remote-id=00:03:0f:02:33:01;
}
class "Switch3Vlan2Class2" {
match
if
option
agent.circuit-id
=
"Vlan2+Ethernet1/0/3"
and
option
agent.remote-id=00:03:0f:02:33:01;
}
subnet 192.168.102.0 netmask 255.255.255.0 {
option routers 192.168.102.2;
option subnet-mask 255.255.255.0;