SNR S2989G-24TX-UPS [213/553] Dhcp option 82 application examples
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SNR S2989G-24TX-UPS [213/553] Dhcp option 82 application examples

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SNR S2989G-8TX-POE [213/553] Dhcp option 82 application examples
S2989G-24TX Operation Manual
Chapter 3 IP services Configuration
3-51
show ip dhcp relay information option
This command will display the state
information of the DHCP option 82 in the
system, including option82 enabling
switch, the interface retransmitting policy,
the circuit ID mode and the DHCP server
option82 enabling switch.
debug ip dhcp relay packet
This command is used to display the
information of data packets processing in
DHCP Relay Agent, including the “add”
and “peel” action of option 82.
3.15.3
DHCP option 82 Application Examples
DHCP Relay Agent
DHCP Client PC1
Switch1
Vlan2:ethernet1/0/3
Switch3
Vlan3
DHCP Client PC2
Switch2
Vlan2:ethernet1/0/2
DHCP Server
Figure 3-13 A DHCP option 82 typical application example
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

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