SNR S2989G-48TX [215/553] Dhcp snooping

S2989G-24TX Operation Manual

Chapter 3 IP services Configuration

3-53

Now, the DHCP server will allocate addresses for the network nodes from Switch1

which are relayed by Switch3 within the range of 192.168.102.21 ~ 192.168.102.50, and

allocate addresses for the network nodes from Switch1 within the range of

192.168.102.51～192.168.102.80.

3.15.4

DHCP option 82 Troubleshooting

1. DHCP option 82 is implemented as a sub-function module of DHCP Relay Agent.

Before using it, users should make sure that the DHCP Relay Agent is configured

correctly.

2. DHCP option 82 needs the DHCP Relay Agent and the DHCP server cooperate to

finish the task of allocating IP addresses. The DHCP server should set allocating

policy correctly depending on the network topology of the DHCP Relay Agent, or,

even the Relay Agent can operate normally, the allocation of addresses will fail.

When there is more than one kind of Relay Agent, please pay attention to the

retransmitting policy of the interface DHCP request messages.

3. To implement the option 82 function of DHCP Relay Agent, the “debug dhcp relay

packet” command can be used during the operating procedure, including adding the

contents of option 82, the retransmitting policy adopted, the option 82 contents of the

server peeled by the Relay Agent and etc., such information can help users to do

troubleshooting.

4. To implement the option 82 function of DHCP server, the “debug ip dhcp server packet”

command can be used during the operating procedure to display the procedure of

data packets processing of the server, including displaying the identified option 82

information of the request message and the option 82 information returned by the

reply message.

3.16

DHCP Snooping

3.16.1

Introduction to DHCP Snooping

DHCP Snooping means that the switch monitors the IP-getting process of DHCP

CLIENT via DHCP protocol. It prevents DHCP attacks and illegal DHCP SERVER by

setting trust ports and untrust ports. And the DHCP messages from trust ports can be

forwarded without being verified. In typical settings, trust ports are used to connect DHCP