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dhcp snooping and option 82

Hi every body!

Here is what my book says:

" you can also configure the switch to use dhcp option 82, the dhcp relay agent information option,which is described in rfc 3046. when a dhcp request in intercepted on an untrusted port,the switch adds its own mac address and the switch port identifier into the option 82 feild of the request. The request then is forwarded normally so that it can reach a trusted dhcp server.

Adding option-82 provides more information about the actual client that generated the dhcp request.In addition, the dhcp reply(if any) echoes back the option082 information. the switch intercepts the reply and compares the option-82 data to confirm that the request came from a valid port on itself"

The above paragraph only says "the switch adds its own mac address and the switch port identifier into the option 82 feild of the request."

Then the second paragraph says"Adding option-82 provides more information about the actual client that generated the dhcp request"

the question is, switch has only added its info in option 82 ii did not add any info about the client that generated the dhcp request.

How does option 82 help in dhcp snoooping?

thanks a lot!

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Bronze

Re: dhcp snooping and option 82

The switch adds the information to the packet, not the client. The switch ONLY does this when "option 82" is enabled (configured) on the switch.

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Bronze

Re: dhcp snooping and option 82

I doesn't help in dhcp snooping itself as far as i am aware off. It simply adds the switch mac and port information into "option 82".

This information is meant for the DHCP server, not for the switch itself. that is why parag 2 says: the switch adds more information about the client, yes, it adds on which switch and on which port the client is connected.

The DHCP server can then assign a DHCP ip address based on the switchport ie. port one gets .1, port 2 gets .2 etc... (if your server supports this though !)

Bronze

Re: dhcp snooping and option 82

Thanks !

switch already adds its mac and port that received the dhcp request what client info it adds? if you say client info includes the port that received the dhcp req, and switch own mac, then they were already added in the option by switch.

Bronze

Re: dhcp snooping and option 82

The switch adds the information to the packet, not the client. The switch ONLY does this when "option 82" is enabled (configured) on the switch.

Bronze

Re: dhcp snooping and option 82

thanks for your reply1

But the book also says the switch adds client info in option 82 besides its own address and the port that received the request.

My question is what client info switch adds to option 82?

thanks

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