Re: DHCP Option 82 And Classes In Depth Understanding

Well ... looking at the guide, you can have the same subnet over two
separate vlans and the switch that forwards the DHCP requests has to have
the correct relay hex info that matches the class. This way the DHCP server
will know which class to serve the IP from. Same parent subnet, but
different IP ranges.

It does not appear that this can work on the same VLAN or same interface.
You have to have separate interfaces / vlans. I am not clear on the
interaction between the remote device (the relay) and the server.

It appears that the hex values have to match ... can you just make these
up? i do not know ...

I have a similar question as you ...

Here is the guide I googled / referenced:
http://www.ciscosystems.org.ro/en/US/docs/ios/12_3t/12_3t4/feature/guide/gdhcpopt.html

HTH,

Andrew lee Lissitz

On Tue, Oct 27, 2009 at 10:06 AM, karim jamali <karim.jamali_at_gmail.com>wrote:

> Hi,
>
> I didn't get any reply to my question up to this moment. I hope I will get.
>
>
> Best Regards,
>
> On Tue, Oct 27, 2009 at 4:52 PM, ALL From_NJ <all.from.nj_at_gmail.com>wrote:
>
>> Was there an answer to this? Just wanting to make sure I did not miss it
>> ...
>>
>>
>>
>> On Mon, Oct 26, 2009 at 5:19 AM, karim jamali <karim.jamali_at_gmail.com>wrote:
>>
>>> Dear Experts,
>>>
>>> I was reading through the DOC CD about DHCP Option 82, and the ability to
>>> create DHCP classes. Please correct me if I am wrong with the following
>>> statements:
>>>
>>> 1)DHCP request is a broadcasted on the LAN segment and it is up to the
>>> gateway (giaddress field) to convert it to a unicast ip address (relaying
>>> the information) when the ip helper-address is used pointing towards the
>>> server.
>>>
>>> 2)Based on this giaddress,the server knows that the client from a certain
>>> subnet requested an ip address, thus it provides it with an ip address
>>> from
>>> that subnet.
>>>
>>> 2)Option 82 gives another method to segregate clients other than the
>>> subnet
>>> in which users reside, i.e. having two hosts on a common vlan (subnet) it
>>> is
>>> still possible to give each host an ip address from a different range
>>> which
>>> corresponds to a different option 82 (hexadecimal value).This can happen
>>> by
>>> defining a common pool and dividing the pool into classes, where each
>>> class
>>> is matched by the option 82 value and corresponds to a different range of
>>> ip
>>> addresses.
>>>
>>> 3)The server will examine the relay agent information, and check it
>>> against
>>> the list of classes relay-information to find a match. This match will
>>> correspond to a certain class and a certain range of ip addresses within
>>> the
>>> pool.
>>>
>>> The part I don't understand is : Two users are on VLAN X for instance, I
>>> want to give each an ip address from a different range. I create two
>>> different classes each corresponding to a different range of ip addresses
>>> and to two different relay-information. Does the relay-information match
>>> the
>>> client-id?How is the client associated with a class?
>>>
>>>
>>> An example taken from DOC CD:
>>>
>>> Defines the DHCP classes and relay information patterns
>>>
>>> ip dhcp class CLASS1
>>>
>>> relay agent information
>>>
>>> relay-information hex 01030a0b0c02050000000123
>>>
>>> relay-information hex 01030a0b0c02*
>>>
>>> relay-information hex 01030a0b0c02050000000000 bitmask
>>> 0000000000000000000000FF
>>>
>>>
>>> ip dhcp class CLASS2
>>>
>>> relay agent information
>>>
>>> relay-information hex 01040102030402020102
>>>
>>> relay-information hex 01040101030402020102
>>>
>>>
>>> ip dhcp class CLASS3
>>>
>>> relay agent information
>>>
>>>
>>> ! Associates the DHCP pool with DHCP classes
>>>
>>> ip dhcp pool ABC
>>>
>>> network 10.0.20.0 255.255.255.0
>>>
>>> class CLASS1
>>>
>>> address range 10.0.20.1 10.0.20.100
>>>
>>> class CLASS2
>>>
>>> address range 10.0.20.101 10.0.20.200
>>>
>>> class CLASS3
>>>
>>> address range 10.0.20.201 10.0.20.254
>>>
>>>
>>>
>>> Thank You
>>>
>>> Best Regards,
>>>
>>>
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>>>
>>>
>>
>>
>> --
>> Andrew Lee Lissitz
>> all.from.nj_at_gmail.com
>>
>
>
>
> --
> KJ
>

-- 
Andrew Lee Lissitz
all.from.nj_at_gmail.com
Blogs and organic groups at http://www.ccie.net