DHCP Option 82 And Classes In Depth Understanding

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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Received on Mon Oct 26 2009 - 12:19:14 ART