DHCP Client identifier !!

[Murad*]

Hi

i have router and i want to configure DHCP server on it , with client identifier to detect PC connected with this router ,

my miss-config here is when i create ip dhcp poll , and then create(sub)

ip dhcp pool with client identifier , what is the relation between them ? and how i can force this PC to take IP automatically from sub-pool not from global poll ? and what is the command that use in router ? 

many thanks 

[balaji.bandi]

If i understand correctly your question.

you want to to reserve some IP address (here you calling as global - this should not allocate IP address to any one)

you creating the Pool of address for the user/Device ( you calling this as sub pool)

if this is correct then here is example for you :

example.

ip dhcp excluded-address 192.168.10.254

ip dhcp excluded-address 192.168.10.1 192.168.10.20   <--- this will exclude 1-20 ip address range



So from .20 to 253 available  for users/Devices from pool




ip dhcp pool your-pool
  network 192.168.10.0 255.255.255.0
  default-router 192.168.10.254




then configured client-identifier unique-identifier

[Georg Pauwen]

Hello,

the client takes the address from the pool whose default router IP address matches that of the subinterface the client is connected to. Post the config of your router so we can point you to the right settings...

[Richard Burts]

If I am understanding the original post correctly the intent is to have a DHCP pool used by most devices and to have a specific IP reserved for a single specific PC. I believe that the original poster is thinking of this as a global pool and then a sub pool. But that is not how it really works. What will accomplish this is to configure two pools. One will be the "global" pool with multiple addresses and will be used by most of the devices. Then there will be a second DHCP pool which has a single address in it and this is where the client identifier is used. (of course the address used in the second pool should be excluded from the first pool)

If there is something that I do not understand correctly then please provide clarification.

HTH

Rick

[Murad*]

[Deepak Kumar]

Hi,

As I getting you to want to know about DHCP static binding on the Cisco IOS. This is not a sub DHCP Pool (the Technical name is not correct).

Whenever a DHCP client sends a DHCP discover packet it will include its client identifier or MAC address. We can see this if we enable a debug on the DHCP server "debug ip dhcp server packet". The Cisco Router check the Discovery MAC-Address or Client identifier (Option 61) on the packet and if this mac-address or Identifier configured (binded) with a static IP in a dhcp pool then router will offer that bind IP to the system.

Configuration:

1. First Configure a DHCP Pool (Global Scope)

ip dhcp pool data
   network 192.168.5.0 255.255.255.0
   default-router 192.168.5.1 
   dns-server xxx.xxx.xxx.x xxx.xxx.xxx.x 
   lease 8

2. Now configure static binding:

IP dhcp pool MLGW
   host 192.168.5.10 255.255.255.0
   client-identifier 0100.04f3.0158.b3

Reset other details as Default gateway, DNS server, Domain name it will take from the globle pool.

DHCP clients require client identifiers. You can specify the unique identifier for the client in either of the following ways:

• A 7-byte dotted hexadecimal notation. For example, 01100.04f3.0158.b3, where 01 represents the Ethernet media type and the remaining bytes represent the MAC address of the DHCP client.
•  27-byte dotted hexadecimal notation. For example, 7665.6e64.6f72.2d30.3032.342e.3937.6230.2e33.3734.312d.4661.302f.31. The equivalent ASCII string for this hexadecimal value is vendor-0024.97b0.3741, where vendor represents the vendor, 0024.97b0.3741 represents the MAC address of the source interface.

Note:

If you put the address in the excluded addresses and in a manual binding scope your system won't get ip address.

Regards,

Deepak Kumar

[Murad*]

is this config true ?? 

[Deepak Kumar]

Hi,

Everything is looking good except to Client-Identifier address in the DHCP Pool.

As it is connected using Ethernet media then you have to add 01 before the MAC Address as

Client identifier 01aa.aabb.bbcc.cc

Regards,

Deepak Kumar

[Murad*]

did you mean i must adding (01) manually to the mac address ?!

[Deepak Kumar · Accepted solution]

Hi,
Yes. You are correct.

Regards,
Deepak Kumar