DHCP trouble

[adelium904]

Hi I have a strange situation with my DHCP pool.

As you can see below, I made some reservation for the first 3 devices.

The thing I do not understand is that the devices get another IP address? Moreover, their Mac address is transfomed:

From 008e.7135.b000 to 0100.7135.4db0.00

From 008e.7135.b440 to 0100.7135.4db4.40

From b835.4789.8465 to 01b8.3547.8984.65

Why? Where does it come from?

Thanks!

<code>sh ip dhcp binding
Bindings from all pools not associated with VRF:
IP address          Client-ID/             Lease expiration        Type
            Hardware address/
            User name
192.168.100.1       0071.354d.b000          Infinite                Manual
192.168.100.2       0071.354d.b440          Infinite                Manual
192.168.100.3       b835.4789.8465          Infinite                Manual
192.168.100.6       0100.7135.4db0.00       Jun 26 2017 02:08 PM    Automatic
192.168.100.7       0100.7135.4db4.40       Jun 26 2017 02:59 PM    Automatic
192.168.100.8       01b8.3547.8984.65       Jun 26 2017 04:55 PM    Automatic

sh mac
Destination Address    Address Type    VLAN    Destination Port
-------------------    ------------    ----    -----------------
7648.7a42.ffc6        Self                1    Vlan1
0071.354d.b000        Dynamic             1    GigabitEthernet0
b835.4789.8465        Dynamic             1    GigabitEthernet0
0071.354d.b440        Dynamic             1    GigabitEthernet0
</code>

[Philip D'Ath]

008e.7135.b000 sounds like a MAC address.  0100.7135.4db0.00 sounds like a DHCP client identifier.

You can match on either in your DHCP pool.

[adelium904]

Thanks for the answer.

Why does the devices get another IP address?

[Rolf Fischer]

Hi,

this document may answer your questions:

Understanding and Troubleshooting DHCP in Catalyst Switch or Enterprise Networks

Setting Manual Bindings

There are two ways to set up manual bindings; one is for the Windows host, and the other is for non-Windows hosts. There are two different commands used to configure; one is for Microsoft DHCP clients, and the other is for non-Microsoft DHCP clients: DHCP client-identifier  (manual binding - Microsoft DHCP clients) and DHCP hardware-address  (manual binding - non-Microsoft DHCP clients). The reason for two different commands is that a PC that runs with Windows modifies its MACs, and a 01 is added at the beginning of the address. These are the sample configurations:

•The following is the configuration for Microsoft DHCP clients

configuration terminal
ip dhcp pool new_pool
host ip_address subnet_mask
client-identifier 01XXXXXXXXXXXX
 !--- xxxxxx represents 48 bit MAC address prepended with 01

•The following is the configuration for non-Microsoft DHCP clients

configuration terminal
ip dhcp pool new_pool
host ip_address subnet_mask
hardware-address XXXXXXXXXXXX
 !--- xxxxxx represents 48 bit MAC address

I think the distinction between MS and non-MS clients in the document is a bit oversimplified; the actual question is whether or not the clients use DHCP option 61 (see RFC 2131 4.2 and RFC 2132 9.14). If so, you need to prepend a '01' as shown in the first configuration example.

HTH
Rolf