cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
546
Views
0
Helpful
3
Replies

DHCP trouble

adelium904
Level 1
Level 1

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>

3 Replies 3

Philip D'Ath
VIP Alumni
VIP Alumni

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.

Thanks for the answer.

Why does the devices get another IP address?

Rolf Fischer
Level 9
Level 9

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

Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: