Cisco IOS DHCP Client Identifier

Hello, everyone!

I’ve a few questions about the client ID.

Most host devices that use DHCP client will use their MAC address as the client ID. Cisco IOS however uses one of their own formats, this can be a problem if you need to get an IP address from the DHCP server based on your MAC address. For example, some cable providers check the MAC address of a client before handing out an IP address.

If I had a router connected to the ISP and I issued the ip address dhcp command on that interface, there is a possibility that it wouldn’t receive an IP address just because its… using a different format?

My another question is, I’ve enabled a host for DHCP and this is the client ID it included in the DHCP message.

However, in the output of show ip dhcp binding command, the client ID is just not the same there

And my last question is, why Client ID? Why not just use the MAC address all the time? What’s the reason behind Cisco using their own format?

Thank you all!