The string under the DHCP client-id/hardware address represents the ASCII equivalent of the client identifier. See the output of 'show ip DHCP bindings' on a router operating as a DHCP server:
IP address | Client-ID/ Hardware address | Lease expiration | Type |
| | | |
192.168.1.3 | 0063.6973.636f.2d30.3030.612e.6238.3939.2e31.3163.352d.566c.3130.31 | Mar 16 1993 10:09 PM | Automatic |
192.168.1.4 | 0063.6973.636f.2d30.3030.662e.3233.3339.2e36.3963.332d.566c.3130.31 | Mar 16 1993 10:10 PM | Automatic |
This string represents the ASCII equivalent of the client identifier. For example, if we convert the client ID (0063.6973.636f.2d30.3030.612e.6238.3939.2e31.3163.352d.566c.3130.31) by using the ASCII table, we will get cisco-000a.b899.11c5-Vl101. The format Cisco uses is cisco-<mac-address>-<interface>.
This is the ASCII value (in Hex) of the character. We can find a few ASCII codes below but we need to search for a full set.
Hex Decimal Character (symbol)
-----------------------------------------------------------------
0x30 48 0
0x31 49 1
0x32 50 2
....
0x39 57 9
0x61 97 a
0x62 98 b
0x63 99 c
.....
0x7a 122 z
-------------------------------------------------------------------------------------------------------------
For example, the string 'cisco' will be represented in ASCII (hex) as 63 69 73 63 6f
----------------------------------------------------------------------------------------c i s c o
So here in this example we assigned DHCP address to our vlan101 interface.
By default, DHCP implementations typically employ the client's MAC address for this purpose, but the DHCP protocol allows other options as well. In any case, in order for DHCP to function, we must be certain that no other client is using the client ID we choose, and we must be sure the DHCP server will accept it. What is termed the Client ID for the purposes of the DHCP protocol is whatever is used by the protocol to identify the client computer.
A client identifier (DHCP option 61) can be a hexadecimal or an ASCII value. By default, the client identifier is an ASCII value. That is what happens if we just use ip address dhcp without any options. We can override the default by using ip address dhcp client-id <interface> command, and then it will use the hexadecimal MAC address of the named interface as the client identifier.
There is also DHCP option 12 that is used to send the hostname to the Server. By default option 12 also will be sent with the configured hostname as the value, but we can change it with ip address dhcp hostname host-name.
