04-13-2010 06:21 AM - edited 03-06-2019 10:35 AM
Using ' show ip DHCP bindings ' on a router operating as a DHCP server I have strange entries under the DHCP client-id/hardware address ( example below ) , should they correlate to the clients MAC address ?
IP address Client-ID/ Lease expiration Type
Hardware address
192.168.1.3 0063.6973.636f.2d30. Mar 16 1993 10:09 PM Automatic
3030.612e.6238.3939.
2e31.3163.352d.566c.
3130.31
192.168.1.4 0063.6973.636f.2d30. Mar 16 1993 10:10 PM Automatic
3030.662e.3233.3339.
2e36.3963.332d.566c.
3130.31
Solved! Go to Solution.
04-13-2010 04:39 PM
That string represents the ASCII equivalent of the client identifier. For eg. if you convert the client ID(0063.6973.636f.2d30.3030.612e.6238.3939.2e31.3163.352d.566c.3130.31) by using the ASCII table, you will get cisco-000a.b899.11c5-Vl101. The format cisco uses is cisco-
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, you must be certain that no other client is using the client ID you choose, and you 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 you just use ip address dhcp without any options. You can override the default by using ip address dhcp client-id <interface> command, 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 you can change it with ip address dhcp hostname host-name.
Shahal, CCIE
04-13-2010 04:39 PM
That string represents the ASCII equivalent of the client identifier. For eg. if you convert the client ID(0063.6973.636f.2d30.3030.612e.6238.3939.2e31.3163.352d.566c.3130.31) by using the ASCII table, you will get cisco-000a.b899.11c5-Vl101. The format cisco uses is cisco-
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, you must be certain that no other client is using the client ID you choose, and you 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 you just use ip address dhcp without any options. You can override the default by using ip address dhcp client-id <interface> command, 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 you can change it with ip address dhcp hostname host-name.
Shahal, CCIE
04-14-2010 12:24 AM
Hi Shalal,
That's great ! - thanks for the reply
Can you walk me through how you converted (0063.6973.636f.2d30.3030.612e.6238.3939.2e31.3163.352d.566c.3130.31) to cisco-000a.b899.11c5-Vl101
I can't quite see how the conversion works , I'm OK with dec to HEX etc ... but can't match the string ?
Thanks again for your help
04-14-2010 07:39 PM
Hi,
What I mean is the ASCII value(in Hex) of the character. You can find a few ASCII codes below but you can 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 eg. the string 'cisco' will be represented in ASCII (hex) as 63 69 73 63 6f
----------------------------------------------------------------------------------------c i s c o
-------------------------------------------------------------------------------------------------------------
Does that make sense now?.
Regards,
Shahal.
04-15-2010 12:11 AM
That's great, thanks again
Discover and save your favorite ideas. Come back to expert answers, step-by-step guides, recent topics, and more.
New here? Get started with these tips. How to use Community New member guide