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Client MAC Addresses with 01 Prefix on DHCP

jcribb
Level 1
Level 1

Hello,

We are observing some weird output on our DHCP bindings.  For some reason when I view DHCP bindings on our main switch it prepends each MAC address of the client with a 01 in front of it.  However if I view the MAC address table it uses the standard 48bit output and display.  Any reason for this?  It is more of an annoyance than anything but it can make tracing clients on the network more time consuming.  Here is a sample output from our switch DHCP bindings:

10.20.5.117    01d4.bed9.411d.df       Jun 04 2013 08:27 AM    Automatic

10.20.5.118    01e0.db55.df73.70       May 31 2013 08:25 AM    Automatic

10.20.5.121    01b8.ca3a.d2de.bb       Jun 04 2013 09:02 AM    Automatic

10.20.5.123    01b8.ca3a.d1ea.cf       Jun 04 2013 08:04 AM    Automatic

10.20.5.124    01d4.bed9.3218.dc       Jun 04 2013 09:15 AM    Automatic

10.20.5.126    01a8.2066.54d6.d6       Jun 04 2013 09:55 AM    Automatic

10.20.5.128    3cd9.2b7b.bdc0          Jun 03 2013 09:04 PM    Automatic

10.20.5.133    001c.4244.5fbc          Jun 04 2013 10:05 AM    Automatic

10.20.5.137    01e0.db55.e12a.37       Jun 04 2013 07:48 AM    Automatic

10.20.5.143    01e0.db55.e927.c2       Jun 04 2013 09:29 AM    Automatic

Another weird item to note is that we do have some entries in the binding list that show the standard format MAC address as you can see from the list above.

NOTE: We are doing DHCP on the switch and we have a Cisco powered wireless network.

- James

1 Reply 1

cadet alain
VIP Alumni
VIP Alumni

Hi,

the MAC addresses prepended with 01 are the client-identifiers used by the hosts like Windows hosts and the one without the 01 prepended are from linux hosts or printers for example.So this is a normal behaviour you are observing.

this is explained here:http://tools.ietf.org/html/rfc2131

Regards

Alain

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