ASA DHCP MAC funny buggers

In a simple deployment I needed to add a DHCP server to the ASA. No worries there. Quick little configuration like this does the job.

dhcpd address 192.168.36.10-192.168.36.50 dmz36
dhcpd lease 3600 interface dmz36
dhcpd dns 192.168.36.1
dhcpd domain ciscoinferno.net
dhcpd enable dmz36

The above configuration simply defines a range, lease time, DNS server, domain, and finally initiates the server. It was when I was confirming a lease did I notice something odd.

ciscoasa# sh dhcpd binding
IP address    Client Identifier  Lease expiration     Type
192.168.36.26  0108.0027.4152.9e  3291 seconds        Automatic

See it? A 14 character MAC address. What on earth? Well we know that MAC addresses use a 12 character address. I quickly confirmed the lease on my TinyCore client.

ifconfig eth1
eth1 Link encap:Ethernet HWaddr 08:00:27:41:52:9E
 inet addr:192.168.36.26 Bcast:192.168.1.255 Mask:255.255.255.0
 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1

We can see here that our MAC addresses match. So what is this extra two characters in the MAC address field? I wasn’t sure what to search and looked through the 8.4 configuration guide and it yielded nothing.  Bobmccouch lended some advice to this.

11:14 < pandom_> Trying to find cisco's reasoning in making the client ID on ASA dhcp pool 14
 digitas rather than 12
11:15 < pandom_> ie 08:00:27:41:52:9E becomes 0108.0027.4152.9e
11:15 < bobmccouch> pandom_: the 01 is the media type
11:15 < bobmccouch> 01=ethernet

So there you go. 01 indicates the media type is ethernet. The more you know, hey?

 

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