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 dmz36
dhcpd lease 3600 interface dmz36
dhcpd dns
dhcpd domain
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  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: Bcast: Mask:

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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