Option 43 for Cisco LWAP

[Glenn Satchell]

Hi Brendan

There are two ways to encode vendor specific options. The first way
encodes a single value. The way you specified with an option space
allows you to encode multiple values in the string.

The values prepended are the option number, the length, and the bytes
that make up the value.

2b 06 f1 04 ac 11 fe 29

2b = 43 written in hex
06 is the length
04 ac 11 fe 29 are the 6 data bytes

2b 08 2b 06 f1 04 ac 11 fe 29

2b = 43 encoded in hex, the dhcp option number
08 is the total length of the dhcp option
2b = 43 in hex, the sub option number
06 the length of the sub option
f1 04 ac 11 fe 29 are the six data bytes

See the dhcp-options man page and search for
"option vendor-encapsulated-options" and
"VENDOR ENCAPSULATED OPTIONS".

regards,
-glenn

>Date: Mon, 20 Oct 2008 13:22:41 -0600
>From: "Brendan Forsyth" <bff at pvhs.org>
>To: <dhcp-users at isc.org>
>Subject: RE: Option 43 for Cisco LWAP
>
>That did it.  Thank  you Robert!
> 
>Brendan
>
>>>> "Colantuoni, Robert" <rgc at buffalo.edu> 10/20/2008 1:06 PM >>>
> 
>This is what I have in my config:
> 
>        option controllers code 43  = string;
> 
>        # 
http://www.cisco.com/univercd/cc/td/doc/product/wireless/airo1130/1130hig5/113h_
g.htm#wp1007971 
>        #
>        # The hex string is assembled by concatenating the TLV values shown 
below:
>        # Type + Length + Value
>        #
>        # Type is always f1(hex). Length is the number of controller management 
IP addresses
>        #  times 4 in hex. Value is the IP address of the controller listed 
sequentially in hex.
>        #
>        # For example, suppose that there are two controllers with management 
interface IP addresses,
>        #  10.126.126.2 and 10.127.127.2. The type is f1(hex). The length is 2 
* 4 = 8 = 08 (hex).
>        #  The IP addresses translate to 0a7e7e02 and 0a7f7f02. Assembling the 
string then yields
>        #  f1080a7e7e020a7f7f02. The resulting Cisco IOS command added to the 
DHCP scope is listed below:
>        #
>        # option 43 hex f1080a7e7e020a7f7f02
>
> 
>         # 10.3.240.2 == 0A.03.F0.02
>         # 10.3.240.4 == 0A.03.F0.04
>         option controllers f1:08:0a:03:f0:02:0a:03:f0:04;
> 
> 
> 
>
>----------------------------------
>
>Robert G Colantuoni
>CIT - Operational Support Services
>University at Buffalo
>rgc at buffalo.edu 
>716.645.3552
>
> 
>
>
>
>From: dhcp-users-bounce at isc.org [mailto:dhcp-users-bounce at isc.org] On Behalf Of 
Brendan Forsyth
>Sent: Monday, October 20, 2008 2:57 PM
>To: dhcp-users at isc.org 
>Subject: Option 43 for Cisco LWAP
>
>Here is my problem.  When I use the Cisco DHCP server and add option 43 for 
telling the access points about where the WiSM controller is, everything works 
fine.  However from DHCP ISC v3.0.5, it doesn't.  Here are the two configs:
> 
>Cisco:
>ip dhcp pool auto-pool
>   network 172.17.112.0 255.255.255.0
>   domain-name pvh.org
>   option 43 hex f104.ac11.fe29
>   option 60 ascii "Cisco AP c1200"
>   default-router 172.17.112.1 
>A wire shark dump of the ACK shows this:
>Option: (t=43, l=6) Vendor-Specific Information
>   Option:  (43) Vendor-Specific Information
>   Length:  6
>   Value: F104AC11FE29
> 
>The packet dump shows 2b 06 f1 04 ac 11 fe 29
> 
>ISC DHCP
> 
>option space Cisco_LWAPP_AP;
>option Cisco_LWAPP_AP.server-address code 43 = string;
>        class "Cisco AP c1200" {
>                match if option vendor-class-identifier = "Cisco AP c1200";
>                option dhcp-parameter-request-list 43;
>                option vendor-class-identifier "Cisco AP c1200";
>                vendor-option-space Cisco_LWAPP_AP;
>                option Cisco_LWAPP_AP.server-address f1:04:ac:11:fe:29;
>        }
>Option: (t=43, l=8) Vendor-Specific Information
>   Option:  (43) Vendor-Specific Information
>   Length:  8
>   Value: F104AC11FE29
> 
>The packet dump shows 2b 08 2b 06 f1 04 ac 11 fe 29
> 
>Note the two extra octets in the DHCP dump.  Also the class definition was 
obtained from Cisco's site about configuring ISC DHCP for option 43 
functionality.
> 
>Any advice is appreciated.
> 
>Thanks,
> 
> 
> 
>Brendan Forsyth
>Senior System Administrator
>Poudre Valley Health Care
>3702 Automation Way
>Fort Collins CO 80525
>bff at pvhs.org 
>(970) 495-7731 office
>
>
>
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