need help understanding class matching
Simon Hobson
dhcp1 at thehobsons.co.uk
Tue Aug 30 16:09:57 UTC 2011
jeffrey j donovan wrote:
> > Really ?
>> The hardware field (for an ethernet network) will contain a 1
>>(0x01) followed by the 6 bytes of MAC address - it does not contain
>>an ascii representation of those bytes. To fetch the OUI of the MAC
>>address you do need to get bytes 1 to 3 of the hardware and compare
>>with a 3 byte string.
>
>okay not really, the syntax works but the clients are not matching.
That's what I thought
>i did see where someone did a conversion prior to the substring
>line. but I did not understand it;
>binary-to-ascii (16, 8, "", substring (hardware, 6, 1))),2) );
>
>
>im thinking this might work
>
>ahhh,..
>i found this
>http://blather.michaelwlucas.com/archives/962
>
>class "sip-phone" {
>match if (binary-to-ascii (16,8,":",substring(hardware, 0, 4)) = "1:0:3:e3")
>or (binary-to-ascii (16,8,":",substring(hardware, 0, 4)) = "1:0:3:6b")
>or (binary-to-ascii (16,8,":",substring(hardware, 0, 4)) = "1:0:7:eb");
>log (info, (binary-to-ascii (16,8,":",substring(hardware, 0, 4))));
>}
>
>makes sense when I see it.
You do **NOT** have to do this. You can if you wish, but it is not necessary.
binary-to-ascii does what it says, and with the options specified
will convert the binary hardware address to a string representation.
Then you can match against a string.
However, you can save some typing, and processing time*, by just
specifying the match strings as the binary string you want to match
against.
* When a packet comes in, you have to do the binary to ascii
conversion, for each packet and for each time it's used in a class
match.
so you can do :
binary-to-ascii (16,8,":",substring(hardware, 1, 3)) = "0:11:ba3"
or you can so :
substring(hardware, 1, 3) = "\x00\x11\xba"
and I think (someone correct me if I'm wrong) you can write that
latter one as (note the lack of quotes) :
substring(hardware, 1, 3) = 00:11:ba
--
Simon Hobson
Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.
More information about the dhcp-users
mailing list