guarantee RFC standardized hostname

[Kevin Fitzgerald]

I tried Glenn's suggestion, and while it did parse correctly, it does not
seem to have had the desired results.  I watched the logs and soon enough
"android_xxxxyyyyyzzzzzz123" rolled thru.

I was worried that it seemed too good to be true.  I am not convinced that
it isn't a small syntax error that I have to work out, so I will play around
with this some more.


On Thu, Aug 25, 2011 at 9:35 AM, Glenn Satchell
<glenn.satchell at uniq.com.au>wrote:

> man dhcp-eval
> ...
>     data-expression-1 ~= data-expression-2 data-expression-1  ~~
>     data-expression-2
>
>       The ~= and ~~ operators (not  available  on  all  systems)
>       perform  extended  regex(7)  matching of the values of two
>       data  expressions,  returning  true  if  data-expression-1
>       matches  against the regular expression evaluated by data-
>       expression-2, or false if it does not match or  encounters
>       some  error.   If  either the left-hand side or the right-
>       hand side are null, the result  is  also  false.   The  ~~
>       operator  differs from the ~= operator in that it is case-
>       insensitive.
>
> So you might want something like this then, where you list all the "good"
> characters in the regex string on the right? I haven't tested this, but I'm
> sure you get the idea...
>
> if exists host-name and option host-name ~~ "[a-z0-9.-]+" {
>
>        ddns-hostname = concat (lcase (option host-name) , "-" ,
> binary-to-ascii(10 , 8 , "-" , leased-address));
> }
> else {
>        ddns-hostname = concat("dhcp-" , binary-to-ascii(10 , 8 , "-"
> leased-address));
> }
>
> regards,
> -glenn
>
>
> On 08/25/11 07:25, Kevin Fitzgerald wrote:
>
>> Hi Group,
>>
>> For quite some time we have been generating DHCP ddns hostnames as
>> follows:
>>
>> if exists host-name {
>>         ddns-hostname = concat (lcase (option host-name) , "-" ,
>> binary-to-ascii(10 , 8 , "-" , leased-address));
>>         }
>>     else {
>>         ddns-hostname = concat("dhcp-" , binary-to-ascii(10 , 8 , "-" ,
>> leased-address));
>>         }
>>
>> This is not an uncommon format.  It helps us ensure unique host names on
>> our network.  Lately I notice a handful of user devices that present
>> host names with invalid characters, such as android_blah or "nintendo
>> 3ds" with a space in the middle (no quotes).
>> What are you folks doing to mitigate this?  As it stands these users do
>> not receive valid NS records and we get a bevy of log messages when
>> illegal characters are in the hostname.
>>
>> - I have seen mention of the use of regex in the man pages for
>> dhcp-eval.  Is there a method to examine the host-name for invalid
>> characters, replacing them with a hyphen or otherwise?    (Is there
>> REGEX evaluation available within dhcpd.conf)
>> - if there is no way to do a character by character replace, can I fail
>> down to my else condition, simply prepending dhcp- to the front of the
>> IP address?
>> --
>> K. Fitzgerald
>> UALR Information Technology Services
>>
>>
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>



-- 
Kevin Fitzgerald
UALR Information Technology Services
501-916-5019
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