guarantee RFC standardized hostname

[Glenn Satchell]

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
>
>