How does DHCPD determine what IP address to assign and...

[Ryan McCain]

>>> On Fri, Jan 4, 2008 at  8:34 AM, in message
<200801041434.m04EYkZ6026585 at mail.uniq.com.au>, Glenn Satchell
<Glenn.Satchell at uniq.com.au> wrote: 

>>Date: Thu, 03 Jan 2008 12:29:22 -0600
>>From: "Ryan McCain" <Ryan.McCain at dss.state.la.us>
>>To: <dhcp-users at isc.org>
>>Subject: Re: RE: How does DHCPD determine what IP address to assign and...
>>
>>>>> On Thu, Jan 3, 2008 at  6:24 AM, in message
>><200801031224.m03COxkP021770 at mail.uniq.com.au>, Glenn Satchell
>><Glenn.Satchell at uniq.com.au> wrote: 
>>
>>>>Date: Wed, 02 Jan 2008 14:01:03 -0600
>>>>From: "Ryan McCain" <Ryan.McCain at dss.state.la.us>
>>>>To: <dhcp-users at isc.org>
>>>>Subject: Re: RE: How does DHCPD determine what IP address to assign and...
>>>>
>>>>
>>>>class "DialUp" {
>>>>    match if (substring(suffix(dhcp-client-identifier,7),0,5)="Async")
>>>>
>>>>                   or
>>>>                 
>>>>(substring(suffix(dhcp-client-identifier,6),0,5)="Async") ; 
>>>>            log (info, " Matched Dialup Rule");
>>>>                        }
>>>>}
>>> 
>>> ok Ryan, let's break it down. I assume you have looked at the dhcp-eval
>>> man page to get the descriptions for substring() and suffix().
>>> 
>>> Let's look at the first evaluation and start with the assumption that
>>> option dhcp-client-identifier is the string
>>> ABCDFEGHIJKLMNOPQRSTUVWXYZ.
>>> 
>>> suffix(option dhcp-client-identifier, 7) is the last 7 chars from out
>>> string, in this case TUVWXYZ.
>>> 
>>> substring("TUVWXYZ", 0, 5) is the string starting at position 0 and is
>>> 5 chars long, in this case TUVWX.
>>> 
>>> Now we are determining membership of the class if this final substring
>>> is equal to "Async".
>>> 
>>> The second line uses a suffix of length 6. So it would evaluate the
>>> suffix bit to be the last 6 chars, UVWXYZ. Doing a substring of that
>>> gives UVWXY.
>>> 
>>> Now in your case to match the option dhcp-client-ientifier must be
>>> something like
>>> 
>>> XXXXXXAsyncXX or XXXXXXXXXXAsyncX
>>> 
>>> to log this, in the global section, ie outside the class and subnet put
>>> something like
>>> 
>>> log(concat("dhcp-client-identifier is ", option
>>> dhcp-client-identifier));
>>> 
>>> Looking at packet captures, global log entries, etc, does the string
>>> look like that pattern? Often using a tool like wireshark will give
>>> better results because there may be unprintable binary chars in the
>>> string, especially sometimes a trailing null byte which you can't see
>>> but gets counted in the suffix...
>>> 
>>> regards,
>>> -glenn
>>
>>I haven't had a chance to look at the network today.  Hopefully tomorrow I'll 
> 
> have time to get wireshark up.  
>>
>>From what you typed it doesn't look like the syntax I'm using will
>>always work. The string 'Async' could be anywhere in the UID.
>>
>>Is there an equivalent of "*Async*' using DHCP pattern matching?  
> 
> Regular expressions looks like it is in 4.0.0:
> 
>   match if option dhcp-client-identifier ~= "Async";
> 
> might do the trick. Is it feasible for you to upgrade to 4.0.0?
> 
>>Perhaps using the 'exists' condition?  
> 
> exists(dhcp-client-identifier) only returns true or false based on
> whether that option was sent by the client.
> 
> Can the dial in servers be configured to pass the client identifier in
> a more consistent way?
> 
> regards,
> -glenn

Glenn,

Thanks again for your support.  As it stands right now I am not able to upgrade to DHCP 4.x.  That would void the support we get from Novell.  However, if it comes down to us not having support or DHCP not working, I might be able to convince the higher ups to allow us to upgrade to v4.x just on our 2 DHCP servers.

Also, there is no way the dial in servers can be configured to pass the client identifier in another format according to our Cisco guy.  He says its internal Cisco stuff he doesn't have access to.

As far as you know, unless we upgrade to v4.x, there is no way we can accomplish this?

Thanks,
Ryan