[Dnsmasq-discuss] IP address based on switch port number (option 82)

[richardvoigt at gmail.com]

On Wed, Feb 17, 2010 at 5:03 AM, Simon Kelley <simon at thekelleys.org.uk> wrote:
> Ignacio.Bravo at belden.com wrote:
>> Simon Kelley <simon at thekelleys.org.uk> wrote on 16/02/2010 14:27:36:
>>
>>> fakeroot debian/rules binary
>> I found a problem when fakerooting (sorry for my ignorance) Do I need to
>> install additional tools containing this lib?:
>> Package libidn was not found in the pkg-config search path.
>> Perhaps you should add the directory containing `libidn.pc'
>> to the PKG_CONFIG_PATH environment variable
>> No package 'libidn' found
>
> That's a mismatch between what's needed to compile Ubuntu's current
> dnsmasq package and the latest one. the fix is
>
> sudo apt-get install libidn11-dev
>
>
>>> The magic you need is that you can invert tags, so make the last line
>>>
>>>
>> dhcp-range=net:#switch1,net:#puerto3,10.10.35.40,10.10.35.42,255.255.255.0
>>> Then it can only be used when none of the port specific tags are in use.
>>
>> The problem I see here is switch1 tag is common to all switch1-ports. So I
>> discard all switch1 ports when I write: net:#switch1
>>
>> I feel I need something like: #(switch1ANDport3) instead
>> #(switch1)AND#(port3)
>>
>> Is it possible to set something like #(net:switch1,net:port3)? or maybe an
>> OR function so that different conditions (switchANDport) apply to the same
>> range?
>

Can't the option-matching lines which set e.g. port1 also set e.g.
nopool, then use #nopool in the dhcp-range line?

I guess there might need to be nosw1pool, nosw2pool, nosw3pool, and
then dhcp-range such as net:switch1,net:#nosw1pool

Or maybe even just

net:switch1,net:#port3,net:#port4 (pool which is valid for all switch1
ports except 3 and 4)

> Good point. Your requirements exceed what it's currently possible to
> express using the tag system.
>
> Maybe there needs to be something to calculate and arbitrary boolean
> expression on tags
>
> declare-tag set:newtag, !(switch1 & port1)
>
> Joy, the options code finally becomes a full recusive-descent parser.

Actually, I think you can avoid that without loss of generality.

By DeMorgan's theorem, the AND and NOT operations currently available
are sufficient to define any expression.  You just need a way to do
grouping, which a syntax for setting one tag conditionally based on
another tag would do.

Remember that the example given doesn't need a complement applied, you
can negate it in the match later.

Since "if" is a very well understood concept, I'd propose

tag-if switch1,port1 newtag

Where newtag gets set if all listed tags are matched.  Using multiple
tag-if lines lets you effectively OR things together (this yields
sum-of-products capability).  Allow a user to unset a tag with

tag-if #switch1,port15 #newtag

for even more flexibility, but now all tag-if commands need to be
processed in order.

>
>
> Let me think about this a bit more.
>
>
> Simon.
>
>>
>> Thanks
>> Ignacio
>>
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>>
>>
>
>
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