Re: [dhcwg] Question: in RFC3046 why did Agent Subnet Mask Sub-optiondie

David W. Hankins wrote:
> On Fri, Mar 09, 2007 at 11:50:28AM +0000, Simon Kelley wrote:
> 
>>>I don't like the vector to this line of reasoning.
>>
>>Would you care to explain why?
> 
> 
> Sure.
> 
> 
>>You should look at dnsmasq, which makes it work fine.
> 
> 
> I know dnsmasq works, I meant for the relay case.
> 
> Adopting a change like this would create a 'subset of compatibility'
> where dnsmasq is compatible with certain relays (and network designs
> it turns out) but not others.
> 
> It "doesn't work" for any device that adds relay agent options and
> either doesn't know about any prefixes on that network (such as a
> switch), or doesn't know about /all/ of the prefixes on that network
> (such as one of multiple routers, or one of multiple hosts on that
> network).
> 
> If it were just a 'dnsmasq works with relay A but not B' thing, I
> might be convinced if there were a really good reason (but I think
> 'not configuring the network mask' isn't good enough).  But 'network
> architecture A but not B' is pushing it even further for me.

This is already the situation for dnsmasq: currently "shared networks" 
work with directly connected networks but for networks behind relays, 
shared networks are not allowed. So providing this facility doesn't add 
another exception, it allows networks behind relays to work in the same 
way as directly connected networks and removes the anomally. For relays 
which don't support the new option, nothing changes.

> 
> DHCP tries hard not to care how the network is put together.  It is
> a bad vector to create DHCP protocol work that dictates a network
> design,

I don't think it does.
> and intentionally introduces relay<->server compatibility
> problems.
>

I have some sympathy with this, but, at least for dnsmasq, it's possible 
to argue that it reduces compatibility problems.

Cheers,

Simon.

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