[Dnsmasq-discuss] Fake reverse lookups from cache

Simon Kelley simon at thekelleys.org.uk
Sat Jan 31 22:21:45 GMT 2015


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On 31/01/15 13:57, Joachim Zobel wrote:
> Hi.
> 
> I am currently thinking about implementing a feature in dnsmasq
> that I consider highly useful. When I do a netstat-nat on my router
> (asuswrt), I will mostly get reverse names that are about as useful
> as ip adresses. So my idea is to implement a configuration option
> for dnsmasq:
> 
> --fake-reverse Fake reverse lookups by using the cache. Reverse
> lookups are satisfied by using the cached forward entries if
> possible. Note that this does not give the same result as the
> reverse lookup. It will give a better results in most situations,
> since it will return a name that has actually been before.
> 
> So I have two questions:
> 
> 1. What are the cons?

Good question. Here's a couple I can think of.

1) If the forward entry has expired from the cache, or is otherwise
lost (dnsmasq restart) then you can't do this and will have to get the
"real" answer. That's introduced some indeterminacy as a start.

2) Whilst useful for you to look at the output of netstat-nat, you're
also affecting everything else that uses reverse lookups. I'm not sure
if there would be consequences to that, but can we be sure there won't.

> 2. What are my chances to have such a patch accepted in dnsmasq
> trunk?

Another good question. I'm kind-of ambivalent about this. It seems
like Yet Another Config Option, it's of some, but niche, use. 99% of
all dnsmasq users won't use it (but that's true of quite a few dnsmasq
features.) I'm not sure, but I'd be interested in other's opinions too.

Cheers,

Simon.

> 
> Sincerely, Joachim
> 
> 
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