[Dnsmasq-discuss] Very accurate bandwidth tracking...
Simon Kelley
simon at thekelleys.org.uk
Tue May 10 12:10:43 BST 2011
Jan Seiffert wrote:
> 2011/5/10 Ed W <lists at wildgooses.com>:
>> Slightly related - I see that --all-servers might have become the default now?
>> http://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2010q2/003942.html
>>
>> Is there some way to disable this and use "known to be up"? The reason is that
>> I'm seeing a large ICMP "unreachable" response generated for the slower response,
>> plus the additional bandwith, eg tcpdump for a request for www.yahoo.co.uk:
>>
> [snip - tcpdump chatter]
>
> If 8.8.8.8 and 8.8.4.4 are your upstream servers, then what you see is
> not all-servers. It's dnsmasqs devious plan to take world domination
> No.. ;)
> Every few query dnsmasq asks all upstream server to measure which is
> faster/more reliable.
> This is not unimportant, also to minimize traffic (banging on an
> unresponsive server is wasting traffic).
> You can see it from the dump. For the first query (AAAA) dnsmasq asks
> both, 8.8.4.4 answers first, the second query for A is only send to
> 8.8.4.4.
>
> You probably want to play with your firewall to suppress those port
> unreachable, at least in this special case the upstream DNS server
> gives a **** about your port status.
>
> [snip]
>> Note, if there is no explicit option for this then I think "strict-order" is actually satisfactory as a workaround!
>>
>
> But in case of upstream failure "strict-order" can screw things up, as
> far as i remember, because then dnsmasq will stick to the strict order
> and keep sending traffic to an unresponsive upstream.
Jan's answer is completely correct. The only thing to add is that the
changes in 2.53 don't make --all-servers the default, they change the
behaviour when there is more than one server for a particular domain:
--server=/example.net/1.2.3.4
--server=/example.net/2.3.4.5
to do the equivalent of --all-servers _for_queries_to_that_domain.
The behaviour for general (not domain-specific) upstream servers is
unchanged.
Cheers,
Simon.
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