sysinfo dns server 14 nadia

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untnu
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sysinfo dns server 14 nadia

Postby untnu » Tue Mar 05, 2013 5:54 pm

i see 127.0.1.1 listed in dns...never encountered that before.

uhm? i just use ff for inet usage.

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karlchen
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Re: sysinfo dns server 14 nadia

Postby karlchen » Tue Mar 05, 2013 6:22 pm

Hello, untnu.

Ubuntu 12.10 / Mint 14 uses a daemon named dnsmsaq in order to cache frequently queried addresses. This is done in order to reduce the number of real DNS queries. dnsmasq listens on 127.0.0.1 tcp port 53.
If the answer to a DNS query is not found in the dsnmasq cache dnsmasq will pass the DNS query to the DNS server which your machine should query.
For a lot of home machines this will be the DSL router box.

So how can you find out which external DNS server is your primary DNS server?

Open a terminal window and execute the command

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ps  axu | grep dnsmasq
On my system this will return this output

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nobody    1009  0.0  0.0   6888  1228 ?        S    21:38   0:00 /usr/sbin/dnsmasq --no-resolv --keep-in-foreground --no-hosts --bind-interfaces --pid-file=/var/run/sendsigs.omit.d/network-manager.dnsmasq.pid --listen-address=127.0.0.1 --conf-file=/var/run/nm-dns-dnsmasq.conf --cache-size=0 --proxy-dnssec

You can find out what each commandline argument means by going through the dnsmasq manpages.

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man dnsmasq

Let us inspect just this part here for the moment:

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--conf-file=/var/run/nm-dns-dnsmasq.conf
dnsmasq uses the configuration file /var/run/nm-dns-dnsmasq.conf.
The name nm-dns-dnsmasq.conf indicates that it is generated (dynamically) by Networker Manager.
On my machine there is not much in this file, just one line:

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cat /var/run/nm-dns-dnsmasq.conf
server=192.168.178.1
This is the internal address of my DSL router. So dnsmasq will pass on any DNS query for which there is no matching entry in its cache to my router.
The router in turn will pass the query on to the DNS servers of my internet provider. In order to verify the router does do so we would have to inspect the router. But doing so is beyond the scope of your question.

So whenever you navigate to an internet address in your Firefox, Firefox has to resolve the internet address into an IP address. Therefore Firefox will ask dnsmasq to resolve the address.
If dnsmasq already knows the answer, it will return it to Firefox.
If dnsmasq does not yet know the answer, it will ask the external DNS server. It will return the answer of the external DNS server to Firefox and remember it ini its cache in case Firefox should ask for the same address later on.
Firefox will try to connect to the received IP address.

HTH,
Karl
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Old bugs good, new bugs bad! Updates are evil: might fix old bugs and introduce no new ones.


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