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From André Warnier (tomcat) ...@ice-sa.com>
Subject Re: help for DNS queries
Date Tue, 06 Aug 2019 12:13:44 GMT
On 06.08.2019 03:32, Paulina wrote:
>
>
>
>>
>>
>> On Mon, Aug 5, 2019, at 06:50, Paulina wrote:
>>>
>>> I have been using a cloud host, it seems I have a unnormal DNS resolver
>>> entry:
>>
>> And what exactly is unnormal in:
>>
>>> nameserver 127.0.0.53
>>> options edns0
>>
>> ???
>
> Sorry my mistake.
> After checking the documents I just know what's the difference between Caching server
and
> auth-server for DNS queries.
> So it seems I am using a caching server whose IP addr is 127.0.0.53.

Does this article provide any help for you ?
https://askubuntu.com/questions/1012641/dns-set-to-systemds-127-0-0-53-how-to-change-permanently

I got this by asking Google for "what is 127.0.0.53"

Similarly, asking for "what is LLMNR" gets you this :
https://en.wikipedia.org/wiki/Link-Local_Multicast_Name_Resolution

and I also find plenty of information that suggests that you should disable it..
(but I don't have any experience with it, or personal knowledge that says that this is true)

Also (but this is a different thing) :
See : https://en.wikipedia.org/wiki/Dnsmasq
You will find plenty of descriptions of dnsmasq on the WWW, but as a short primer :
- dnsmasq runs as a daemon on you local system, and listens for DNS requests on 127.0.0.1:53
- the "DNS resolver" on your localhost is configured to "ask" dnsmasq first, whenever an 
application has a DNS query
- when dnsmasq receives a DNS query, it consults its local cache first, then the local 
"hosts" file, and then (if it does not find the answer there), itself is configured to ask

one or more external DNS servers. (and if it gets a result from there, it puts it in its 
local cache, for a while).

> But isn't this addr a loopback IP? I was not sure about it.
> I was thinking the caching server should be 8.8.8.8 etc.
>
>>
>>> (base) pyh@ubuntu-18:~$ dig google.com.hk
>>>
>>> ; <<>> DiG 9.11.3-1ubuntu1.5-Ubuntu <<>> google.com.hk
>>> ;; global options: +cmd
>>> ;; Got answer:
>>> ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 58759
>>> ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
>>>
>>> ;; OPT PSEUDOSECTION:
>>> ; EDNS: version: 0, flags:; udp: 65494
>>> ;; QUESTION SECTION:
>>> ;google.com.hk.                 IN      A
>>>
>>> ;; ANSWER SECTION:
>>> google.com.hk.          22      IN      A       172.217.31.131
>>>
>>> ;; Query time: 1 msec
>>> ;; SERVER: 127.0.0.53#53(127.0.0.53)
>>> ;; WHEN: Mon Aug 05 19:48:49 CST 2019
>>> ;; MSG SIZE  rcvd: 58
>>>
>>>
>>> Can you help with it? thanks in advance.
>>
>> Help with what exactly? What is wrong with this DNS reply for you?
>> Seems totally legit.
>>
>
> what the helps I asked is that this server (127.0.0.53) returns many timeout during my
> modperl querying process.
>
> I think I may ask the sysadmin to add more caching servers and make them have good network
> connection with internet, am I right?
>
> thanks & regards.
> Paulina


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