Re: [Bug-wget] strange behaviour

[Petr Pisar]

On Thu, May 10, 2018 at 10:27:35AM +0000, VINEETHSIVARAMAN wrote:
> My server is behind a firewall and a  proxy, but when i give  2 "wget" in
> command  gives me a DNS resolution but not with the single wget !
> 
[...]
> [~]$ nslookup google.com
> 
> Non-authoritative answer:
> Name:   google.com
> Address: 74.125.24.102
> Name:   google.com
> Address: 74.125.24.101
> Name:   google.com
> Address: 74.125.24.139
> Name:   google.com
> Address: 74.125.24.113
> Name:   google.com
> Address: 74.125.24.138
> Name:   google.com
> Address: 74.125.24.100
> 
> [~]$ wget google.com --no-proxy -d
> DEBUG output created by Wget 1.14 on linux-gnu.
> 
> URI encoding = ‘UTF-8’
> Converted file name 'index.html' (UTF-8) -> 'index.html' (UTF-8)
> Converted file name 'index.html' (UTF-8) -> 'index.html' (UTF-8)
> --2018-05-10 06:24:33--  http://google.com/
> Resolving google.com (google.com)... failed: Name or service not known.

nslookup bypasses system domain name resolver and querries DNS servers
directly comparing to wget or most of the other programs.

Do you experience the same issue with other programs that use system
resolver? E.g. "getent host google.com"? Maybe one of your name servers
misbehaves and only the second query to the second one succeeds. Maybe your
system resolved validates DNSSEC signatures and your network or name servers
block EDNS packets. What's your system resolver (/etc/nsswitch.conf), do you
use nscd or sssd caching deamons? If you do, what does happen if you flush
their caches (e.g. nscd --invalidate hosts). Capturing and studying network
packets while experiencing the issue would also help.

-- Petr

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