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dlangille/1 - background

Created October 25, 2023 01:08
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Let's test the timeout option for /etc/resolv.conf (note host(8) is not a valid test; it does not honor options)
Raw
1 - background
I have N nameservers. If one, or more, of them are down, I still want DNS to resolve quickly.
I could use carp or vrrp. But I'm not there yet.
The pro of carp/vrrp - no changes to clients.
THe pro of /etc/resolv.conf - don't have to set up carp/vrrp - easy to test
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1 - testing with options and all NS working
% cat /etc/resolv.conf
#nameserver 10.55.0.124
nameserver 10.55.0.1
options attempts:1 timeout:1 reload-period:0
% time ping -c1 google.com
PING google.com (142.251.40.174): 56 data bytes
64 bytes from 142.251.40.174: icmp_seq=0 ttl=119 time=7.687 ms
--- google.com ping statistics ---
1 packets transmitted, 1 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 7.687/7.687/7.687/0.000 ms
ping -c1 google.com 0.00s user 0.00s system 20% cpu 0.013 total
Very fast
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2 - testing with options and and NS down
% # there is no nameserver at 10.55.0.124, to simulate an offline host
% cat /etc/resolv.conf
nameserver 10.55.0.124
nameserver 10.55.0.1
options attempts:1 timeout:1 reload-period:0
% time ping -c1 google.com
PING google.com (142.251.40.174): 56 data bytes
64 bytes from 142.251.40.174: icmp_seq=0 ttl=119 time=9.443 ms
--- google.com ping statistics ---
1 packets transmitted, 1 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 9.443/9.443/9.443/0.000 ms
ping -c1 google.com 0.00s user 0.00s system 0% cpu 3.252 total
3.2 seconds to time out and try the next host.
Raw
3 - testing without options and an NS down
% cat /etc/resolv.conf
nameserver 10.55.0.124
nameserver 10.55.0.1
#options attempts:1 timeout:1 reload-period:0
% time ping -c1 google.com
PING google.com (142.251.40.174): 56 data bytes
64 bytes from 142.251.40.174: icmp_seq=0 ttl=119 time=8.725 ms
--- google.com ping statistics ---
1 packets transmitted, 1 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 8.725/8.725/8.725/0.000 ms
ping -c1 google.com 0.00s user 0.00s system 0% cpu 15.610 total
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