Why does *.localhost resolve to 127.0.0.1 and ::1?
Clash Royale CLAN TAG#URR8PPP
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I discovered by chance (trying to access a proxied service in a Docker container on a Vagrant box using servicename.docker.localhost from the host) that any hostname ending in ".localhost" resolves to 127.0.0.1 or ::1 on my machine:
$ ping -4 -c1 -n foo.localhost
PING localhost (127.0.0.1) 56(84) bytes of data.
64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.147 ms
--- localhost ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.147/0.147/0.147/0.000 ms
$ ping -6 -c1 -n foo.localhost
PING foo.localhost(::1) 56 data bytes
64 bytes from ::1: icmp_seq=1 ttl=64 time=0.072 ms
--- foo.localhost ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.072/0.072/0.072/0.000 ms
However, there is no DNS entry for this:
$ nslookup -type=AAAA foo.localhost
Server: 192.168.2.82
Address: 192.168.2.82#53
** server can't find foo.localhost: NXDOMAIN
$ nslookup -type=A foo.localhost
Server: 192.168.2.82
Address: 192.168.2.82#53
** server can't find foo.localhost: NXDOMAIN
/etc/hosts doesn't look particularly relevant:
127.0.0.1 my-machine-name.my-work-domain my-machine-name localhost.localdomain localhost
::1 localhost.localdomain localhost
Neither does /etc/resolv.conf:
domain my-work-domain
search my-work-domain
nameserver 192.[…]
nameserver 192.[…]
Why does *.localhost magically resolve?
This is similar but possibly distinct from this question.
$ getent hosts
127.0.0.1 my-machine-name.my-work-domain my-machine-name localhost.localdomain localhost
127.0.0.1 localhost.localdomain localhost
$ getent hosts foo.localhost
::1 localhost
arch-linux dns
asked May 27 at 23:34
l0b0
26k17104226
add a comment |Â
up vote
3
down vote
favorite
I discovered by chance (trying to access a proxied service in a Docker container on a Vagrant box using servicename.docker.localhost from the host) that any hostname ending in ".localhost" resolves to 127.0.0.1 or ::1 on my machine:
$ ping -4 -c1 -n foo.localhost
PING localhost (127.0.0.1) 56(84) bytes of data.
64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.147 ms
--- localhost ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.147/0.147/0.147/0.000 ms
$ ping -6 -c1 -n foo.localhost
PING foo.localhost(::1) 56 data bytes
64 bytes from ::1: icmp_seq=1 ttl=64 time=0.072 ms
--- foo.localhost ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.072/0.072/0.072/0.000 ms
However, there is no DNS entry for this:
$ nslookup -type=AAAA foo.localhost
Server: 192.168.2.82
Address: 192.168.2.82#53
** server can't find foo.localhost: NXDOMAIN
$ nslookup -type=A foo.localhost
Server: 192.168.2.82
Address: 192.168.2.82#53
** server can't find foo.localhost: NXDOMAIN
/etc/hosts doesn't look particularly relevant:
127.0.0.1 my-machine-name.my-work-domain my-machine-name localhost.localdomain localhost
::1 localhost.localdomain localhost
Neither does /etc/resolv.conf:
domain my-work-domain
search my-work-domain
nameserver 192.[…]
nameserver 192.[…]
Why does *.localhost magically resolve?
This is similar but possibly distinct from this question.
$ getent hosts
127.0.0.1 my-machine-name.my-work-domain my-machine-name localhost.localdomain localhost
127.0.0.1 localhost.localdomain localhost
$ getent hosts foo.localhost
::1 localhost
arch-linux dns
asked May 27 at 23:34
l0b0
26k17104226
What doesgetentsay?
– Ignacio Vazquez-Abrams
May 28 at 0:16
Are you using systemd? It has a last resort resolver that (if none other nameserver resolved it before) resolves localhost to::1.
– Isaac
May 28 at 9:04
@Isaac I think you can write that as an answer. From the page you linked to: "systemd-resolved synthesizes DNS resource records (RRs) for the following cases: [...] any hostname ending in ".localhost" or ".localhost.localdomain") are resolved to the IP addresses 127.0.0.1 and ::1"
– Johan Myréen
May 28 at 15:47
Also just FYI, before/etc/resolv.confand/etc/hoststhere is/etc/nsswitch.confwhich controls what sources the libc resolver uses, and in what order.grep '^hosts:' /etc/nsswitch.conf.
– Patrick
May 28 at 19:54
add a comment |Â
up vote
3
down vote
favorite
up vote
3
down vote
favorite
I discovered by chance (trying to access a proxied service in a Docker container on a Vagrant box using servicename.docker.localhost from the host) that any hostname ending in ".localhost" resolves to 127.0.0.1 or ::1 on my machine:
$ ping -4 -c1 -n foo.localhost
PING localhost (127.0.0.1) 56(84) bytes of data.
64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.147 ms
--- localhost ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.147/0.147/0.147/0.000 ms
$ ping -6 -c1 -n foo.localhost
PING foo.localhost(::1) 56 data bytes
64 bytes from ::1: icmp_seq=1 ttl=64 time=0.072 ms
--- foo.localhost ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.072/0.072/0.072/0.000 ms
However, there is no DNS entry for this:
$ nslookup -type=AAAA foo.localhost
Server: 192.168.2.82
Address: 192.168.2.82#53
** server can't find foo.localhost: NXDOMAIN
$ nslookup -type=A foo.localhost
Server: 192.168.2.82
Address: 192.168.2.82#53
** server can't find foo.localhost: NXDOMAIN
/etc/hosts doesn't look particularly relevant:
127.0.0.1 my-machine-name.my-work-domain my-machine-name localhost.localdomain localhost
::1 localhost.localdomain localhost
Neither does /etc/resolv.conf:
domain my-work-domain
search my-work-domain
nameserver 192.[…]
nameserver 192.[…]
Why does *.localhost magically resolve?
This is similar but possibly distinct from this question.
$ getent hosts
127.0.0.1 my-machine-name.my-work-domain my-machine-name localhost.localdomain localhost
127.0.0.1 localhost.localdomain localhost
$ getent hosts foo.localhost
::1 localhost
arch-linux dns
asked May 27 at 23:34
l0b0
26k17104226
I discovered by chance (trying to access a proxied service in a Docker container on a Vagrant box using servicename.docker.localhost from the host) that any hostname ending in ".localhost" resolves to 127.0.0.1 or ::1 on my machine:
$ ping -4 -c1 -n foo.localhost
PING localhost (127.0.0.1) 56(84) bytes of data.
64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.147 ms
--- localhost ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.147/0.147/0.147/0.000 ms
$ ping -6 -c1 -n foo.localhost
PING foo.localhost(::1) 56 data bytes
64 bytes from ::1: icmp_seq=1 ttl=64 time=0.072 ms
--- foo.localhost ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.072/0.072/0.072/0.000 ms
However, there is no DNS entry for this:
$ nslookup -type=AAAA foo.localhost
Server: 192.168.2.82
Address: 192.168.2.82#53
** server can't find foo.localhost: NXDOMAIN
$ nslookup -type=A foo.localhost
Server: 192.168.2.82
Address: 192.168.2.82#53
** server can't find foo.localhost: NXDOMAIN
/etc/hosts doesn't look particularly relevant:
127.0.0.1 my-machine-name.my-work-domain my-machine-name localhost.localdomain localhost
::1 localhost.localdomain localhost
Neither does /etc/resolv.conf:
domain my-work-domain
search my-work-domain
nameserver 192.[…]
nameserver 192.[…]
Why does *.localhost magically resolve?
This is similar but possibly distinct from this question.
$ getent hosts
127.0.0.1 my-machine-name.my-work-domain my-machine-name localhost.localdomain localhost
127.0.0.1 localhost.localdomain localhost
$ getent hosts foo.localhost
::1 localhost
arch-linux dns
asked May 27 at 23:34
l0b0
26k17104226
edited May 28 at 3:39
asked May 27 at 23:34
l0b0
26k17104226
asked May 27 at 23:34
l0b0
26k17104226
asked May 27 at 23:34
l0b0
26k17104226
26k17104226
What doesgetentsay?
– Ignacio Vazquez-Abrams
May 28 at 0:16
Are you using systemd? It has a last resort resolver that (if none other nameserver resolved it before) resolves localhost to::1.
– Isaac
May 28 at 9:04
@Isaac I think you can write that as an answer. From the page you linked to: "systemd-resolved synthesizes DNS resource records (RRs) for the following cases: [...] any hostname ending in ".localhost" or ".localhost.localdomain") are resolved to the IP addresses 127.0.0.1 and ::1"
– Johan Myréen
May 28 at 15:47
Also just FYI, before/etc/resolv.confand/etc/hoststhere is/etc/nsswitch.confwhich controls what sources the libc resolver uses, and in what order.grep '^hosts:' /etc/nsswitch.conf.
– Patrick
May 28 at 19:54
add a comment |Â
What doesgetentsay?
– Ignacio Vazquez-Abrams
May 28 at 0:16
Are you using systemd? It has a last resort resolver that (if none other nameserver resolved it before) resolves localhost to::1.
– Isaac
May 28 at 9:04
@Isaac I think you can write that as an answer. From the page you linked to: "systemd-resolved synthesizes DNS resource records (RRs) for the following cases: [...] any hostname ending in ".localhost" or ".localhost.localdomain") are resolved to the IP addresses 127.0.0.1 and ::1"
– Johan Myréen
May 28 at 15:47
Also just FYI, before/etc/resolv.confand/etc/hoststhere is/etc/nsswitch.confwhich controls what sources the libc resolver uses, and in what order.grep '^hosts:' /etc/nsswitch.conf.
– Patrick
May 28 at 19:54
What does
getent say?– Ignacio Vazquez-Abrams
May 28 at 0:16
What does
getent say?– Ignacio Vazquez-Abrams
May 28 at 0:16
Are you using systemd? It has a last resort resolver that (if none other nameserver resolved it before) resolves localhost to
::1.– Isaac
May 28 at 9:04
Are you using systemd? It has a last resort resolver that (if none other nameserver resolved it before) resolves localhost to
::1.– Isaac
May 28 at 9:04
@Isaac I think you can write that as an answer. From the page you linked to: "systemd-resolved synthesizes DNS resource records (RRs) for the following cases: [...] any hostname ending in ".localhost" or ".localhost.localdomain") are resolved to the IP addresses 127.0.0.1 and ::1"
– Johan Myréen
May 28 at 15:47
@Isaac I think you can write that as an answer. From the page you linked to: "systemd-resolved synthesizes DNS resource records (RRs) for the following cases: [...] any hostname ending in ".localhost" or ".localhost.localdomain") are resolved to the IP addresses 127.0.0.1 and ::1"
– Johan Myréen
May 28 at 15:47
Also just FYI, before
/etc/resolv.conf and /etc/hosts there is /etc/nsswitch.conf which controls what sources the libc resolver uses, and in what order. grep '^hosts:' /etc/nsswitch.conf.– Patrick
May 28 at 19:54
Also just FYI, before
/etc/resolv.conf and /etc/hosts there is /etc/nsswitch.conf which controls what sources the libc resolver uses, and in what order. grep '^hosts:' /etc/nsswitch.conf.– Patrick
May 28 at 19:54
add a comment |Â
1 Answer
1
active
oldest
votes
up vote
3
down vote
accepted
This is caused by the myhostname NSS module which defines the hostname and any name ending in .localhost as 127.0.0.1 in ipv4 and ::1 in ipv6.
https://www.freedesktop.org/software/systemd/man/nss-myhostname.html
answered May 28 at 20:48
jdwolf
2,362116
nss-systemd could theoretically do something similar but not only is Arch Linux not configured like this by default nor is systemd.
– jdwolf
May 28 at 20:49
You nailed it - /etc/nsswitch.conf enablesmyhostname.
– l0b0
May 28 at 20:58
add a comment |Â
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
3
down vote
accepted
This is caused by the myhostname NSS module which defines the hostname and any name ending in .localhost as 127.0.0.1 in ipv4 and ::1 in ipv6.
https://www.freedesktop.org/software/systemd/man/nss-myhostname.html
answered May 28 at 20:48
jdwolf
2,362116
nss-systemd could theoretically do something similar but not only is Arch Linux not configured like this by default nor is systemd.
– jdwolf
May 28 at 20:49
You nailed it - /etc/nsswitch.conf enablesmyhostname.
– l0b0
May 28 at 20:58
add a comment |Â
up vote
3
down vote
accepted
This is caused by the myhostname NSS module which defines the hostname and any name ending in .localhost as 127.0.0.1 in ipv4 and ::1 in ipv6.
https://www.freedesktop.org/software/systemd/man/nss-myhostname.html
answered May 28 at 20:48
jdwolf
2,362116
nss-systemd could theoretically do something similar but not only is Arch Linux not configured like this by default nor is systemd.
– jdwolf
May 28 at 20:49
You nailed it - /etc/nsswitch.conf enablesmyhostname.
– l0b0
May 28 at 20:58
add a comment |Â
up vote
3
down vote
accepted
up vote
3
down vote
accepted
This is caused by the myhostname NSS module which defines the hostname and any name ending in .localhost as 127.0.0.1 in ipv4 and ::1 in ipv6.
https://www.freedesktop.org/software/systemd/man/nss-myhostname.html
answered May 28 at 20:48
jdwolf
2,362116
This is caused by the myhostname NSS module which defines the hostname and any name ending in .localhost as 127.0.0.1 in ipv4 and ::1 in ipv6.
https://www.freedesktop.org/software/systemd/man/nss-myhostname.html
answered May 28 at 20:48
jdwolf
2,362116
answered May 28 at 20:48
jdwolf
2,362116
answered May 28 at 20:48
jdwolf
2,362116
answered May 28 at 20:48
jdwolf
2,362116
2,362116
nss-systemd could theoretically do something similar but not only is Arch Linux not configured like this by default nor is systemd.
– jdwolf
May 28 at 20:49
You nailed it - /etc/nsswitch.conf enablesmyhostname.
– l0b0
May 28 at 20:58
add a comment |Â
nss-systemd could theoretically do something similar but not only is Arch Linux not configured like this by default nor is systemd.
– jdwolf
May 28 at 20:49
You nailed it - /etc/nsswitch.conf enablesmyhostname.
– l0b0
May 28 at 20:58
nss-systemd could theoretically do something similar but not only is Arch Linux not configured like this by default nor is systemd.
– jdwolf
May 28 at 20:49
nss-systemd could theoretically do something similar but not only is Arch Linux not configured like this by default nor is systemd.
– jdwolf
May 28 at 20:49
You nailed it - /etc/nsswitch.conf enables
myhostname.– l0b0
May 28 at 20:58
You nailed it - /etc/nsswitch.conf enables
myhostname.– l0b0
May 28 at 20:58
add a comment |Â
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What does
getentsay?– Ignacio Vazquez-Abrams
May 28 at 0:16
Are you using systemd? It has a last resort resolver that (if none other nameserver resolved it before) resolves localhost to
::1.– Isaac
May 28 at 9:04
@Isaac I think you can write that as an answer. From the page you linked to: "systemd-resolved synthesizes DNS resource records (RRs) for the following cases: [...] any hostname ending in ".localhost" or ".localhost.localdomain") are resolved to the IP addresses 127.0.0.1 and ::1"
– Johan Myréen
May 28 at 15:47
Also just FYI, before
/etc/resolv.confand/etc/hoststhere is/etc/nsswitch.confwhich controls what sources the libc resolver uses, and in what order.grep '^hosts:' /etc/nsswitch.conf.– Patrick
May 28 at 19:54