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Date: Thu, 07 Jul 2022 18:16:41 +0000
From: Felix Tailor <felix.tailor@...me>
To: "musl@...ts.openwall.com" <musl@...ts.openwall.com>
Subject: resolv.conf misconfiguration, Round-Robin bug in musl or something else?
Hello,
I have encountered an issue when trying to resolve hosts that have multiple IPv4 addresses: I get the same IPv4 address for the host. I use ping or wget from busybox, which is linked against musl.
The issue occurs when there are IPv4 and IPv6 nameservers in resolv.conf. If I leave only one nameserver (IPv4 or IPv6), I get different IPv4 values (Round-Robin) as expected.
To reproduce this issue:
1. Install Docker and enable IPv6: https://docs.docker.com/config/daemon/ipv6/
2. Execute:
docker run --rm -it alpine:3.16.0 sh
apk add --no-cache dnsmasq
cat <<EOF >/etc/resolv.conf
nameserver 127.0.0.1
nameserver ::1
EOF
cat <<EOF >/etc/dnsmasq.conf
addn-hosts=/etc/addn-hosts
local=/lan/
EOF
cat <<EOF >/etc/addn-hosts
127.1.1.1 local.lan
127.2.2.2 local.lan
EOF
dnsmasq -C /etc/dnsmasq.conf -d &
i=0; while [ $i -lt 3 ]; do ping -qc1 local.lan; i=$((i+1)); done
PING local.lan (127.1.1.1) 56(84) bytes of data.
--- local.lan ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.006/0.006/0.006/0.000 ms
PING local.lan (127.1.1.1) 56(84) bytes of data.
--- local.lan ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.004/0.004/0.004/0.000 ms
PING local.lan (127.1.1.1) 56(84) bytes of data.
--- local.lan ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.004/0.004/0.004/0.000 ms
Ping always returns the same IPv4 address, but with nslookup different IPv4 addresses are returned, so Round-Robin seems to work:
root@...d4fb49d34:/# nslookup local.lan
Server: 127.0.0.1
Address: 127.0.0.1#53
Name: local.lan
Address: 127.1.1.1
Name: local.lan
Address: 127.2.2.2
root@...d4fb49d34:/# nslookup local.lan
Server: 127.0.0.1
Address: 127.0.0.1#53
Name: local.lan
Address: 127.2.2.2
Name: local.lan
Address: 127.1.1.1
root@...d4fb49d34:/# nslookup local.lan
Server: 127.0.0.1
Address: 127.0.0.1#53
Name: local.lan
Address: 127.1.1.1
Name: local.lan
Address: 127.2.2.2
Questions:
1. Why is Round-Robin not working with musl for hosts with multiple IPv4 addresses when using multiple different IP protocol nameservers in resolv.conf?
2. Is it reasonable to have multiple different IP protocol nameservers for localhost in resolv.conf?
3. Is replacing the contents of resolv.conf in this example with 'nameserver localhost' a viable solution?
Regards,
Felix
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