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Clear DNS configuration received from DHCP during networking reconfig…
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…uration in Linux. (#13516) (#13695)

- Why I did it
fixes #12907

When the management interface IP address configuration changes from dynamic to static the DNS configuration (retrieved from the DHCP server) in /etc/resolv.conf remains uncleared. This leads to a DNS configuration pointing to the wrong nameserver. To make the behavior clear DNS configuration received from DHCP should be cleared.

- How I did it
Use resolvconf package for managing DNS configuration. It is capable of tracking the source of DNS configuration and puts the configuration retrieved from the DHCP servers into a separate file. This allows the implementation of DNS configuration cleanup retrieved from DHCP during networking reconfiguration.

- How to verify it
Ensure that the management interface has no static configuration.
Check that /etc/resolv.conf has DNS configuration.
Configure a static IP address on the management interface.
Verify that /etc/resolv.conf has no DNS configuration.
Remove the static IP address from the management interface.
Verify that /etc/resolv.conf has DNS configuration retrieved form DHCP server.
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oleksandrivantsiv authored Feb 10, 2023
1 parent 7642f4c commit d1fa414
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Showing 4 changed files with 12 additions and 2 deletions.
9 changes: 7 additions & 2 deletions build_debian.sh
Original file line number Diff line number Diff line change
Expand Up @@ -385,7 +385,8 @@ sudo LANG=C DEBIAN_FRONTEND=noninteractive chroot $FILESYSTEM_ROOT apt-get -y in
gpg \
jq \
auditd \
linux-perf
linux-perf \
resolvconf

# Have systemd create the auditd log directory
sudo mkdir -p ${FILESYSTEM_ROOT}/etc/systemd/system/auditd.service.d
Expand Down Expand Up @@ -661,7 +662,11 @@ sudo rm -f $ONIE_INSTALLER_PAYLOAD $FILESYSTEM_SQUASHFS
## Note: -x to skip directories on different file systems, such as /proc
sudo du -hsx $FILESYSTEM_ROOT
sudo mkdir -p $FILESYSTEM_ROOT/var/lib/docker
sudo cp files/image_config/resolv-config/resolv.conf $FILESYSTEM_ROOT/etc/resolv.conf

## Clear DNS configuration inherited from the build server
sudo rm -f $FILESYSTEM_ROOT/etc/resolvconf/resolv.conf.d/original
sudo cp files/image_config/resolv-config/resolv.conf.head $FILESYSTEM_ROOT/etc/resolvconf/resolv.conf.d/head

sudo mksquashfs $FILESYSTEM_ROOT $FILESYSTEM_SQUASHFS -e boot -e var/lib/docker -e $PLATFORM_DIR

# Ensure admin gid is 1000
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3 changes: 3 additions & 0 deletions files/image_config/interfaces/interfaces-config.sh
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Expand Up @@ -60,6 +60,9 @@ for intf_pid in $(ls -1 /var/run/dhclient*.Ethernet*.pid 2> /dev/null); do
[[ -f ${intf_pid} ]] && kill `cat ${intf_pid}` && rm -f ${intf_pid}
done

[[ -f /var/run/resolvconf/interface/eth0.dhclient ]] && rm -f /var/run/resolvconf/interface/eth0.dhclient
[[ -f /var/run/resolvconf/interface/eth0.ip6.dhclient ]] && rm -f /var/run/resolvconf/interface/eth0.ip6.dhclient

# Read sysctl conf files again
sysctl -p /etc/sysctl.d/90-dhcp6-systcl.conf

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Empty file.
2 changes: 2 additions & 0 deletions files/image_config/resolv-config/resolv.conf.head
Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
# Dynamic resolv.conf(5) file generated by resolvconf(8)
# The content of this file may be overwritten during a config reload.

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