Linux: How to dealt with unstable network connection

Table of Contents

This is a guide for troubleshooting an unstable network (Ethernet) issue I experienced while using Lubuntu. The problem occurred with occasional disconnections, requiring me to manually reconnect each time.

Environment

Ubuntu 16.04 LTS
Lev-15FX088-i7-VE, Stl-13FH051-P-CE (Pc-Koubou PC)
Ethernet controller: Qualcomm Atheros Killer E2400 Gigabit Ethernet Controller (rev 10)

Background

I was using the company’s LAN connection, but the network occasionally got disconnected, forcing me to reconnect each time. To find a permanent solution, I investigated the issue.

Investigation Results

I used the dmesg command for investigation, but I couldn’t find anything particularly unusual. Then, I executed tail -f /var/log/syslog to monitor the log, and found the following output:

Jun 24 09:38:11 P750DM dhclient[4701]: XMT: Info-Request on enp66s9, interval 1080ms.
Jun 24 09:38:11 P750DM dhclient[4701]: RCV: Reply message on enp66s9 from ffff::aaaa:bbbb:cccc:dddd.
Jun 24 09:38:11 P750DM NetworkManager[738]: <info>  [1466728691.2427]   nameserver '2222:3333:4444:5555::6666'
Jun 24 09:38:11 P750DM NetworkManager[738]: <info>  [1466728691.2427]   nameserver '2222:3333:4444:5555::6666'
Jun 24 09:38:11 P750DM NetworkManager[738]: <info>  [1466728691.2428]   domain search 'flets-east.jp.'
Jun 24 09:38:11 P750DM NetworkManager[738]: <info>  [1466728691.2428]   domain search 'iptvf.jp.'
Jun 24 09:38:11 P750DM NetworkManager[738]: <info>  [1466728691.2428] dhcp6 (enp66s9): state changed unknown -> bound
Jun 24 09:38:11 P750DM NetworkManager[738]: <info>  [1466728691.2436] dhcp6 (enp66s9): client pid 4701 exited with status 0
Jun 24 09:38:11 P750DM NetworkManager[738]: <info>  [1466728691.2436] dhcp6 (enp66s9): state changed bound -> done
Jun 24 09:38:11 P750DM NetworkManager[738]: <info>  [1466728691.2449] dns-mgr: Writing DNS information to /sbin/resolvconf
Jun 24 09:38:11 P750DM dnsmasq[928]: setting upstream servers from DBus
Jun 24 09:38:11 P750DM dnsmasq[928]: using nameserver 2404:1a8:7f01:b::3#53
Jun 24 09:38:11 P750DM dnsmasq[928]: using nameserver 2404:1a8:7f01:a::3#53
Jun 24 09:38:11 P750DM dnsmasq[928]: using nameserver 192.168.1.1#53
Jun 24 09:38:11 P750DM nm-dispatcher: req:3 'dhcp6-change' [enp66s9]: new request (1 scripts)
Jun 24 09:38:11 P750DM nm-dispatcher: req:3 'dhcp6-change' [enp66s9]: start running ordered scripts...
Jun 24 09:38:12 P750DM ntpd[1073]: bind(23) AF_INET6 1111:2222:3333:4444:5555:6666:7777:8888#123 flags 0x11 failed: Cannot assign requested address
Jun 24 09:38:12 P750DM ntpd[1073]: unable to create socket on enp66s9 (40) for 2408:210:ac08:3400:69b3:d889:12ed:22d8#123
Jun 24 09:38:12 P750DM ntpd[1073]: failed to init interface for address 2408:210:ac08:3400:69b3:d889:12ed:22d8
Jun 24 09:38:12 P750DM ntpd[1073]: bind(23) AF_INET6 2222:3333:4444:5555:6666:7777:8888:9999#123 flags 0x11 failed: Cannot assign requested address
Jun 24 09:38:12 P750DM ntpd[1073]: unable to create socket on enp66s9 (41) for 2408:210:ac08:3400:98a1:d90e:e9a:4c1d#123
Jun 24 09:38:12 P750DM ntpd[1073]: failed to init interface for address 2408:210:ac08:3400:98a1:d90e:e9a:4c1d
Jun 24 09:38:22 P750DM ntpd[1073]: Listen normally on 42 enp66s9 [3333:4444:5555:6666:7777:8888:9999:0000]:123
Jun 24 09:38:22 P750DM ntpd[1073]: Listen normally on 43 enp66s9 [4444:5555:6666:7777:8888:9999:0000:1111]:123
Jun 24 09:38:22 P750DM ntpd[1073]: new interface(s) found: waking up resolver
Jun 24 09:38:30 P750DM NetworkManager[738]: <warn>  [1466728710.1338] device (enp66s9): disconnecting connection 'Wired connection 2' for new activation request.
Jun 24 09:38:30 P750DM NetworkManager[738]: <info>  [1466728710.1339] device (enp66s9): state change: activated -> deactivating (reason 'new-activation') [100 110 60]
Jun 24 09:38:30 P750DM NetworkManager[738]: <info>  [1466728710.1341] manager: NetworkManager state is now DISCONNECTING
Jun 24 09:38:30 P750DM whoopsie[735]: [09:38:30] offline
Jun 24 09:38:30 P750DM NetworkManager[738]: <info>  [1466728710.1815] device (enp66s9): disconnecting for new activation request.
Jun 24 09:38:30 P750DM NetworkManager[738]: <info>  [1466728710.1817] audit: op="connection-activate" uuid="11111111-2222-3333-4444-555555555555" name="Wired connection 2" pid=1715 uid=1000 result="success"
Jun 24 09:38:30 P750DM NetworkManager[738]: <info>  [1466728710.1831] device (enp66s9): state change: deactivating -> disconnected (reason 'new-activation') [110 30 60]
Jun 24 09:38:30 P750DM NetworkManager[738]: <info>  [1466728710.1848] dhcp4 (enp66s9): canceled DHCP transaction, DHCP client pid 4589
Jun 24 09:38:30 P750DM NetworkManager[738]: <info>  [1466728710.1848] dhcp4 (enp66s9): state changed bound -> done
Jun 24 09:38:30 P750DM NetworkManager[738]: <info>  [1466728710.1853] dhcp6 (enp66s9): canceled DHCP transaction
Jun 24 09:38:30 P750DM NetworkManager[738]: <info>  [1466728710.1866] dns-mgr: Writing DNS information to /sbin/resolvconf

Jun 24 09:38:11 P750DM dhclient[4701]: XMT: Info-Request on enp66s9, interval 1080ms.

Jun 24 09:38:11 P750DM dhclient[4701]: RCV: Reply message on enp66s9 from ffff::aaaa:bbbb:cccc:dddd.

Jun 24 09:38:11 P750DM NetworkManager[738]: <info> [1466728691.2427] nameserver '2222:3333:4444:5555::6666'

Jun 24 09:38:11 P750DM NetworkManager[738]: <info> [1466728691.2428] domain search 'flets-east.jp.'

Jun 24 09:38:11 P750DM NetworkManager[738]: <info> [1466728691.2428] domain search 'iptvf.jp.'

Jun 24 09:38:11 P750DM NetworkManager[738]: <info> [1466728691.2428] dhcp6 (enp66s9): state changed unknown -> bound

Jun 24 09:38:11 P750DM NetworkManager[738]: <info> [1466728691.2436] dhcp6 (enp66s9): client pid 4701 exited with status 0

Jun 24 09:38:11 P750DM NetworkManager[738]: <info> [1466728691.2436] dhcp6 (enp66s9): state changed bound -> done

Jun 24 09:38:11 P750DM NetworkManager[738]: <info> [1466728691.2449] dns-mgr: Writing DNS information to /sbin/resolvconf

Jun 24 09:38:11 P750DM dnsmasq[928]: setting upstream servers from DBus

Jun 24 09:38:11 P750DM dnsmasq[928]: using nameserver 2404:1a8:7f01:b::3#53

Jun 24 09:38:11 P750DM dnsmasq[928]: using nameserver 2404:1a8:7f01:a::3#53

Jun 24 09:38:11 P750DM dnsmasq[928]: using nameserver 192.168.1.1#53

Jun 24 09:38:11 P750DM nm-dispatcher: req:3 'dhcp6-change' [enp66s9]: new request (1 scripts)

Jun 24 09:38:11 P750DM nm-dispatcher: req:3 'dhcp6-change' [enp66s9]: start running ordered scripts...

Jun 24 09:38:12 P750DM ntpd[1073]: bind(23) AF_INET6 1111:2222:3333:4444:5555:6666:7777:8888#123 flags 0x11 failed: Cannot assign requested address

Jun 24 09:38:12 P750DM ntpd[1073]: unable to create socket on enp66s9 (40) for 2408:210:ac08:3400:69b3:d889:12ed:22d8#123

Jun 24 09:38:12 P750DM ntpd[1073]: failed to init interface for address 2408:210:ac08:3400:69b3:d889:12ed:22d8

Jun 24 09:38:12 P750DM ntpd[1073]: bind(23) AF_INET6 2222:3333:4444:5555:6666:7777:8888:9999#123 flags 0x11 failed: Cannot assign requested address

Jun 24 09:38:12 P750DM ntpd[1073]: unable to create socket on enp66s9 (41) for 2408:210:ac08:3400:98a1:d90e:e9a:4c1d#123

Jun 24 09:38:12 P750DM ntpd[1073]: failed to init interface for address 2408:210:ac08:3400:98a1:d90e:e9a:4c1d

Jun 24 09:38:22 P750DM ntpd[1073]: Listen normally on 42 enp66s9 [3333:4444:5555:6666:7777:8888:9999:0000]:123

Jun 24 09:38:22 P750DM ntpd[1073]: Listen normally on 43 enp66s9 [4444:5555:6666:7777:8888:9999:0000:1111]:123

Jun 24 09:38:22 P750DM ntpd[1073]: new interface(s) found: waking up resolver

Jun 24 09:38:30 P750DM NetworkManager[738]: <warn> [1466728710.1338] device (enp66s9): disconnecting connection 'Wired connection 2' for new activation request.

Jun 24 09:38:30 P750DM NetworkManager[738]: <info> [1466728710.1339] device (enp66s9): state change: activated -> deactivating (reason 'new-activation') [100 110 60]

Jun 24 09:38:30 P750DM NetworkManager[738]: <info> [1466728710.1341] manager: NetworkManager state is now DISCONNECTING

Jun 24 09:38:30 P750DM whoopsie[735]: [09:38:30] offline

Jun 24 09:38:30 P750DM NetworkManager[738]: <info> [1466728710.1815] device (enp66s9): disconnecting for new activation request.

Jun 24 09:38:30 P750DM NetworkManager[738]: <info> [1466728710.1817] audit: op="connection-activate" uuid="11111111-2222-3333-4444-555555555555" name="Wired connection 2" pid=1715 uid=1000 result="success"

Jun 24 09:38:30 P750DM NetworkManager[738]: <info> [1466728710.1831] device (enp66s9): state change: deactivating -> disconnected (reason 'new-activation') [110 30 60]

Jun 24 09:38:30 P750DM NetworkManager[738]: <info> [1466728710.1848] dhcp4 (enp66s9): canceled DHCP transaction, DHCP client pid 4589

Jun 24 09:38:30 P750DM NetworkManager[738]: <info> [1466728710.1848] dhcp4 (enp66s9): state changed bound -> done

Jun 24 09:38:30 P750DM NetworkManager[738]: <info> [1466728710.1853] dhcp6 (enp66s9): canceled DHCP transaction

Jun 24 09:38:30 P750DM NetworkManager[738]: <info> [1466728710.1866] dns-mgr: Writing DNS information to /sbin/resolvconf

Although I’m not an expert in Linux, I thought disabling IPv6 might resolve the issue.

Solution

First, I added the following three lines to /etc/sysctl.conf:

net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1

net.ipv6.conf.all.disable_ipv6 = 1

net.ipv6.conf.default.disable_ipv6 = 1

net.ipv6.conf.lo.disable_ipv6 = 1

Then, I executed sudo sysctl -p to apply the changes, effectively disabling IPv6.

Reference: How to disable IPv6 in Ubuntu 14.04?

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