messages при отключении сети (eth0)
Feb 22 13:29:28 localhost net_applet[3223]: launched command: /usr/sbin/usernetctl eth0 report
Feb 22 13:29:28 localhost net_applet[3223]: running: consolehelper eth0
Feb 22 13:29:33 localhost avahi-daemon[2162]: Withdrawing address record for 192.168.1.33 on eth0.
Feb 22 13:29:33 localhost avahi-daemon[2162]: Leaving mDNS multicast group on interface eth0.IPv4 with address 192.168.1.33.
Feb 22 13:29:33 localhost avahi-daemon[2162]: Interface eth0.IPv4 no longer relevant for mDNS.
Feb 22 13:29:33 localhost avahi-daemon[2162]: querier.c: querier_remove() called but no querier to remove.
Feb 22 13:29:33 localhost last message repeated 3 times
Feb 22 13:29:34 localhost klogd: eth0: link up, 100Mbps, full-duplex, lpa 0x41E1
Feb 22 13:29:34 localhost mdkapplet[3214]: Checking Network: seems disabled

messages при включении сети (eth0)
Feb 22 13:30:31 localhost net_applet[3223]: launched command: /usr/sbin/usernetctl eth0 report
Feb 22 13:30:31 localhost net_applet[3223]: running: consolehelper eth0
Feb 22 13:30:35 localhost dhclient: DHCPREQUEST on eth0 to 255.255.255.255 port 67
Feb 22 13:30:35 localhost dhclient: DHCPACK from 192.168.1.1
Feb 22 13:30:35 localhost avahi-daemon[2162]: Joining mDNS multicast group on interface eth0.IPv4 with address 192.168.1.33.
Feb 22 13:30:35 localhost avahi-daemon[2162]: New relevant interface eth0.IPv4 for mDNS.
Feb 22 13:30:35 localhost avahi-daemon[2162]: Registering new address record for 192.168.1.33 on eth0.IPv4.
Feb 22 13:30:35 localhost NET[3924]: /sbin/dhclient-script : updated /etc/resolv.conf
Feb 22 13:30:35 localhost dhclient: bound to 192.168.1.33 -- renewal in 118012 seconds.
Feb 22 13:30:36 localhost mdkapplet[3214]: Computing new updates...
Feb 22 13:30:36 localhost mdkapplet[3214]: running: urpmi.update --update
Feb 22 13:30:46 localhost mdkapplet[3214]: updating inactive backport media Main Backports, Contrib Backports, Non-free Backports, PLF Free backports, PLF Non-free backports
Feb 22 13:30:46 localhost mdkapplet[3214]: running: urpmi.update Main Backports
Feb 22 13:30:47 localhost mdkapplet[3214]: running: urpmi.update Contrib Backports
Feb 22 13:30:49 localhost mdkapplet[3214]: running: urpmi.update Non-free Backports
Feb 22 13:30:50 localhost mdkapplet[3214]: running: urpmi.update PLF Free backports
Feb 22 13:30:52 localhost mdkapplet[3214]: running: urpmi.update PLF Non-free backports
Feb 22 13:30:54 localhost mdkapplet[3214]: Packages are up to date

Проверку сетевой карты отключил. Не помогло.

Проблема решена. Зависание интернет-соединения было из-за одновременной работы IPTV. Провайдер ЮТК (Волгоград), оказывается, не гарантирует стабильную работу двух одновременных соединений через один модем. Когда отключаю в настройках DSL-модема дополнительное интернет-соединение, все зависания основного соединения прекращаются - интернет летает.