I randomly have the problem on my 15.04 that the Internet connection via LAN stops working. This often happens directly after boot, but sometimes also just in the middle of a surfing session without any special actions.

My applications (Firefox, Skype, ...) report no network access, and both ping google.com and ping 8.8.8.8 also give up, as well as pinging my router (ping 192.168.0.1).

What I do if this connection loss is happening is that I click on the network indicator and select "Disconnect", wait a second and reconnect the same connection. After this procedure everything seems fine again.

Today it also went away by itself after some minutes, but some more connection breaks followed.

How can I troubleshoot this problem? What do I have to observe when it occurs next time to give you the important information? How will I finally be able to prevent such connection losses or can I at least have a workaround that automatically detects and solves it?

Update 1:

$ sudo lshw -C network

  *-network               

       description: Ethernet interface

       product: 82573L Gigabit Ethernet Controller

       vendor: Intel Corporation

       physical id: 0

       bus info: pci@0000:02:00.0

       logical name: eth0

       version: 00

       serial: 00:17:31:a1:f5:fa

       size: 100Mbit/s

       capacity: 1Gbit/s

       width: 32 bits

       clock: 33MHz

       capabilities: pm msi pciexpress bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation

       configuration: autonegotiation=on broadcast=yes driver=e1000e driverversion=2.3.2-k duplex=full firmware=0.5-7 ip=192.168.0.107 latency=0 link=yes multicast=yes port=twisted pair speed=100Mbit/s

       resources: irq:24 memory:cfee0000-cfefffff ioport:c800(size=32)

Update 2:

Content of /var/log/syslog around the time of the last connection failure:

Jul 12 16:14:23 MaxData-Desktop-Ubuntu kernel: [ 5298.718729] [UFW BLOCK] IN=eth0 OUT= MAC=01:00:5e:00:00:01:24:65:11:25:b0:0c:08:00 SRC=192.168.0.1 DST=224.0.0.1 LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 DF PROTO=2 

Jul 12 16:15:07 MaxData-Desktop-Ubuntu whoopsie[670]: [16:15:07] Cannot reach: https://daisy.ubuntu.com

Jul 12 16:15:07 MaxData-Desktop-Ubuntu whoopsie[670]: [16:15:07] offline

Jul 12 16:15:27 MaxData-Desktop-Ubuntu whoopsie[670]: [16:15:27] Cannot reach: https://daisy.ubuntu.com

Jul 12 16:15:47 MaxData-Desktop-Ubuntu whoopsie[670]: [16:15:47] Cannot reach: https://daisy.ubuntu.com

Jul 12 16:16:07 MaxData-Desktop-Ubuntu whoopsie[670]: [16:16:07] Cannot reach: https://daisy.ubuntu.com

Jul 12 16:16:28 MaxData-Desktop-Ubuntu kernel: [ 5423.720176] [UFW BLOCK] IN=eth0 OUT= MAC=01:00:5e:00:00:01:24:65:11:25:b0:0c:08:00 SRC=192.168.0.1 DST=224.0.0.1 LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 DF PROTO=2 

Jul 12 16:16:30 MaxData-Desktop-Ubuntu whoopsie[670]: [16:16:30] Cannot reach: https://daisy.ubuntu.com

Jul 12 16:16:50 MaxData-Desktop-Ubuntu whoopsie[670]: [16:16:50] Cannot reach: https://daisy.ubuntu.com

Jul 12 16:17:01 MaxData-Desktop-Ubuntu CRON[9122]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)

Jul 12 16:17:10 MaxData-Desktop-Ubuntu whoopsie[670]: [16:17:10] Cannot reach: https://daisy.ubuntu.com

Jul 12 16:18:33 MaxData-Desktop-Ubuntu kernel: [ 5548.718565] [UFW BLOCK] IN=eth0 OUT= MAC=01:00:5e:00:00:01:24:65:11:25:b0:0c:08:00 SRC=192.168.0.1 DST=224.0.0.1 LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 DF PROTO=2 

Jul 12 16:20:38 MaxData-Desktop-Ubuntu kernel: [ 5673.717889] [UFW BLOCK] IN=eth0 OUT= MAC=01:00:5e:00:00:01:24:65:11:25:b0:0c:08:00 SRC=192.168.0.1 DST=224.0.0.1 LEN=36 TOS=0x00 PREC=0xC0 TTL=1 ID=0 DF PROTO=2 

Jul 12 15:12:48 MaxData-Desktop-Ubuntu gnome-session[6329]: message repeated 2 times: [ debconf: DbDriver "passwords" warning: could not open /var/cache/debconf/passwords.dat: Keine Berechtigung]

Jul 12 16:21:53 MaxData-Desktop-Ubuntu gnome-session[6329]: (process:9144): GLib-CRITICAL **: g_slice_set_config: assertion 'sys_page_size == 0' failed

Jul 12 16:22:23 MaxData-Desktop-Ubuntu whoopsie[670]: [16:22:23] online

Jul 12 16:22:23 MaxData-Desktop-Ubuntu kernel: [ 5778.310686] [UFW BLOCK] IN=eth0 OUT= MAC=00:17:31:a1:f5:fa:24:65:11:25:b0:0c:08:00 SRC=198.252.206.25 DST=192.168.0.107 LEN=110 TOS=0x00 PREC=0x00 TTL=50 ID=50591 DF PROTO=TCP SPT=443 DPT=54409 WINDOW=33 RES=0x00 ACK PSH URGP=0 

Before and after this snippet are more [UFW BLOCK] lines, but they don't seem suspicious to me. I have similar lines in dmesg, but nothing more.