Hello,
I have a TP-Link N600 (TP-Link TL-WDR3600 v1.5) router with OpenWrt Barrier Breaker 14.07. Our Internet provider is primacom (tv-cable with Tomson cable-modem).
In the last weeks I'm frequently experiencing the following behavior:
I restart the router, after several minutes (~ 10 min) the Internet connection through the router drops. If I restart the router again, I will have Internet-Connection again, but it drops after several minutes again. If I restart the cable-modem and the router it is the same scenario.
While If I directly connect the computer to the cable-modem (without the OpenWrt router in between) I'll have constant Internet connection. (I always have to restart the cable-modem before I can connect a new device.)
The problem is, that this issue is not very predictable, once in between the Internet connection worked for a week (or maybe even two) and than I started to have this issue again.

Is there anything I could monitor to find the reason for this problem? I couldn't find anything suspicious in dmergs at the point of the loose-of connection so far.

Thank you
white_gecko

Try editing:

/etc/config/network

With the broadcast option to see if it resolves your issues. 0 is disabled and 1 is enabled.

config interface 'wan'
        option ifname 'eth0.2'
        option proto 'dhcp'
        option peerdns '0'
        option dns '8.8.8.8 8.8.4.4'
        option broadcast '1'

Thank you @kgoerbig for your answer and sorry for my late reply.

I've added the broadcast option to my network configuration (printed below). But what does this option actually do? And did I put it in the right place?

config interface 'loopback'
    option ifname 'lo'
    option proto 'static'
    option ipaddr '127.0.0.1'
    option netmask '255.0.0.0'

config globals 'globals'
    option ula_prefix 'fdd3:a28a:36a3::/48'

config interface 'lan'
    option ifname 'eth0.1'
    option force_link '1'
    option type 'bridge'
    option proto 'static'
    option ipaddr '192.168.1.1'
    option netmask '255.255.255.0'
    option ip6assign '60'

config interface 'wan'
    option ifname 'eth0.2'
    option proto 'dhcp'
    option broadcast '1'

config interface 'wan6'
    option ifname '@wan'
    option proto 'dhcpv6'

config switch
    option name 'switch0'
    option reset '1'
    option enable_vlan '1'

config switch_vlan
    option device 'switch0'
    option vlan '1'
    option ports '0t 2 3 4 5'

config switch_vlan
    option device 'switch0'
    option vlan '2'
    option ports '0t 1'

See http://wiki.openwrt.org/doc/uci/network

"Enable the broadcast flag in DHCP requests, required for certain ISPs, e.g. Charter with DOCSIS 3"

I'm not sure if your ISP would need this active, but it's worth a try as a first step in troubleshooting. Yes, you have it in the correct spot.

(Last edited by kgoerbig on 25 Jun 2015, 17:15)

With broadcast enabled the connection to the Internet works now without restart for over three days (which is kind of a success, but doesn't mean anything).
As I remember I've also disabled IPv6 once because I had some trouble in this with my ISP as well, but I think I enabled it again some time later to give it a try again. Now I have loading problems for some pages, while it works for other pages. My guess is, it is also related to IPv6, since ping works for heise.de, openwrt.org and google.com, while ping6 can resolve the name but doesn't seam to be able to send and receive pings.
So how do I disable IPv6 in a way that I can easily enable it again once my ISP gets it all setup correctly?

Have you made any changes to the default IPv6 configuration? If not, then it should not be an issue. The only way for your problems to be related to ipv6 is if you have semi/non-working ipv6 configuration on your PC.

The ipv6 resolvability is not an indication, since ipv4 DNS would return AAAA records for the given zone.

You are better off debugging the pages in question, i.e., see if your browser is connecting via ipv6 or ipv4.

In any case, paste the result from 'ifstatus lan' and 'ifstatus wan6'

On the disabling of IPv6. There many ways to disable ipv6. But perhaps the easiest is to put 'net.ipv6.conf.all.disable_ipv6=1' in '/etc/sysctl.conf'. Then execute 'sysctl -p /etc/sysctl.conf'. And then it should dynamically clear all ipv6 addresses from all interfaces, but in case it does not, then execute '/etc/init.d/network restart' or 'reboot'. I should warn you that there are services (daemons) which won't be able to operate that way if you don't make the respective configuration changes and disable their ipv6 support, i.e., listening on ipv6.

An even easier way for you to switch off some of the ipv6 functionality might be to disable ipv6 forwarding by changing "net.ipv6.conf.default.forwarding" and "net.ipv6.conf.all.forwarding" to 0 /That will disable RA and SLAAC/. You can find these two in /etc/sysctl.conf and don't forget to rerun 'sysctl -p /etc/sysctl.conf'. Then also disable the dhcp ipv6 support by commenting out the "option dhcpv6 'server'", "option ra 'server'" and "option ra_management '1'" in /etc/config/dhcp by prepending each line with '#' character. The run '/etc/init.d/dnsmasq restart' or better reboot.

Thank you @minix for this explanation. I've just disabled/stoped the "wan6" interface by clicking "stop" next to "WAN6" in the "Interface Overview" and immediately the pages started loading correctly. I guess this setting will not remain after a reboot and I think I have to set "option enabled '0'" in wan6 in /etc/config/network.

Regarding the broadcast, I still don't understand, why it worked all the months before without enabling broadcast, but it seams to be fine for now.