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Devices connected via ethernet cable losing connection

  • shaneoh1980
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03 Nov 2016 09:56 #87154 by shaneoh1980
Replied by shaneoh1980 on topic Re: Devices connected via ethernet cable losing connection
Hi Dave,

I've set the second 2860 up and it's ready to swap out if there are more issues. WE seem to have stabilised since I disabled LAN2. Fine for now but we really need that functionality to retain an isolated guest network, so if that ends up being the fix then it's not a good outcome for us.

I'll try the cable fix if I need to troubleshoot again, as well as plugging directly in. The biggest problem is how intermittent the issue is and how inconsistent. It can happen to some users at any given time but not others, and it can sometimes right itself without intervention from me. It makes diagnostics so much harder.

Generally I am able to log into the router when it happens, and I can ping the router, but I cannot ping our tracert to the outside world.

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03 Nov 2016 11:03 #87156 by footsore
Replied by footsore on topic Re: Devices connected via ethernet cable losing connection

shaneoh1980 wrote: Hi Dave,

I've set the second 2860 up and it's ready to swap out if there are more issues. We seem to have stabilised since I disabled LAN2. Fine for now but we really need that functionality to retain an isolated guest network, so if that ends up being the fix then it's not a good outcome for us.

With two 2860s that is easily overcome. First (connected to modem) 2860 is open network with Wifi for guests. Second is plugged into first and operates the secure network. Separate subnets, You can see out but guests can't see in.

Having said that I run 3 LANs on my 2860n with the latest firmware (3.8.4) and all is fine. So you should be able to run two fine.


shaneoh1980 wrote: Generally I am able to log into the router when it happens, and I can ping the router, but I cannot ping our tracert to the outside world.



Are you trying to ping/trace from the router or from the local PC? If the router can't see out it infers a problem with the connection to/through the modem. If it can see out and you can't it infers a DNS or local network problem.

All the best problems are intermittent. And when you finally solve it you won't even know for sure!

Dave

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03 Nov 2016 11:32 #87158 by jedi98
Replied by jedi98 on topic Re: Devices connected via ethernet cable losing connection
To find whether you are having a client side DNS issue: when the problem occurs try pinging one of the google addresses 8.8.8.8 or 8.8.4.4 so you can see whether its the name lookup or the ip connectivity that's gone. If the ping works fine then maybe just the DNS is going astray.

If it's just the name lookup, start at the client, and check the DNS address has not changed, e.g. using "ipconfig/all" on windows, and make sure that it is the address that you think it should be.

I still think you have another DHCP or RADVD on the lan, but I still could be wrong!

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03 Nov 2016 14:44 #87161 by footsore
Replied by footsore on topic Re: Devices connected via ethernet cable losing connection

jedi98 wrote: I still think you have another DHCP or RADVD on the lan, but I still could be wrong!


Agreed it is a likely cause.


Just wanted to clarify if the unsuccessful pings were done from the client (e.g. Command Line) or from the router via the web login. Trying to rule out connection problem to internet vs. a local LAN problem. The language isn't entirely explicit and could be read either way.

As stated it isn't affecting wireless clients so I would presume it is local LAN problem:
- extra DHCP server
- dodgy cable between Draytek and switch
- or a config clash between LAN2 and LAN1

Don't see why it would get worse over a period of time - except for a dodgy cable. If stopping LAN2 'cures' the problem then clearly a config clash with LAN2.

Questions on LAN2
- Is/was this just a VLAN or a separate port based LAN?
- Is the Draytek serving IPs for LAN2.
- Is the Draytek providing WiFi or is there a separate AP providing WiFi? Is it serving DHCP addresses? Possible VLAN misconfig on the WiFi device especially if not a port based LAN.
- Is there any VLAN routing set-up?

Plugging a couple of clients directly into ports on the Draytek and seeing if they have the same problems would rule out/in switch/cable problems. 1-minute job so would seem to make sense as a troubleshooting exercise.

Dave

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03 Nov 2016 19:39 #87163 by jedi98
Replied by jedi98 on topic Re: Devices connected via ethernet cable losing connection

Generally I am able to log into the router when it happens, and I can ping the router, but I cannot ping our tracert to the outside world.


That bit sounds like client's default route could be overwritten. You are probably accessing the router by IP address (guess) so it is unaffected by default route problems or DNS so long as it has a lan address. This is a real jigsaw puzzle of clues. Ok, so where's that missing piece?

Ooooh - another thought - just double check that the client PC does not think it has IPv6 address (other than the fe80: ones which are just there to catch you out).

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  • shaneoh1980
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04 Nov 2016 10:54 #87175 by shaneoh1980
Replied by shaneoh1980 on topic Re: Devices connected via ethernet cable losing connection

footsore wrote:
With two 2860s that is easily overcome. First (connected to modem) 2860 is open network with Wifi for guests. Second is plugged into first and operates the secure network. Separate subnets, You can see out but guests can't see in.


That's a good suggestion, though we like to use the other connection (broadband) as a failover for our fibre so probably best to have it all through one. I'm sure it can be done and there is some reasonably simple explanation here.

footsore wrote:
Are you trying to ping/trace from the router or from the local PC? If the router can't see out it infers a problem with the connection to/through the modem. If it can see out and you can't it infers a DNS or local network problem.


From my local PC when it's not connecting to the internet. Good point - next time I will try to SSH to the router and ping from that.

footsore wrote:
All the best problems are intermittent. And when you finally solve it you won't even know for sure!


Ha, indeed!

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