Sudden problem with 2 routers sharing one modem setup

[nic777]

Hi all,

We have been having this weird problem in our office where our ADSL setup of having some servers and routers share one ADSL modem and connect with different accounts does not all of a sudden work anymore.

It has been working for years like this.

The setup is ADSL line->D-Link Modem->Switch<->2 routers and 2 Linux servers then connect via PPPoE over the network to the modem.

When we just connect one router directly into the modem, it does work

It does not work then when we "share" the modem over the network.


- Has anyone have this problem before?
- Does anyone know what the problem could be i.e. common problems we have may have missed?
- Could there be a conflict somewhere which doesn't allow the PPPoE connection to occur over network?



Full back story:

Wanted to get to the gist of my post fairly quickly but here is the full story leading up the problem above:

- We came to the office with no internet connection at all.
- Looked like Line problem but Telkom technician said line was fine and actually tested it on network
- Turned out he didn't test well as our internet still did not work (we weren't supervising him at time)
- After trying everything we decided to measure the voltage on telephone line. Result: nothing, it was dead.
- Traced cables, the wires had short somewhere, changed it one end and voila, internet worked. Still have no idea what caused this problem in first place.
- Only after some testing we found not all servers and routers were up and thus found out the problem described in first part of post.
- Further to this, Telkom technician did say he had to change a DSLAM part in the exchange.
- My best hunch is thus this cause problems in our line and now line doesn't have enough "power" to broadcast over network? Im in software not engineer so not sure this is even possible
- My other hunch is modem is not 100% and needs to be replaced.

Any other ideas?

Thanks in advance

Nick

 

[bekdik]

Some things to try:

does your adsl line connected at all?

have you tried resetting the adsl modem?

If you plug a pc into the dlink can you connect to internet? Can you log in ti the dlink?

If you plug a pc into a router, while the router is pugged into the dlink, can you connect to internet? Can you log in ti the dlink?

Check that you haven't enabled multiple dhcp servers.

 

[nic777]

Thanks beddik, my responses below:

Some things to try:

does your adsl line connected at all?

Yes, when we connect one router directly to the modem i.e. one cable so modem is not on network, then it does work.

have you tried resetting the adsl modem?


Yes, plus we tested another modem as well. No difference.

If you plug a pc into the dlink can you connect to internet? Can you log in ti the dlink?


Yes, we can access modem and connect to internet.

If you plug a pc into a router, while the router is pugged into the dlink, can you connect to internet? Can you log in ti the dlink?

Yes, we can access router and connect to internet. I must say its quite slow at times to connect, took last time 2-3 minutes of waiting for it to finally connect. Usually its very fast.

Check that you haven't enabled multiple dhcp servers.

One of the first things checked and yup, only one DHCP running

I also tested another switch and it was the same result.

I then tested the modem via a switch and same result as well i.e. no PPPoE connection possible over the switch, even when just one PC and the modem on switch.

You can see why I suspect the line now, especially when on Monday the line was dead with no voltage at all.

 

[KillerB]

have you tried more the one switch when you tested through the switch your switch could also be faulty.

 

[bekdik]

It doesn't sound like a line problem as all the problems are downstream, sounds more like a network problem on your side. Did you try each of the routers?

 

[Amida]

Thanks beddik, my responses below:




I also tested another switch and it was the same result.

I then tested the modem via a switch and same result as well i.e. no PPPoE connection possible over the switch, even when just one PC and the modem on switch.

You can see why I suspect the line now, especially when on Monday the line was dead with no voltage at all.

Plug the pc straight into the modem, run a wireshark trace while make the PPP connection and save the log.

Then put the switch in between the pc and the modem and do the same wireshark trace. Then you compare the 2 and see exactly which side is causing the problem.

If you google pppoe you will find exactly what is the order of pppoe packets that need to be sent for a successful connection.

let me know what the result is.

 

[bekdik]

Thanks beddik, my responses below:

I also tested another switch and it was the same result.

I then tested the modem via a switch and same result as well i.e. no PPPoE connection possible over the switch, even when just one PC and the modem on switch.

You can see why I suspect the line now, especially when on Monday the line was dead with no voltage at all.

In the cases where you could connect, were you doing a pppoe dial up as well?

Why are you using pppoe connections? Why not set your dlink to router mode and then all machines on the network will be able to use internet without pppoe. also your isp will only see one connection so you won't have a problem with too many concurrent connections. It will also be easier to set up a firwall for the whole lan, those pppoe's are opening up each pc to the internet, which isn't good.

What are the router's you refer to?

 

[davemc]

Sounds like somebody added an ADSL modem onto the network somewhere, probably in the form of a router that nobody noticed was also a PPPOE capable device.

Perhaps one of the switches that were down previously.