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Old 06-12-2008, 01:00 PM   #1
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[part-Linux] ISP Problems with Static IP and MAC addresses

Hello! I've been a frequent visitor of this site, but never really had reason to register before now. I know this problem isn't really Linux related, but since I've only managed to get it to work in Linux, maybe someone knows what goes wrong where. My ISP certainly doesn't seem to know what it's about anyway.

It's a local ISP for the municipiality I'm living in. A common practice here in Sweden is that the local public power company connects their power meters to a grossly over-sized fibre network. They know the potential of selling the bandwidth to the customers of the appartment buildings, so they offer symmetrical 10Mbit or 100Mbit connections to the habitants for cheap money.
This particular one works with static IP addresses, sends you a paper home (which I've conveniently lost) with the necessary information.
The necessary information should be the IP address, subnet mask, standard gateway and two DNS servers, all of which is accounted for. They also use a dodgy login site, which I'm not sure I ever used to get out on the interweb though.

Now I've encountered a problem. Basically I started the connection with a Netgear RP614v3 router, it kept resetting connections, so I replaced the router with a Netgear WGT624v3 which I also had lying around. This one worked splendidly, except that to even get the connection to work, I had to copy the MAC address of the old router to the new one. Generally I thought that the only reason they would bind a MAC address to a unique connection would be for DHCP purposes (which reset after a short period of time 15~40 mins), but since the ISP uses static IPs, I thought it was a little strange. Mainly because I tried unplugging the fibre/cat5 converter for a weekend together with the router, but it still didn't work with another MAC address when I got back.
Now the interesting stuff starts. I bought a new router (A D-Link DIR-635), mainly because the one I'm currently using is a borrow (the Netgear WGT624v3). But I couldn't get it to work even if I configured it like my old router, including stealing the MAC address.
I figured there was something wrong with a setting and went through it all. I've had both the converter and the router unplugged over a night without results.
So, I tried connecting the cable straight into my computer which's dualbooting openSUSE 11 and Windows Vista SP1. In Vista I didn't manage to make it connect, when I pinged the gateway I get:
Pinging 148.***.***.1 with 32 bytes of data:
Reply from 148.***.***.148: Destination host unreachable.
Request timed out.
Reply from 148.***.***.148: Destination host unreachable.
Request timed out.

Ping statistics for 148.***.***.1:
    Packets: Sent = 4, Received = 2, Lost = 2 (50% loss),
the 148.***.***.148 would be my own address. I tried running it a couple of times more, and it altered between a reply and a timeout. Usually it was more timeouts than replies though. I don't really know what the reply thing means as I have to admit I'm adept but not a guru.

So, after another couple of angry phone calls to my ISP where they just said that it wasn't their responsibility to make sure that it worked for me specifically if I at all managed to get it to work (basically, if I managed to get it to work in one situation, it's not their fault).

I decided to try it in Linux. Here I filled out the information again and having no hope at all that it would work I tried it. It actually worked in Linux though! I was shocked.
I tried messing about to see why it worked. Did Linux do something while initiating the connection? It made me try more things in Windows. I tried restarting the windows with the settings already in place, but to no avail.

After getting tired of internet not working, I decided to plug in the old router again. It didn't work anymore! I was shocked again, but I quickly realised that it must be because when I connected with Linux, it did so with another MAC address than the one in the router. I copied the MAC address from my computer to my router and the connection worked again. Now it crossed my mind that it might've worked only because the connection interface the router has resets when you change MAC address, so I asked it to use it's original MAC address for the WAN interface and the connection stopped working again. I changed it back to my computer's MAC address and it started working.

As far as I've come, I feel confident that the error is related to the MAC address somehow. And that Linux did something with the connection that the routers and Windows SHOULD do to make it work, but it also leaves me with many questions.

Why doesn't the D-Link router work when I copy the MAC address from my old router?
Why can't the routers use their own MAC address, but must have an intermediate to initiate the connection?
Did the first router actually establish the connection in the right way or was it just because it was first that made it associate with that IP address? I'd suspect it's the latter in this case though.

After digging around some, I found out about ARP cache. I knew something like it existed, but hadn't really had much reason digging about earlier.
Basically it stores IP - MAC address pairs to save time when sending information and maybe my ISP has configured theirs wrong? Still leaves me wondering what openSUSE did to reset it that no other device managed to do? And why aren't they aware of this problem? Can it only be me?

I might've gotten some technicalities wrong and if so, feel free to correct me.

Last edited by cyberstorm; 06-12-2008 at 01:02 PM. Reason: Missed a word!
Old 06-13-2008, 01:48 AM   #2
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I have to say at first that I don't know what the right solution would be, I just have some ideas that you propably have thought a thousand times.

Anyway, as some Linksys(Cisco) routers are Linux-based and seem to communicate pretty well, I would buy one for 13-day trial and give it a shot.

The other, after trying loads of times the "ipconfig /release" in windows or the linux alternative, I would disconnect the network overnight and then plug in the final device I want the network to work with.

You have propably tried the latter.

Do you have your TCP/IP settings configured to DHCP or Static IP? Tried both with overnight pause?

Allso, I would try to find out more about the web interface of the ISP which you never have used.
Old 06-13-2008, 02:03 AM   #3
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I can think of a number of issues:

1. Once upon a time (I don't currently know of an ISP that does this, btu that doesn't mean they don't still exist) ISPs tried to stop you from allowing your friend to plug in their computer and use your network. So, when you first connected to the service the DHCP server got your MAC and from then on would only talk to that MAC. This (stupid) scheme or else a persistent ARP table are the likely causes of any MAC-related problems. Since you say you actually plugged in your computer (different MAC), they probably don't flush their ARP cache frequently.

2. Some buggy DHCP implementations will not drop a lease unless you explicitly request it. In such a case, the remote equipment might still think that you're connected and refuse to negotiate anything. How do you get your IP number? Is it static but acquired via DHCP, or have you been given a static number, netmask, and gateway and told to just manually enter them?
Old 06-13-2008, 02:05 AM   #4
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It could be that you need your router needs to be "requisitioned" before you can connect to the internet. For a cable system in the US, you browse to the cable box or the ISP's web site, read the terms of service and click on an OK button.

Is the IP address a public or private one?
Old 06-19-2008, 12:04 PM   #5
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I've got a public static address, I got alloted IP, Netmask, Gateway and two DNS servers.
At the moment I'm not at home, so I can't try anything. I've unplugged everything though and hope that keeping them unplugged for 10 days might do a difference. We'll see when I get home! I'm going for the slow ARP cache part.

To clarify:
The Netgear routers worked both. The first one with its own address, but it was the first thing to be plugged in. The second one worked with a copied MAC address from the first router and from my own computer.

The D-Link router does not work even with a copied MAC address.

My own computer worked when I used Linux, but even after getting it to work in Linux it did not work in Windows. I've tried "repairing" the connection and flushing all caches, to no avail.


isp, mac

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