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Challenge for networky types: Multi IPs, one W2K box, conflicts...

Using multiple non homogenous IPs on one W2K/IIS5 box

     
7:26 pm on Feb 28, 2005 (gmt 0)

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Hi folks.

I've a W2K/AS server which currently lives on an IP. Let's say for the sake of argument it's:

a.b.c.d with a subnet of 255.255.255.248 (i.e. /29)

I have another IP, on a completely different subnet, to point to the server, e.g.:

w.x.y.z with a subnet of 255.255.255.252 (i.e. /30)

The firewall has been opened to allow either IP on port 80. I've a new website that for various reasons has to live on this new IP, whilst the other websites live on the original IP. IIS5 allows for this, and I've set it up accordingly. Both IPs correspond to one network card in the server, and have been setup properly as far as I can tell.

The problem is that though the second IP pings, the site (whose DNS is setup properly) does not respond. In the event logs, I see the following message:

The system detected an address conflict for IP address w.x.y.z with the system having network hardware address 00:05:85:ss:ss:ss. The local interface has been disabled.

IPConfig /all confirms this, as the new IP is reset to 0.0.0.0 with a subnet of 0.0.0.0. Incidentally, in the example above I obscured the last part of the MAC address.

What I know for a fact:
(1) ISP reckons everything configured properly on their part;
(2) No such network hardware having that MAC address exists in my server;
(3) Something ain't right :-)

FYI, without giving too much away, the original (working) IP is of the form 212.20.xx.xx address, and the new one is of the form 84.19.yy.yy. The machine routes via a gateway on the 212.20.xx.xx ISPs network.

Any ideas? Or am I fighting a losing battle against the black art of IP routing?

Ta,

John

7:40 pm on Feb 28, 2005 (gmt 0)

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Oh, before I forget. The message that browsers get back when they try to surf to the site on the new IP is:

"The connection was refused when trying to contact www.thedomaininquestion.com."

(obviously that's not the real domain but rules are rules...)

John

8:29 pm on Feb 28, 2005 (gmt 0)

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Hmm - most likely, there *is" a machine somewhere on the network that thinks it has the same IP as your server.

As a side note, although IIS supports multiple IPs, generally Windows only supports one default gateway. This could create issue if either the routers upstream on those two links cases about source routing, you might find packets get dropped. I don't think that's what's going on at the moment, but something to watch out for.

Good luck finding the device with the conflicting IP.

2:29 am on Mar 1, 2005 (gmt 0)

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unbind the address.

run ipconfig to confirm it is unbound.

ping the address to prove to yourself it does still exist somewhere out there.

find the offending machine.

whack someone upside the head.

having multiple gateways on non-contiguous nets is not a problem as long as the subnets are configured properly.

9:12 am on Mar 1, 2005 (gmt 0)

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Thanks, have tried this - adaptor unbound from the iffy IP, and yet it still pings.

Running tracert on the IP is interesting - it must be very close by as it gets there in one hop, but to be fair I'm not a networking-minded fellow and I get a bit lost.

Would you say that if it tracert's in one hop, it is likely to be something setup in the routing between the ISP and my co-hosted box? Or is the one hop more likely to be due to the adaptor not being unbound (though ipconfig /all reveals no sign of it).

I'm confused :-(

John

11:15 am on Mar 1, 2005 (gmt 0)

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Got it working: was a case of bad communication between ISP and myself. The IP I thought I had was not the IP I was allocated - but once I tried the IP that they thought that I had been trying, it 'just worked' (Mac styley ;-)

Happy John

 

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