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Old 11-06-2008, 06:43 PM   #1
Registered: Mar 2004
Location: northern michigan usa
Distribution: Debian Squeeze, Whezzy, Jessie
Posts: 882

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Why am I seeing private ip's on a public network

Ladies & Gentlemen,

Thanks for a great site.

Sorry if this is in the wrong form.

I am seeking some help in understanding what I am seeing at my server via etherape. I have a partial understanding, but you know, a better understanding is better.

What I am seeing is on my linux nat/router. On eth1 which is connected to the cable modem I am seeing, in etherape, the ip which is a private ip as I understand it. What I think is happening is that my isp is using that ip for their dhcp server. I never see this ip talk to any other ip except which as I understand it is a broadcast ip.

The ip my nat/router is assigned is not in the private range. I am just not understanding the reasoning behind why they are using this private ip for their server. This ip always seams to use the bootp protocol and never anything else. I do not know what port it is using, have not perused it.

Occasionally I see a different private ip 172.19.41.x I have no idea what this ip is. I am assuming that it is also some kind of server because it only ever talks to the broadcast ip and seams to only use the bootp protocol.

Neither of these two ip ever show up on eth0 which is my local network.

Can anyone give me some help in understanding the reasoning behind this apparent set up?

Old 11-06-2008, 06:53 PM   #2
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I believe cable is actually a shared lan kind of thing for the cluster of users in a nearby area so those private ips your seeing could be from your neighbors.
Old 11-06-2008, 07:54 PM   #3
Registered: Mar 2004
Location: northern michigan usa
Distribution: Debian Squeeze, Whezzy, Jessie
Posts: 882

Original Poster
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Thanks estabroo,

I thought about that and for the 10.x.x.x that does not work because I did a 'ifdown eth1' befor I left for the rest of the day so that the kids could not get online when adults are not home. When I got home I did an 'ifup eth1' and the 10.x.x.x is the ip that assigned me my new ip. If I had a good way to get it off the server to my laptop without typing it in I would post it for all to see (my samba config got all messed up).

As for the other one I would think most home users would use the 192.168.x.x private range and not those for larger networks. I live in a very rural area. The only reason we have cable hear is because there was at one time a small cable company hear around the lake and some years ago it was bought out by one of the big boys. It was even seperate form the cable it town 8 miles away befor it was bought out.

Any other thoughts?


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