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TCP/IP Addressing Scheme

By whiddeng ·
Recently, we have increased the number of ip addresses needed to over 240, so we decided to go to a class "B" network. We used the "172.23.16.0" with subnet mask of "255.255.240.0". We used a different subnet for different locations. Location "A"172.23.16.1-254, location "B" 172.23.17.1-254, etc. The PDC is on 172.23.16 subnet, the problem is all the others have inconsistent problems seeing each other. I have setup a "WINS" and "DNS" server to try and eliminate problem, but I cannont seeany difference. Is there something wrong with my subnetting or something that I have missed?

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TCP/IP Addressing Scheme

by ckilday In reply to TCP/IP Addressing Scheme

What address space were you using before you decided to make the switch to class B? If your intent was to move to a private class B space, you should use something in the 172.16.0.0 range. 172.23.0.0 would be a public class B and therefore allowedto travel across the internet. If you are not performing NAT at your internet interface, it's possible you are finding routes to another network and either timing out or being rejected by another network. You could try performing traceroutes between networks and see where you end up. Best wishes.
- ck

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TCP/IP Addressing Scheme

by whiddeng In reply to TCP/IP Addressing Scheme

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TCP/IP Addressing Scheme

by eBob In reply to TCP/IP Addressing Scheme

It looks more like you're using a subnet mask of 255.255.255.0. This lets you identify "172.23.16.0", with address range "172.23.16.1" through "172.23.16.254" as one sub-network, and "172.23.17.0", with address range "172.23.17.1" through "172.23.17.254", etc. Just go and redefine the mask on your PCs and routers and see if that fixes things.

You may need to provide some sort of "helpers" for systems not on 172.23.16.0 to see the PDC, even after fixing your subnet masks. Check with simple PINGs, and also by trying to login to your domain. If you do need "helpers" the simplest to use (but most difficult to maintain) are of course LMHOST files.

As for whether 172.23 is "public" or "private": it is in the "private" range, so you're OK. For further info on this, see the RFC at:

http://www.isi.edu/in-notes/rfc1918.txt

where it says (among other things):

172.16.0.0 - 172.31.255.255 (172.16/12 prefix)

are part of the IANA "Private" address space.

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TCP/IP Addressing Scheme

by whiddeng In reply to TCP/IP Addressing Scheme

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TCP/IP Addressing Scheme

by isys In reply to TCP/IP Addressing Scheme

Verify your routing tables. WINS and DNS will not help if your routers don't know where to send the packets.

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TCP/IP Addressing Scheme

by whiddeng In reply to TCP/IP Addressing Scheme

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TCP/IP Addressing Scheme

by curlergirl In reply to TCP/IP Addressing Scheme

If you are actually using the subnet mask 255.255.255.240, then the IP addresses 172.23.16.1-254 would not all be on the same subnet, nor would 172.23.17.1-254. So not all of the computers within those ranges of addresses would be able to reach others within the same range without a router. To use the IP addressing scheme you describe so that 172.23.16.x comprises only one subnet and 172.23.17.x comprises only one other subnet, you need to use the subnet mask 255.255.255.0. This is independent of WINS and DNS, which are methods of resolving IP addresses to NetBIOS names so that computers can reach each other by name rather than IP address. Hope this helps!

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TCP/IP Addressing Scheme

by whiddeng In reply to TCP/IP Addressing Scheme

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TCP/IP Addressing Scheme

by isys In reply to TCP/IP Addressing Scheme

Using netmask 255.255.240.0 you have one subnet running from 172.23.16.1 through 172.23.31.254, or 4096 hosts. If you want different sites to be on different subnets you will have to close the mask to 255.255.255.0. If you are treating the different sites as individual subnets your routers can't find the correct routes.

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