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2 different subnets visible to explorer

Posted on 1997-08-04
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Last Modified: 2013-12-23
I actually got this to work. I don't want to/didn't use WINS. The goal is to have subnet 192.168.145.# and subnet 192.168.126.# visible to each other. (192.168 was used to protect the innocent :) , but 145 and 126 are accurate) what I did was set my subnet mask to 255.255.0.0 and add each router of each subnet into my list of gateways. My computer is on subnet 192.168.145. This is crude, but I was able to map a drive of a computer on the 192.168.126 subnet. I had to know what it was shared as for this to work. Now, the problem is that I cannot see about 85% of my subnet in Network Neighborhood. Is there a way of cleaning up the subnet mask to only see 192.168.145 and 192.168.126? hence having both full subnets visible in Network Neighborhood? This was very exiciting just to
see actually work. I can get this to work on WinNT 4.0 Workstation as well.
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Question by:dmcgarry
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Philippe earned 200 total points
ID: 1548008

garry,

You should not have IP connectivity to the other subnet with such a netmask. The netmask says that if the two first bytes are identical to the ones of your host then the other host must be on the same subnet. This means that your host will not try to go through a gateway to reach the machines on the other subnet.

To test IP connectivity you can simply run a ping on your host:

ping 192.168.126.other_machine

With your setup, this should timeout.

My guess is that your router is not a pure IP router and it that it forwards netbui broadcasts.

To answer your question about netmasks, no, it is not possible to set the mask to only match these two subnets. Your netmask matches all subnets that start with 192.168. It turns out that in your example, the two first bits of the third bytes are identical (10), thus you could use a netmask of 255.255.192.0 which would match all networks that have the same first two bytes and the same first two bits of the thid byte (that would be 64 different subnets). If you wanted to select only two subnets, their third byte should have the same first seven bits. Eg: subnets 192.168.145. and 192.168.144 with netmask 255.255.254.0. This mask would only match the two subnets.

cheers,

  Philippe

If you think this doesn't answer your question you can post a comment to ask for details before rejecting the answer.

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by:dmcgarry
ID: 1548009
Ok. I do understand what you said about the subnet masks. Thats perfectly reasonable. However, I can guarantee you that I have a pure router on both subnets. each subnet has it's own router, that has fiberoptic going to a central location. This is at a company that deals heavily with internet conectivity and software. We have T3's coming out of this building to the/an internet backbone as well as between other parts of the company. I do not believe that your ip test times out. I can go out on the internet, do anything as if the subnet mask was 255.255.255.0. The only drawback is my Network Neighbor hood is 85% empty, possibly do to defining 64k computers as my subnet?
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by:Philippe
ID: 1548010

Garry,

The netmask is used by your machine (say A) to know if another machine (say B) is on the same subnet or not. The netmask tells which bits of the addresses must be indentical for the two machines to be in the same subnet.

Whenever your machines sends a datagram it uses the netmask to check whether the destination is on its subnet. If it is, it sends it directly to the destination address. If it is not, then it sends the datagram to a gateway, which will then forward it in the direction of the destination.

If your netmask is supposed to be 255.255.255.0 it means that all machines on your subnet have the same first three bytes (192.168.145). If you set it to 255.255.0.0 then your machine will believe that all machines with (192.168) are on the same subnet. You should have no problem reaching any host in the internet which does not start with 192.168. However, you should not be able to reach a machine with address, say, 192.168.99.99. Your machine will believe that it is on the same subnet and thus not send it to a gateway and it will not be forwarded out of your subnet.

So much about netmasks, ain't that fun?

Note that you don't need IP to see other machines in your windows explorer. By default windows tries to use the netbeui protocol rather than IP when possible. My guess is that the router between the networks also forwards netbeui packets. You could test that either by doing the ping test and see if it times out or by removing the netbeui protocol (only if you know how to reinstall it!) and check if you can still see the machines on the other subnet.

Now, it could be that your routers are configured in a special way such that your packets still get forwarded. In that case I would guess that the 80% of hosts you can see are the ones that are listed in your lmhosts file. Check in your windows directory (or is it the system directory? better do a search) to find if you have a file called lmhosts. When you don't use WINS, windows uses the lmhosts file to look up IP addersses of lanmanager names.

 hope this helps,

    Philippe

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Author Comment

by:dmcgarry
ID: 1548011
In the middle of setting up your protocol test suite :-) I do not have a file named lmhosts. This is not a pre-setup machine. Everybody in the building is responsible for setting up their own machines, which isn't a big deal - we all have a "general " knowledge of win95 networking. We wipe them clean periodically to come back to an existing backup that does not have any pre-existing files or registry entries from our product in development. When we first get our machines, we usually just fdisk them immediately for peace of mind knowing we are the only person who put files on the disk.  I'll get back to you after I try the test suite.

I also have to routers that are on subnets 60 and 61. Can I use a subnet mask of 255.255.254.0 to group these? (00111100 = 60 and 00111101 = 61 so  11111110 = 254 are the common bits?)
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by:Philippe
ID: 1548012


> I also have to routers that are on subnets 60 and 61. Can I use
> a subnet mask of 255.255.254.0 to group these? (00111100 = 60
> and 00111101 = 61 so 11111110 = 254 are the common bits?)

Kind of. Setting the mask to 255.255.254.0 will make your machine believe that 60 and 61 form one subnet. The machine will know that anything that is not 192.168.60 or 192.168.60 is not part of the subnet. However, as I said, with this mask a machine on 60 will try to send datagrams to a machine on 61 without going through a router.

Wonder what your test results will be.

  Philippe

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Author Comment

by:dmcgarry
ID: 1548013
Ok. First off, I don't have/never had netbeui installed on my machine. I don't have an lmhosts file. With the subnet mask set to 255.255.0.0 I can ping a machine on a different router/subnet. As a matter of fact, I am writing this comment with the subnet mask at 255.255.0.0 w/out netbeui. The only thing left is that I have magic routers?
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by:Philippe
ID: 1548014

No, no magic here. Here is my guess:

Your company has probably been allocated a classe B address with the first two bytes being 192.168.

They have divided it into smaller subnets differenciated by the third byte (eg 192.168.60 and 192.168.61).

The routers also act as bridges, thus traffic within the 192.168 addresses needs not be routed.

That is only my guess. The best thing would be to ask the person who set up the network!

Now, concerning the netmasks, I think I told you all about it. Could you please grade my answer? We can still discuss your network via comments after that.

  cheers,

     Philippe



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Author Comment

by:dmcgarry
ID: 1548015
Thanks for your help. You did answer my questions about subnet masks, and now I know what my router situation is. I'd buy that last comment that we own a Class B net 128.127.#.#; i've been reading a little bit in the midst of the comment.
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by:dmcgarry
ID: 1548016
oops. I didn't mean to say the ip #. any way of taking out that comment?
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by:Philippe
ID: 1548017

garry,

thanks for the grade.

>  any way of taking out that comment?

Only way is to send e-mail to experts-exchange, eg. problems@experts-exchange.com

 cheers,

    Philippe

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