UCBNMG: Question for the network wonks

Bill Wyman

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Oct 29, 1997, 3:00:00 AM10/29/97

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The subnet mask below gives you a usable address space of 62 hosts.
It is a little complicated to explain correctly in an email how subnet
masks work. For a clear explanation, I can probably round up some
references; just drop me an email.
Also, you may want to check out the "IP subnet calculator" on Cisco
Systems Inc.'s web page:
http://www.cisco.com/techtools/ip_addr.html
Caren
::::::::::::::::::::::::::::::::::::::
: Caren Litvanyi :
: CU ITS Internetworking Management :
: litv...@spot.colorado.edu :
: voice:303-492-0841 fax:492-4198 :
::::::::::::::::::::::::::::::::::::::

Mark O'Lear

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Oct 29, 1997, 3:00:00 AM10/29/97

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If you convert the subnet mask to binary, you will have
a "mask" of ones that you cannot use in the host ID.
These ones make up the network ID of the address.
Any zeros can be applied to the host ID of the address.

255.255.255.192 is 11111111.11111111.11111111.11000000
in binary, so you can use the last 6 bits for host
IDs with two exceptions. You cannot use a host
ID of all ones (63 in this case) because that is
reserved as the broadcast address. You also cannot
use all zeros as a host ID (this means "any host",
and is used when listening for a connection). This
means that you should be able to use 1-62 as valid
host IDs (which unfortunately in this case is not
the same as the last number in the IP address).

OK, that was the easy part, now for the hard part.
For the sake of simplicity, I am going to treat
the actual network and subnet parts of the network
ID as one in the same (combined). If the first
three numbers in the IP address are the same, you
can have four possibilities for network bits in
the last number of your IP address, 00, 01, 10
and 11 (these are replacing the two ones in the
last number of the binary subnet mask at the top).

Your IP range will be as follows:

Net Bits First Valid IP Address Last Valid IP Address
-------- ---------------------- ---------------------
00 XXX.XXX.XXX.1 XXX.XXX.XXX.62
01 XXX.XXX.XXX.65 XXX.XXX.XXX.126
10 XXX.XXX.XXX.129 XXX.XXX.XXX.190
11 XXX.XXX.XXX.193 XXX.XXX.XXX.254

Mark

Bill Wyman

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Oct 29, 1997, 3:00:00 AM10/29/97

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Hello all,

One of my client sites is running low on IP addresses, and I'm trying to
figure out how many they have total. I know the TCP/IP subnet determines
this, but I don't know how to translate it. The subnet is 255.255.255.192.
Can anyone tell me how to translate this into a range of IP addresses?

Thanks in advance,

Juan Thompson
----------------------------------------------------------------------------
--------
"J. Fitzgerald Thompson - At your service"

Juan F. Thompson
Information Services, CU Foundation
phone: 492 9202 fax: 492 9902
thomp...@cufund.colorado.edu

Dan Jones

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Nov 4, 1997, 3:00:00 AM11/4/97

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Frank is correct that Tessa can help you with your IP address needs. In
addition to calling Tessa at 492-0580 you can use our web page to request
or make changes to IP assignments. The URL for our page is:

http://www.colorado.edu/ITS/LANS/

IP address information can be found under the CU-Boulder IP Applications
section. From this same URL you can also order new Ethernet connections
and Ethernet hardware. If you have any questions or comments on our web
page please feel free to call me at 492-6464 or e-mail
Dan....@colorado.edu.