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Subneting????

By Shanghai Sam ·
Please examin the following imaginary senario;
Company X has 2 routers,X1 and X2.
Router X1 is located at the Admin Offices and holds the admin LAN.
Router X2 is located at the Warehouse and holds the designers LAN.
Router X1 and X2 are connected through a serial cable.

The NT IP address is 150.8.0.0 subnet mask 255.255.248.0 (5 bits borrowed from host field)
This allows for 32 Subnets/2048 hosts.

Let's say
150.8.0.1 to 150.8.7.254 for E0 Router X1 (Admin LAN)
150.8.8.1 to 150.8.15.254 for E0 router X2 (Designers LAN)

OK
But this is what I don't understand;
to the router's serial ports I would assign
150.8.16.1 to S0 on router X1. and
150.8.16.2 to S1 on router X2. (connected via Serial)

NOW my question is; what happens to the other 2044 available addresses in subnet 3?
I can't assign them to any other interface because they are different networks.
Does that means that all does addresses get wasted or is there other way to do it without wasting all does addresses?
Please explain!
Thanks.

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Subneting????

by Shanghai Sam In reply to Subneting????

Hi,

Couldn't you allocate say 150.8.7.254 to one router interface and 150.8.15.254 to the other?

That would effectively remove the two topmost addresses out of each of the ranges and leaving the third subnet totally unused.

With your solution above, the adresses aren't really wasted. If you think about where the third subnet lies "physically"... its between the two routers.

There's nothing else on the serial cable so there's no possibility of any of it being used.

If you could add a hub in there (although not possible with your current serial setup) then you could use the extra adresses as they're in the right segment...

Cheers,
Tim.

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Subneting????

by Shanghai Sam In reply to Subneting????

Hi Tim!
well,the solution you offer is not valid because
150.8.7.254 and 150.8.15.254 are different subnets.
You couldn't assign and address from one subnet to one end (DTE) and a different subnet address to the other end (DCE)because they're thesame network or in this case the same subnet.
You must assign addresses in the same subnet,
to both serial interfaces, that is S0 on router X1 and S1 on router X2.
S0 router X1 and S1 router X2 are the same subnet,you can't assign an address fromdifferent subnet!

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Subneting????

by ckilday In reply to Subneting????

Sorry to say, your current addressing scheme wastes the other 2044 addresses. You do need a different network address to get from serial to ethernet. However, if this is a dedicated connection between two sites in your company, I would suggest using some of the reserved address spaces for your serial links. That way you won't waste your other host addresses. You've got the 10.0.0.0, 172.16-31.0.0 and the 192.168.0.0 networks to choose from. If your routers support VLSM, you can take a single class C and support most, if not all, of your serial addressing needs by using a subnet mask of 255.255.255.252. This allows for 4 addresses: network, serial-1, serial-2 and broadcast. Works like a champ for serial links. Best wishes,
- ck

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Subneting????

by mdl3 In reply to Subneting????

hello Mr.ckilday!
I'm sorry but I'm not familiar with the reserved addresses you mention, could you please explain a little.
I did not know there were reserved addresses available.
It sounds very interesting, I'd like to know a little more about it, is there a site you could refer me to concerning that isue?
very good Mr. ckilday!
Thanks!

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