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Subnetting and Default Gateways

post #1 of 6
Thread Starter 
Hi people just a quick one,

Studying for an exam and just reading up subnetting, can you help with the below at all

If I have been assigned a block of addresses from an ISP, for arguments sake its a /16 Address block which connects me to the ISP.

Then I would like to create two subnets within that address space.

ISP provided address block = 137.107.0.0 /16

If I then altered the subnet internally to a /24 address block.

I have already split half of my network addresses on the machines

IE 10 machines on 137.107.1.0 /24 and 10 machines on 137.107.2.0 /24

As these machines are now on a different subnet and are outside of each others broadcast domain, in order to connect to the internet would I have to have two routers configured with the default gateway address for each subnet or can you assign two default gateway address (one for each internal subnet) to the one router?

Thanks guys, any help appreciated as I have melted my brain doing the IP addressing maths and stuff
post #2 of 6
You would need a "router" in each subnet, but they could be virtual interfaces in your physical router like 137.107.1.1 & 137.107.2.1. Either on a router or on a managed switch. At my school they do it with a managed switch which uplinks to the rest of the school, but the switch does DHCP specific to the port the rooms are plugged into.

You could use just one router, but would need to make sure that the ports needed to communicate for internet and almost all communication would need to be open between ports, which is possible, but the easier answer is virtual interfaces in each subnet.
post #3 of 6
Thread Starter 
Thanks for the help feller +1
Much appreciated, makes a little bit more sense now, thats only problem with this book it explains some things and not others
post #4 of 6
Are you required to have the 2 subnets due to the question, or just something you wondered? If you used a larger subnet than a /24 network then less routers or virtual interfaces would be needed.
post #5 of 6
Thread Starter 
hi sorry for the reply did it at work then forgot to check when I got home.

Was just out of the MCTS book so just wondered, it wasnt a question out of it, just didnt quite get it,

Thanks for the help
post #6 of 6
You generally have to have a routing/layer3 device on each subnet.
Routers can have multiple interfaces and subinterfaces (think VLAN).
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