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Supernetting an existing network

Posted on 2011-03-07
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Last Modified: 2012-05-11
Hi,

I have a network 192.168.1.0 /25.  This network's use has ballooned and I only have 4 addresses left to give out.  I would like to change it to 192.168.1.0 /23 (to go from 126 addresses to 510).  Here are my steps :

1. Change the firewall interfaces for 192.168.1.0 to the new subnet (as the firewall also does the routing between networks).
2. Change the servers subnet masks from /25 to /23 as time permits (during this time all /25 hosts should be able to communicate without issue correct ?  They will have to change to /23 subnet inorder to communicate with new nodes in the new parts of this subnet correct ?).
3. I do not run any routing protocols like RIP or OSPF (everything is static), so no biggie there.

Am I oversimplifying things ?  Is there anything I am missing ?

Thanks
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Question by:Elemental12
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4 Comments
 
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by:macoronat
macoronat earned 167 total points
ID: 35057245
Everything sounds fine.  Just remember that you will need to keep the same default gateway address in order for the devices that are already working in your network, to keep on communicating with the outside and not just between devices within the same network.
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by:Ernie Beek
Ernie Beek earned 166 total points
ID: 35057398
Only keep in mind that when changing to the new subnet, the network will become 192.168.0.0/23 (and not 192.168.1.0/23 as you put it). So the range will be: 192.168.0.0-192.168.1.255
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Jan Springer earned 167 total points
ID: 35057403
The only problem that you might run into is if any of your equipment expects the subnet with mask to fall on a CIDR boundary, i.e., you might have to use 192.168.0.0/23.
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Expert Comment

by:pwindell
ID: 35062282
No everything is not fine.  Ethernet should not have subnets beyond 250-300 Hosts.  Rolling back the mask by just one bit jumps it to 510,...then next bit jumps to 1022.  Someone my argue that 350-400 won't hurt performance but 510 is too much.

For every 200 Hosts create a new subnet.  All it takes is the addition of a simple LAN Router.  If a company can afford to have a network larger than 200 machines then there is no way they can argue that they can not afford a simple LAN Router.
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