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Subnetting Help

Posted on 2013-11-13
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Last Modified: 2013-11-13
HELP!!!

I have been given an assignment to perform subnetting and although I know the very basics, this has me working like a monkey doing a math problem.  I am beyond lost.

The assignment states:

Develop an IPv4 addressing scheme for a remote office using the address 172.36.0.0/23 with a minimum of IP waste for PC networks and exactly the correct number of IP's required between routers.  Also to provide a list of available (unused) nets by using the least number of bits for the subnetmask - CIDR.

Router One:
     Finance = 11PCs
     Account Room = 228 PCs
Router Two:
      IT Office = 5 PCs
     Web Sales = 58 PCs
Router Three:
     Administration = 5 PCs
     Business Section = 112 PCs

I have to provide the following for each (finance, IT Office,Administration, Business Section, Account Room, Web Sales) :
     Subnetmask being used
     NET ID
     IPs required
     IPs calculated
     First available host address
     Last available host address

Connections between the firewall router and router :
    subnetmask used?
     NET ID used?
     IP address assigned to firewall connection?
     IP address assigned to router 1 on firewall side?

Connections between router 1 & router 2
     subnetmask?
     NET ID?
     IP of router 1?
     IP of router 2?

Connections between router 2 & router 3:
     subnetmask?
     NET ID?
     IP of router 2?
     IP of router 3?
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Question by:tmartin40
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Accepted Solution

by:
Henk van Achterberg earned 2000 total points
ID: 39646087
Ok, the smallest subnet between routers is 255.255.255.252 (four IP's, first IP is NETWORK address, last IP is broadcast address).

so we start with the firewall and routers:

172.36.0.0/30 <- NETID
172.36.0.1 - firewall
172.36.0.2 - router 1

172.36.0.4/30 <- NETID
172.36.0.6 - router 1
172.36.0.7 - router 2

172.36.0.8/30 <- NETID
172.36.0.9 - router 2
172.36.0.10 - router 3

Then you need the subnets for the routers:

Router One:
     Finance = 11PCs 172.36.0.32/28
     Account Room = 228 PCs 172.36.1.0/24
Router Two:
      IT Office = 5 PCs 172.36.0.16/29
     Web Sales = 58 PCs 172.36.0.64/26
Router Three:
     Administration = 5 PCs 172.36.0.24/29
     Business Section = 112 PCs 172.36.0.128/25

so that have we used:

172.36.0.0/30
172.36.0.4/30
172.36.0.8/30
172.36.0.12/30 [UNUSED]
172.36.0.16/29
172.36.0.24/29
172.36.0.32/28
172.36.0.48/28 [UNUSED]
172.36.0.64/26
172.36.0.128/25
172.36.1.0/24

Here ya go
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Author Comment

by:tmartin40
ID: 39646123
OK, let me show my ignorance...

The subnetmask for the firewall and all routers is 255.255.255.252 and 172.36.0.0/30 is the netID for the firewall/router 1.  The "/30" is confusing to me.  This confusion carries over to the departements.  For example:

Finance = 172.36.0.32/28... This translates to a host IP range of 172.36.0.33-172.36.0.46 with a net id of 172.36.0.32, a broadcast ID of 172.36.0.47, and a subnet mask of 255.255.255.240?
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LVL 12

Expert Comment

by:Henk van Achterberg
ID: 39646143
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Author Comment

by:tmartin40
ID: 39646146
Got it, THANKS!!!  You are a life saver!
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