subnetmask

jkbarik

Junior Member
Apr 30, 2016
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0
0
Hello friends
my router is connected to internet (ISP) in the up stream. In the down stream it it connected to a switch-A. Then switch-A is connected to three switches-B-C-D. Each switch is (B/C/D) is connected to 8 computers. If the local IP address of my router is 192.168.0.1 then how do I select the subnet mask for each sub network(B-C-D)? I want to set manually not dynamic allocation. How do I select IP address for each computer?

thanks
 

retsam

Junior Member
Aug 2, 2011
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0
66
if you need three separate networks than you need a routing protocol setup like RIP or OSPF. Than you need to tell your router the three networks.
Network A 192.168.0.0 subnet mask 255.255.255.0 default gateway 192.168.0.1 address ranges used for hosts 192.168.0.2 to 192.168.0.254

Network B 192.168.1.0 subnet mask 255.255.255.0 default gateway 192.168.1.1 address ranges used for hosts 192.168.1.2 to 192.168.1.254
Network C 192.168.2.0 subnet mask 255.255.255.0 default gateway 192.168.2.1
address ranges used for hosts 192.168.2.2 to 192.168.2.254
I'm assuming you need three separate networks? is this correct
 

frowertr

Golden Member
Apr 17, 2010
1,372
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There really should be a homework forum where we could help people at instead of cluttering up the real Networking forum.
 

Pandasaurus

Member
Aug 19, 2012
196
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I'm still just trying to figure out how retsam has been a member since 2011, and just made their first post today...
 

Gryz

Golden Member
Aug 28, 2010
1,551
204
106
I'm still just trying to figure out how retsam has been a member since 2011, and just made their first post today...
I believe you can't do searches in forums, unless you are a member. That would be a reason to join and not post at first.
 

Gryz

Golden Member
Aug 28, 2010
1,551
204
106
As usual here, people have ideas about routing that are not (completely) correct. So I'll respond. But jkbarik, do your own homework. Or tell us next time you have a homework question that you can't answer.

if you need three separate networks than you need a routing protocol setup like RIP or OSPF.
No.

You need a routing protocol when you have multiple separate networks, that are not directly connected. In other words: when the hopcount between two of those networks is larger than 1. In other words: when you have more than 1 router in your network.

And even then, you can design/configure all those networks with static routes, in stead of a routing protocol. Only when you have redundancy in your network, then you need a routing protocol. In other words: when you have more than 1 path between router A and router B.

Than you need to tell your router the three networks.
I don't think so.

Notice the description of the question.
Router is connected to switch-A. Switch-A is connected to switches B, C and D. A switch means a bridge. Most of the time. (The word "switch" sucks in networking. It can use many things. Better wording would be: "bridge").

So from a routing perspective, a layer-3 perspective, it is one big ethernet.

Network A 192.168.0.0 subnet mask 255.255.255.0 default gateway 192.168.0.1 address ranges used for hosts 192.168.0.2 to 192.168.0.254

Network B 192.168.1.0 subnet mask 255.255.255.0 default gateway 192.168.1.1 address ranges used for hosts 192.168.1.2 to 192.168.1.254
Network C 192.168.2.0 subnet mask 255.255.255.0 default gateway 192.168.2.1
address ranges used for hosts 192.168.2.2 to 192.168.2.254
That's correct, if we were talking about multiple networks. And even then, because there are 4 switches, if we did 1 subnet per switch, we should need 4 networks.

I'm assuming you need three separate networks? is this correct
That's what jkbarik should tell us. But I doubt he can, because it seems he doesn't even understand the question.

Also there is the issue: do you need to assign a subnet mask that just works ? Or a subnet-mask that works, but is also as long as possible. A /24 (as you use) has 256-2=254 ip-addresses available for hosts (and routers). Here we need 8 ip-addresses for hosts, and 1 or 2 for routers.So we need a subnet that has 10 ip-addresses. That means we need a /28. With 28 bits subnet mask we have 2^4 = 16 - 2 = 14 available ip-addresses.

But these are 4 switches, then this is one subnet. The easiest thing would be to just assign 192.168.0.1/24 (24 = length of the netmask in bits) to the one subnet. And give the 24 (24 = 3 * 8) hosts an IP-address from that range. Say 192.168.0.101 till 192.168.0.124.


Edit: oh, for the uninitiated:
a /24 means a netmask which is a bitstring of 24 ones and 8 zeros. 11111111111111111111111100000000.
a /28 means a netmask which is a bitstring of 28 ones and 4 zeros. 11111111111111111111111111110000.
If you write that as separate bytes, you'll end up with all ones in the first 3 times 8 bits.
11111111 in binary is 255 in decimal.
00000000 in binary is 0 in decimal.
11110000 in binary is 240 in decimal.
So a /24 will be written in dotted-4-octet-notation as: 255.255.255.0
And a /28 will be written in dotted-4-octet-notation as 255.255.255.240.
 
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