Subnetting question

AndrewA1981

hey

so I'm starting to get into subnetting, and I think I have this concept correct, I just want to make sure I'm on the right track and understand what I'm doing here

if I have a network of say,

192.168.30.128/25 and I need to find the broadcast address for that network

I can look at the lowest network bit, in this case, 1 and know that I'm working with an increment of 128. then I could take my network bits and multiply by the power of 2 and see that I've got 2 networks to work with.

so I'd have 192.168.30.0(network) through 192.168.30.127(broadcast)

and then 192.168.30.128(network) through 192.168.30.255(broadcast)

so my broadcast for the .128 network would be the .255?

also I have one more question that keeps popping into my head as I'm doing these subnets, do you actually run into public ip addresses subnetting into say 128 hosts and actually used as hosts addresses? In my wan networking experience, which is fairly minimal so I could be totally off base...but wouldn't you just want networks with 2 host addresses, for wan link points? and then you would use private ip addresses for the internal network? I haven't seen this topic covered yet and I've been curious about it

anywho..thanks for any help!

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Comments

chmorin

AndrewA1981 wrote: »

also I have one more question that keeps popping into my head as I'm doing these subnets, do you actually run into public ip addresses subnetting into say 128 hosts and actually used as hosts addresses? In my wan networking experience, which is fairly minimal so I could be totally off base...but wouldn't you just want networks with 2 host addresses, for wan link points? and then you would use private ip addresses for the internal network? I haven't seen this topic covered yet and I've been curious about it

anywho..thanks for any help!

Your logic in subnetting seems to be correct.

In regards to the WAN bit, it is possible to have a point to multi-point WAN link like frame relay so more than 2 hosts could be needed for a WAN. Most of the time though you will find point to point WANs, so 2 hosts would be preferred.

That being said, our network has a fairly large public network space assigned to the midst of some machines. Mostly big copiers that can fax, email, and do a number of other things that (I assume) require a static public IP address for one reason or another.

My point is, just because it does not seem like it should happen does not mean that it won't. You should be prepared for most anything in the real world, and the Cisco world.

SysAdmin4066

Pretty much anything that needs to be accessed externally would need an external IP address (i.e. web servers, VPN routers, etc). Along with the example above, you could need hundreds of different public IP addresses.