Question from subnettingquestions.com

crazboy84

Question: What is the first valid host on the subnetwork that the node 192.168.141.56/28 belongs to?
Answer: 192.168.141.49


So this is bugging me, my answer is 192.168.141.57, and i cant figure out how im wrong. Did they just goof the answer?

dark3d

networks increment in 16 (/28 is 4 bits) like so:

192.168.141.0/28
192.168.141.16/28
192.168.141.32/28
192.168.141.48/28 <== here is the network your host is in.
192.168.141.64/28

so, 192.168.141.48 is network address, .49-.63 usable ip addresses.

hope I didn't add to your confusion!

crazboy84

Oh not at all i was being stupid and for some reason thinking a /28 is increments of 8... just started back to working on subnetting today after 6 months of lapse, thanks for your help

dark3d

Yes, you can either memorize the cidr chart or just do the binary math with the bitmask.

I have to refresh after just a few months as well. I learned very early to triple check network masks.. I started out my Cisco experience on a pair of 6509s w/ CatOS and any change you made to the config was live and in production. No room for mistakes!

crazboy84

Man i wish i could have hands on experience. I work in helpdesk and general IT but all networking is done by my boss and were pretty small in my office just 1 router 1 switch in the home office 1 router and 3 or 4 switches and im pretty new and hes keeping all the network responibilities which i dont blame him but our networks so simple theres not much to do with it.

dark3d

Yes, I always had the same situation. When you're dealing with a small shop you can't play with the equipment because the business can't function. When you get into large systems then you run into the same issue with change control. They won't let you touch ANYTHING without it being preapproved. Where you will get your experience is duplicating your production environment in a test lab. I had a spare switch on my desk at all times to verify configs before submitting to change control.

jamthat

@ OP, an easy way of finding the increment (same as what dark3d said, but expanding on it a little), is to just subtract 32 from your mask (/28 ) to get 4, then do 2^4 = 16. Memorize your powers of 2 and it's a piece of cake.

More examples:

/27...... 32-27 = 5. 2^5 = 32

/30...... 32-30 = 2. 2^2 = 4

crazboy84

yea i have them memorized, i just goofed when i looked at it from the cobwebs in my head. did 10 questions got 1 wrong, i have subnetting down quite well.

jamthat

crazboy84 wrote: »

yea i have them memorized, i just goofed when i looked at it from the cobwebs in my head. did 10 questions got 1 wrong, i have subnetting down quite well.

Sounds like you're well on your way. Best of luck when test time comes around!