Clarification please on Subnetting-ip subnet-zero

itdaddy

Hello dudes

this is what I have seen.

Subnets = 2^n - 2
Hosts = 2^n - 2

ip subnet-zero /applied global config mode

''
Subnets = 2^n /changes it to this so all 0s and all 1s can be used as ip addresses
Hosts = 2^n - 2

is this correct?

Thanks

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Comments

mitchellislearning

when u r using ip-subnet-zero idt u have to subtract two. i may be wrong tho

itdaddy

mitchellislearning

no I am 90 % sure that with the ip subnet-zero it allows you to use the all 1s and all 0s
that is why it came to be; I am just making sure that it is correct what i have.
but thanks

nicklauscombs

itdaddy,
you are correct in your thinking, on a side note newer IOS has this on by default

mitchellislearning

well now im curious. im a n00b, i just finished subnetting in my book and would like to know. was i even close to right or do i need to read it all again

dynamik

You're right.

Also, you'll have to subtract 2 if you're using classful routing protocols, like RIPv1 and IGRP*

*At least I think that's right. Are there any other scenarios when you'd still have to subtract 2?

Plazma

heh yea, ip-subnet-zero is so common now that it makes you think it was ever an "option" back in the day.

itdaddy

mitchellislearning

re read man! it takes a bit and the go to the site. subnettingquestions.com
nice site that drills your skills and i do believe they use ip subnet-zero

dynamik: good point in a classful really? I thoughi ip subnet zero was for all classful and classless?

can you point me to some documentation on your statement dynamik
not to sound distrustful but want to see documentation on this statement about with classful
it need the -2. thanks buds!
robert

Slowhand

itdaddy wrote:

Hello dudes

this is what I have seen.

Subnets = 2^n - 2
Hosts = 2^n - 2

ip subnet-zero /applied global config mode
''
Subnets = 2^n /changes it to this so all 0s and all 1s can be used as ip addresses
Hosts = 2^n - 2

is this correct?

Thanks

Looks good to me. Unless I'm completely out of it today, that is exactly what I learned during my CCNA studies. You don't need to subract two when subnet zero is enabled, (which is default these days on most Cisco devices). For the hosts, though, you've always got to subtract two from your total count, since the broadcast and network addresses can't be used as hosts.

itdaddy

nicklauscombs

thanks for your reply i appreciate all yu dudes; we can do it together

pass these certs!

hackers work in groups why cant we!

nicklauscombs

it daddy - when is your exam scheduled for?

dynamik

Actually, I think I'm wrong. I think you can't subnet at all when using classful routing protocols.

I'm studying for all three of these exams at once, and my brain is just turning to mush

itdaddy

nicklauscombs

7 aug 08 if i dont pass I can take the 2nd shot which i will i have till oct to take 2nd shot
and i will take it; i ask the testing place and pearson vue and they said i have 2nd shot
coming since my first exam I took ccna 801 locked up on my half way, I got a free voucher to take 802 exam and they said I an get a 2nd shot on 802.

but yeah, i am taking the following week off before exam to make sure i over study.
i have poor short term memory. okay plus take a little vaction that week but mostly study
my brains out; i have to study right up to exam. I can see that i am improving on my
Bryant Exams hitting aroun 80s on all my exams good and subnetting in he 90s percentile
i feel good...thanks

Dynamik i do understand doing too many things and information getting crossed
working on my BS degree in Computer Science while stuyding ccna and of course work related issues in Microsoft/Unix. gets to be nutz; I wish i had lots of time like some guys who teach
who have like 20 weeks to study only ;that would be cool but such is life..I hope to be ccnp and maybe ccna voice in 2-3 years seems feasible Microsoft track i would like to be MCSE 2k3 at least but then I might have to shave my head and go to the remote island of microsoft. that would be cool and have my work pay for my career hahhahah

wish me luck!
my blog i have been using for studying so i have clean notes; will look over my blog notes prior to exam. i feel i have many things cover just need to make it solid and work on memory drills

but I am excited! getting; was scared but now excited since i can feel it come together (just need to work on my typing and spelling ahahaahahh )

Slowhand

dynamik wrote:

Actually, I think I'm wrong. I think you can't subnet at all when using classful routing protocols.

I'm studying for all three of these exams at once, and my brain is just turning to mush

That's how they getcha. And you're correct, there is no subnetting involved with classful routing protocols. Subnetting didn't come into play until VLSM was supported by things like OSPF, EIRGP, and RIPv2. It's funny how things begin to leak out of your brain when you're not completely absorbed in them anymore. I find myself trying to remember things now, that were second-nature during my CCNA studies.

nicklauscombs

itdaddy wrote:

7 aug 08

just remember to go into the test center like this

and rip the exam a new one

itdaddy

nicklauscombs

I like that. It has been getting like that recently. Looking and do things over and over till I am just sick; I am taking Aerogon's point of view. and overstudying till I puke. 1.5 minutes per question sucks; either you know it or don't. yikes. Hey this is stupid but check this out.

if in ip subnet-zero you do this 2^n=subnets
then why dont we do this hosts = 2^n??? I mean when we use ip subnet-zero enable mode
why not do the 2^n for both hosts and subnets?? all 1s and all 0s isnt that why we do it? so wouldnt it go for subnets and hosts.now i am confusing myself. when I do my problems it seems it only is applied to subnets and not hosts..can some one knock me in the head to clarify my confusion. thanks

because isnt the reason we do the 2^n-2 is to take off the first and last host due to no ip subnet-zero enabled???