MemberMember Posts: 54 ■■■□□□□□□□
either wendell odom has lost his grapes or i just need a break...either way, i'm pissed because i've hit a wall when everything regarding subnetting was going so well ( although, it has not been the easiest thing to learn )...odom is talking about " drawing vertical lines through rightmost binary 1s/counting up 0s "...i'm fed UP !!...point blank; how does one find the subnet broadcast address when the subnet number and IP are known ?....a simple Boolean AND will not suffice; something tricky has to be done at the end that i can't quite wrap my brain around ( too much coffee today, perhaps ?....i dunno )...odom simply has trouble explaining it....i'd appreciate any help from any CCENTs/CCNAs out there...thanks, guys !....

• Senior Member Member Posts: 556
If you know the subnet number, I'm assuming you also know how to find the range based on the mask? If so, the broadcast address is the last ip in the range, or the address where all the host bits are 1s
• Member Member Posts: 54 ■■■□□□□□□□
pham0329 wrote: »
If you know the subnet number, I'm assuming you also know how to find the range based on the mask? If so, the broadcast address is the last ip in the range, or the address where all the host bits are 1s

maybe i did at one point, but have since forgotten how to do it....thanks, though !
• Network Engineer Member Posts: 150
either wendell odom has lost his grapes or i just need a break...either way, i'm pissed because i've hit a wall when everything regarding subnetting was going so well ( although, it has not been the easiest thing to learn )...odom is talking about " drawing vertical lines through rightmost binary 1s/counting up 0s "...i'm fed UP !!...point blank; how does one find the subnet broadcast address when the subnet number and IP are known ?....a simple Boolean AND will not suffice; something tricky has to be done at the end that i can't quite wrap my brain around ( too much coffee today, perhaps ?....i dunno )...odom simply has trouble explaining it....i'd appreciate any help from any CCENTs/CCNAs out there...thanks, guys !....

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• Senior Member Member Posts: 124
-[7]-[6]-[5]-[4]-[3]-[2]-[1]-[0]-
.128..64..32..16...8....4....2...1........ (2^n = block size) (ex: 2^2 = 4)
/01 /02 /03 /04 /05 /06 /07 /08........(so CIDR /6, /14, /22, and /30 are increments of 4bits)
/09 /10 /11 /12 /13 /14 /15 /16
/17 /18 /19 /20 /21 /22 /23 /24
/25 /26 /27 /28 /29 /30 /31 /32

so if you're in the 3rd octet, and using /30... you are using a blocksize of 4bits.
so you increment by 4.

for example: 192.168.10.0/30 => 192.168.10.0,192.168.10.4, 192.168.10.8, 192.168.10.12
So these are the NETWORK ADDRESSES, and we know the broadcast is the last number BEFORE the next NA.
so the BA for each subnet would be 192.168.10.3, 192.168.10.7, 192.168.10.11, 192.168.10.15.

Lets do another one, in the 3rd octet, maybe a /23 CIDR.

CIDR /23 is 2bits block size, so each sub/network address will be in increments of 2.

172.16.0.0, 172.16.2.0, 172.16.4.0, 172.16.6.0, 172.16.8.0, and so on.
remember these are the network addresses, and the broadcast address is just the last ip address within that network before moving onto the next network.

so the last ip address in the 172.16.0.0 before you get to 172.16.2.0 would be 172.16.1.255.

I cut alot of corners with charts, but if you need it, i can break this down to binary too.
just difficult to explain in a thread/forum.
nerd power.
• Member Member Posts: 54 ■■■□□□□□□□
techie2012 wrote: »

this sounds like what i needed...thanks so much !
• Member Member Posts: 54 ■■■□□□□□□□
xirtlook wrote: »
-[7]-[6]-[5]-[4]-[3]-[2]-[1]-[0]-
.128..64..32..16...8....4....2...1........ (2^n = block size) (ex: 2^2 = 4)
/01 /02 /03 /04 /05 /06 /07 /08........(so CIDR /6, /14, /22, and /30 are increments of 4bits)
/09 /10 /11 /12 /13 /14 /15 /16
/17 /18 /19 /20 /21 /22 /23 /24
/25 /26 /27 /28 /29 /30 /31 /32

so if you're in the 3rd octet, and using /30... you are using a blocksize of 4bits.
so you increment by 4.

for example: 192.168.10.0/30 => 192.168.10.0,192.168.10.4, 192.168.10.8, 192.168.10.12
So these are the NETWORK ADDRESSES, and we know the broadcast is the last number BEFORE the next NA.
so the BA for each subnet would be 192.168.10.3, 192.168.10.7, 192.168.10.11, 192.168.10.15.

Lets do another one, in the 3rd octet, maybe a /23 CIDR.

CIDR /23 is 2bits block size, so each sub/network address will be in increments of 2.

172.16.0.0, 172.16.2.0, 172.16.4.0, 172.16.6.0, 172.16.8.0, and so on.
remember these are the network addresses, and the broadcast address is just the last ip address within that network before moving onto the next network.

so the last ip address in the 172.16.0.0 before you get to 172.16.2.0 would be 172.16.1.255.

I cut alot of corners with charts, but if you need it, i can break this down to binary too.
just difficult to explain in a thread/forum.

thanks a bunch !
• Member Member Posts: 54 ■■■□□□□□□□
i was right...too much coffee+exhaustion=no comprehension of a relatively simple concept...i'm able to almost grasp the whole of subnetting now...i'm at the end of wendell odom's subnetting chapter and the last concept is " knowing how to choose a valid, classsful subnet "...doing better guys, thanks !....
• 1337sauce Member Posts: 1,571
I learned subnetting recently...took about 15 minutes and I can do it all in my head now

Should be helpful when going for some networking certs...
• Member Member Posts: 54 ■■■□□□□□□□
lsud00d wrote: »
I learned subnetting recently...took about 15 minutes and I can do it all in my head now

Should be helpful when going for some networking certs...

i hear those with a propensity for math and analytical thinking can learn these things quickly after being in the industry for awhile...for those like me, who were english majors and " math-dumb ", it takes awhile....
• Senior Member Member Posts: 556
lsud00d wrote: »
I learned subnetting recently...took about 15 minutes and I can do it all in my head now

Should be helpful when going for some networking certs...

Maybe you should share how you learned it in 15 minutes rather than gloating about it to the OP, who's having some difficulties with it
• Member Member Posts: 54 ■■■□□□□□□□
pham0329 wrote: »
Maybe you should share how you learned it in 15 minutes rather than gloating about it to the OP, who's having some difficulties with it

hey pham !...i didn't want to be ugly, but that's kind of how i felt...thanks for being the " voice of the voiceless ! "...anyways, i've got it all working now....thanks for all your input !....:)
• Network Engineer Member Posts: 1,363 ■■■■□□□□□□
Ryan,

I picked up subnetting in a short time simply because I did constant quizzes for a while. Can't say it was in 15 minutes though like the other guy. Glad you found your answer. Also one thing, I notice you are in Hampton, VA. Thats exactly where I live!! Are you attending the netacad program somewhere at a community college locally? I attended the netacad program at TNCC. Great place to learn the material with plenty of hardware
Currently reading: Network Warrior, Unix Network Programming by Richard Stevens
• Member Member Posts: 54 ■■■□□□□□□□
CodeBlox wrote: »
Ryan,

I picked up subnetting in a short time simply because I did constant quizzes for a while. Can't say it was in 15 minutes though like the other guy. Glad you found your answer. Also one thing, I notice you are in Hampton, VA. Thats exactly where I live!! Are you attending the netacad program somewhere at a community college locally? I attended the netacad program at TNCC. Great place to learn the material with plenty of hardware

thanks for the reply...i attended the netacademy courses at ECPI about six years ago, and i was a small computer systems specialist for 4 years in the marines ( you'd think i'd have this down by now ! )....yep, i have packet tracer and i'm able to comprehend subnetting completely now, it's just remembering the processes that is proving to be difficult...thanks for the reply !
• Senior Member Member Posts: 124
I went to a bootcamp and watched a video called subnetting made easy.
picked it up, and practiced it. learned to create my own little chart.
had it down in 2 days.

practice it over and over, and you get the hang of it. can subnet, supernet like its nothing.

memorize multiple s of 16 too. Cisco loves 16.

16, 32, 48, 64, 80, 96, 112, 128, 144, 160, 176, 192, 208, 224, 240, 256
nerd power.
• Member Member Posts: 80 ■■□□□□□□□□
why 16s?

dave
• Junior Member Member Posts: 23 ■□□□□□□□□□
I memorized multiples of 8, which is the same concept as 16. If you do that, you should be able to remember a lot of the key numbers for subnetting. xirtlook is right though, Cisco loves multiples of 16 (or 8, same thing) when giving you subnetting scenarios. I can tell you that they really didn't get into anything below /24 when I took the test a year and a half ago. That being said, I have used /22 and /23 subnets at work, so being comfortable with any subnetting scenario is important.
• Member Member Posts: 80 ■■□□□□□□□□
cheers was thinking of this in the car on the way home from work and realised it was a stupid question lol

makes so much scene now cheers
• Senior Member Member Posts: 124
cheers mate

sorry I'm american, and when I worked for Under Armour and provided remote support to people in Ireland and Amsterdam, that was the coolest thing to me. Hearing them say "cheers".
nerd power.
• Senior Member Member Posts: 307
If you or anyone ever has issues with subnetting in the future, I would recommend watching the 3 subnetting videos from CBT Nuggets. I was also lost by all the written explanations and after watching his videos, it was so much clearer. It takes a while in the beginning writing everything down, but after a little bit you begin to write less and less to get the problem done. I was at 7-8 minutes in the beginning but now I can knock em out in 2-3 minutes per problem. Jeremy Cioara is the man!
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