IP Addressing - Identify Broadcast Address

JLL · June 2006

I felt very comfortable with IP Addressing and Subnetting until I was referred to this site --> http://www.subnettingquestions.com/. Here is the first question I was asked

Question: What is the broadcast address of the network 172.28.208.0 255.255.252.0?

Answer: 172.28.211.255

Would anyone care to explain?

Thanks in advance.

Olajuwon · June 2006

It's correct
Default mask for a 172.16.0.0. 172.31.255.255 is 255.255.0.0
In 255.255.252.0
22 bits used for the subnet mask, leaving 10 bits for the host address
Network address is 172.28.0.0
subnets 2^6-2=62
hosts 2^10-2=1022
Valid subnets 256-252= 4, 8,...208..212..216...248
172.28.4.0, 172.28.8.0, 172.28.12.0.........172.28.248.0
172.28.208.0 is the net ID for the 172.28.208.0 subnet
1st host 172.28.208.1
last host is 172.28.211.254
broadcast address is 172.28.211.255
172.28.212.0 is the next subnet, so we stop before it

I hope you understand

JLL · June 2006

OK, after working the address again, my notes matched up with yours up until you say '172.28.208.0 is the net ID for the 172.28.208.0 subnet'. My understanding is that the 172.28 is the network ID for the .208 subnet ID. If this is true, then the following would be true wouldn't it?

172.28.208.0/22

172.28.208.1 - 172.28.208.254

172.28.208.255 is the broadcast address for the .208 subnetID

I don't know where in the calculations would you get a valid 172.28.211.0 when the grouping number is 4, hence 172.28.4.0, 172.28.8.0, 172.28.12.0 . . etc.

**** After staring at it for a while, I realized what I did and failed to do ****

I am now back at feeling very comfortable with IP Addressing and Subnetting!

Olajuwon · June 2006

You forgot about hte 3rd octet
172.28.208.0 is the subnet
172.28.208.1 is the first host
172.28.211.254 is the last host ( remember that the next subnet is 172.28.212.0)
Broadcast address is 172.28.211.255

You won't understand if you haven't mastered subnetting yet.

JLL · June 2006

I am currently using the Microsoft Self-Paced 70-291 book as my primary source of information. Do you know of any free reading material available online?

Thanks for your time.

Olajuwon · June 2006

You DO NOT want to learn how to subnet with a microsoft book, you will only know the basics with an MS book. Read the cisco white papers if you can't pick up a cisco subnetting book. [/b]

JLL · June 2006

I don't mind picking up a Cisco Subnetting book. Is there a specific one?

I found this --> http://www.cisco.com/warp/public/701/3.html

Olajuwon · June 2006

The sybex CCNA 4th edition book is very good. The link you found will give you a firm grip on subnetting.

shamrocker98 · June 2006

http://www.learntosubnet.com/

iankf · June 2006

Hey all,

I two thought I had a good understanding of subnets and subnet masks but going through this I'm totally confused as I used MS book and it all made sense as well as the learnkey, It seems I cant figure out the calculations for hosts/subnets. Also determining which ips are on the same subnets.

I've read through this a couple of times but just made me more baffled
http://www.cisco.com/warp/public/701/3.html

Any help?

iankf · June 2006

I found another great resource

http://www.ralphb.net/IPSubnet/

Now I understand

JLL · June 2006

Shamrocker, thank you for providing the link.

Iankf, join the club! I too read this --> http://www.cisco.com/warp/public/701/3.html and felt as if it didn't provide the breakdown detail I expected to see. Anyhow, I'll check out the link you provided a bit later.

If anyone has anymore resources, please share.

Thanks to all!

JLL · June 2006

This actually gets pretty good starting on page 9 of the actual document and not using the .PDF numbering --> http://www.3com.com/other/pdfs/infra/corpinfo/en_US/501302.pdf

IP Addressing - Identify Broadcast Address

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