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Home > Archive > CCNA > January 2003 > subnetting help.
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| e_mc2 2003-01-25, 12:37 am |
| Guys, I need someone who can give me some good explaination. Plz...just one min to explain to me.
I read many books about subnetting. I understand pretty clearly how to find # of subnet, # of host, Valid Subnet, Valid Host, and BroadCast address. Also, I could write down the whole table for Class A, B, C.
Of all the books, Cisco 607, Sybex 607, jumpstart 507, Exam Cheet 507, Cisco Track and some others. There is one thing that I did not see or I might missed it by reading too many book.
Most of the book explained by giving lot of example along w/ the Subnet Mask. As long as I have subnet mask. I can find everything but ......
1. What is network adddress for a host w/ Ip address 123.200.8.68/28 ?
2. Giving the network 192.141.27.0/28 what is the valid host?
3. What is the Broadcast Address for this Network 192.57.78.0/27?
I understand alot from reading it but just dont know how to use it for these questions.
I need good clear explanation plz.
thx a bunch in advance | |
| Imran4sin 2003-01-25, 6:42 am |
| Explaining all this would be no fun .. why dont you look through some of the earlier posts.. Questions like this have been asked lots of times.
Just go through the posts and i am sure u will find some regarding subnetting.
Those books that you mentioned.. they should be able to answer your questions in the first place!!!! | |
| davidbeecken 2003-01-25, 9:48 am |
| are you asking what the "/27" and the others mean? All that means is the number of masked bits in the subnet, ie "/8" is 11111111.00000000.0000000.00000000 or 255.0.0.0 and so on and so forth. Its just a block formation of writting the mask | |
| e_mc2 2003-01-25, 10:43 am |
| Hey Davidbeecken
Thx man...That is a big click in my head...I did not realize or pay attention to that /24 or /8 thing. That's why the whole world was confused.
I keep thinking how am I going to make subnet mask out from that Ip addrees or network address. W/ those binary you wrote down. Now I am a bomb!!!!
Sorry to be little too silly..But thx a lot for the help.. | |
| rjingra 2003-01-29, 10:02 am |
| e_mc2,
This is my first post so pls bear with me on this one...
I've been studying the 640-607 for several months, using the Sybex materials, the online ICND course thru KnowledgeNet, and the Cisco ICND. After all of this I still had a problem with "quickly" subnetting until I picked up a copy of the Cisco CCNA Exam 640-607 Certification Guide. Wendell Odom explains it better than anyone I've read thus far and now I believe I understand it and can do one in about 1-2 mins without binary!
He put it out there like this:
Network # :198 57 78 0
SubN Mask :255 255 255 224
SubN Numb :198 57 78 0
1st Valid IP:198 57 78 1
Broadcast :198 57 78 31
Last Val IP:198 57 78 30
1. So for this addr the mask ends in a # other than 255, so you subtract 256-224=32 (the magic # is the result).
2. To find the subnet, the subnet is the magic # multiplied by whatever to be less than or equal to the last octet of the ip. Since the ip ends in 0, then 32 can't be multiplied into it so the subnet is 0.
3. The 1st valid ip is 1 up from the subnet, the broadcast is 0+32-1=31 (subnet num + magic num - 1). Note the magic num is 256-what ever the last octet of the sub mask in this case 224=32).
4. The last valid IP is subnet-1=30.
A Magic # is only used if the last octet of the mask ends in something other than 0. If the mask ends in 0 say, then it would work out like this:
198.57.78.0 Network #
255.255.255.0 SNet Mask
198.57.78.0 SNet #
198.57.78.1 1st Valid IP
198.57.78.255 Broadcast
198.57.78.254 Last Valid IP
you can pick up a copy of the book described earlier, isbn 1-58720-055-4, you'll get the gist of what I'm talking about. After reading this book I can almost do most of the calculations in my head...
Does any of this make sense to you? If not pls email me and I might be able to send you some info that will explain it better. Hope this helped... Robert  | |
| rjingra 2003-01-29, 10:13 am |
| e_mc2 I messed up on my orig post. Under item 4, the Last valid ip is the broadcast minus 1, not subnet minus 1 and typed. My bad...
quote:
Originally posted by rjingra
e_mc2,
This is my first post so pls bear with me on this one...
I've been studying the 640-607 for several months, using the Sybex materials, the online ICND course thru KnowledgeNet, and the Cisco ICND. After all of this I still had a problem with "quickly" subnetting until I picked up a copy of the Cisco CCNA Exam 640-607 Certification Guide. Wendell Odom explains it better than anyone I've read thus far and now I believe I understand it and can do one in about 1-2 mins without binary!
He put it out there like this:
Network # :198 57 78 0
SubN Mask :255 255 255 224
SubN Numb :198 57 78 0
1st Valid IP:198 57 78 1
Broadcast :198 57 78 31
Last Val IP:198 57 78 30
1. So for this addr the mask ends in a # other than 255, so you subtract 256-224=32 (the magic # is the result).
2. To find the subnet, the subnet is the magic # multiplied by whatever to be less than or equal to the last octet of the ip. Since the ip ends in 0, then 32 can't be multiplied into it so the subnet is 0.
3. The 1st valid ip is 1 up from the subnet, the broadcast is 0+32-1=31 (subnet num + magic num - 1). Note the magic num is 256-what ever the last octet of the sub mask in this case 224=32).
4. The last valid IP is subnet-1=30.
A Magic # is only used if the last octet of the mask ends in something other than 0. If the mask ends in 0 say, then it would work out like this:
198.57.78.0 Network #
255.255.255.0 SNet Mask
198.57.78.0 SNet #
198.57.78.1 1st Valid IP
198.57.78.255 Broadcast
198.57.78.254 Last Valid IP
you can pick up a copy of the book described earlier, isbn 1-58720-055-4, you'll get the gist of what I'm talking about. After reading this book I can almost do most of the calculations in my head...
Does any of this make sense to you? If not pls email me and I might be able to send you some info that will explain it better. Hope this helped... Robert
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| e_mc2 2003-01-30, 12:44 am |
| thx again buddy for give me right info...I am now through w/ it...read it for 4 days straight.....using 4 different books.. Everything is making sense now.
LOL |
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