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  1. Junior Member Registered Member
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    #251
    Quote Originally Posted by veritas_libertas View Post
    Yes 192.168.10.1 is the subnet.

    There is nothing to subtract since /24 = a Class C network = 255.255.255.0 Since /24 is not being divided up, i.e. none of the eight host bits are being switched over to network bits 11111111.111111111.11111111.00000000 there is on the /24 network. 1-254 being the hosts with 0 being the network and 255 being the broadcast address.

    Does that help?
    I am trying to set up a router using FastEthernet0/0 to connect to another routers FastEthernet0/0

    I tried using this command:

    Router0(config-if)#ip address 192.168.10.1 192.168.10.0
    Bad mask 0xC0A80A00 for address 192.168.10.1

    and get this Bad mask error. Isnt this the subnet mask 192.168.10.0 for 192.168.10.1?
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    #252

    Default My answer

    Quote Originally Posted by kriscamaro68 View Post
    Ok so I got this question on subnettingquestions.com and didn't see a way to answer it with your method: Question: You are designing a subnet mask for the 10.0.0.0 network. You want 3800 subnets with up to 3800 hosts on each subnet. What subnet mask should you use? Answer: 255.255.240.0 Here is also another one: Question: How many subnets and hosts per subnet can you get from the network 172.29.0.0 255.255.254.0? Answer: 128 subnets and 510 hosts Any way of explaining that out in your method. Thanks for that post I am finally starting to get subnetting.
    always when you are doing these questions make sure,you meet the requirement of the customer. for the first question the requirement was 3800 subnet and 3800 host. for subnet make sure that you find power of 2,that is greater than or equal to number of subnet required 2^n>=3800. where n is the number of bits that have bee turn on. we get n equal to 12 that will be 4096 subnets in total. hence 12 will help to find the subnet mask and to check if number of host will be sufficient . this 12 is needed to set the left most bits of default mask(given mask) from zeros to ones, i.e to turn on the bits hence the subnet mask will be:- from default 255.0.0.0 in binaary 11111111.00000000.00000000.00000000 hence put those 12 bits in a subnet mask 11111111.11111111.11110000.00000000 in decimal 255.255.240.0 from this subnet will get 4094 hosts that is ( 2^f)-2 =4094 where f is the number of zeros from the subnet mask you found. 255.255.240.0. for question 2: for this question you didn't given number of subnets and hosts,just you just required to find them so to find this question,you have to work with subnet mask. from the subnet mask given 255.255.254.0 in binary numbers 11111111.11111111.11111110.00000000 so To number of host is =2^f -2 where f is number of zeros in a subnet mask. hence 2^9 -2= 510,the number of hosts. Easy to find number of subnet,we should look on class of the ip address given. the ip address is in class B, It's default subnet mask is 255.255.0.0. Hence from given subnet mask 255.255.254.0, It is seems like 7 bits have been turn on from default subnet mask. hence number of subnet will be 2^n, whrere n is the number of bits that have been turn on. 2^7=128. hence your answer are 128 number of subnets and 510 number of hosts
    Last edited by fadhil; 04-26-2012 at 10:16 PM.
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    #253
    Quote Originally Posted by knightrider56 View Post
    I am trying to set up a router using FastEthernet0/0 to connect to another routers FastEthernet0/0

    I tried using this command:

    Router0(config-if)#ip address 192.168.10.1 192.168.10.0
    Bad mask 0xC0A80A00 for address 192.168.10.1

    and get this Bad mask error. Isnt this the subnet mask 192.168.10.0 for 192.168.10.1?
    No, your subnet is .0 but your mask is 255.255.255.0
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  5. Audentis Fortuna Iuvat veritas_libertas's Avatar
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    #254
    Quote Originally Posted by knightrider56 View Post
    I am trying to set up a router using FastEthernet0/0 to connect to another routers FastEthernet0/0

    I tried using this command:

    Router0(config-if)#ip address 192.168.10.1 192.168.10.0
    Bad mask 0xC0A80A00 for address 192.168.10.1

    and get this Bad mask error. Isnt this the subnet mask 192.168.10.0 for 192.168.10.1?
    I don't mean to be insulting, but are you using a book to guide you through studying? If not you are only going to get confused and frustrated. We are more than glad to help, and I don't mean to make you feel otherwise.
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    #255

    Post my approach

    you didn't write the subnet mask,that's why an error occurred. the subnet mask looks like 255.225.255.xxxxxxxxx for class C ip address . you were suppose to configure like 198.168.10.1 255.255.255.xxxxxxxxx
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    #256

    Default Milestone Reached!

    For a very long time I have worked on mastering subnetting. I have tried many techniques and this method is ninja fast! I took notes, wrote out powers, masks, and any notes I needed and I can't tell you how blown away I am. I can burn through subnetting questions now. It is laughable now. A giant click happened with practicing and really poring over mistakes I made. I feel confident that I have subnetting 90% mastered. I need more practice with VLSM. Examples with multiple subnets and multiple host requirements are what I need to practive. I really feel confident about subnetting now! dear lord! It's like a giant dawning!

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    #257

    Post My answer

    The question is long but it is simple and has many approaches to reach to the answer/conclusion. you can use subneting only or subnetting and VLSM to solve the problem because both ways meet the requirements of a customer.
    thank u.
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    #258
    Is this site a good place to practice this method of subnetting? If not, know of any better ones?
    Last edited by FLEOHB; 04-29-2012 at 07:42 PM.
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    #259
    Quote Originally Posted by FLEOHB View Post
    Is this site a good place to practice this method of subnetting? If not, know of any better ones?
    Yes! Many people on here use it including myself. Brilliant place to practice!
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    #260
    Sweet, thanks MAC_Addy
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  12. Senior Member LinuxRacr's Avatar
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    #261
    Awesome! I have something similar from ##########.net in the form of an iPhone app.
    My WGU B.S. IT - Security Progress : Transferred In|Remaining|In Progress|Completed
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    #262
    Having trouble understanding the following question:

    You have subnetted the 192.168.14.0 network into 8 subnets. What is the valid host range of the third subnet?
    Answer: 192.168.14.65 - 192.168.14.94
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    WFV1, BNC1, EAV1, EBV1, COV1 | MGC1, IWC1 | CQV1, CNV1, IWT1, RIT1 | DRV1, DSV1, TPV1, CVV1 | EUP1, EUC1, DHV1| CUV1, C173 | BOV1, CJV1, TXP1, TXC1 | TYP1, TYC1, SBT1, RGT1 (84 CUs) DONE!
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    #263
    Quote Originally Posted by LinuxRacr View Post
    Having trouble understanding the following question:

    You have subnetted the 192.168.14.0 network into 8 subnets. What is the valid host range of the third subnet?

    Answer: 192.168.14.65 - 192.168.14.94
    First think about how many bits you need to create 8 subnets. 3 bits will do that. So that means your increment will be 32.

    1st subnet 0 - 31 - valid host range 1 through 30
    2nd subnet 32 - 63 - valid host range 33 through 62
    3rd subnet 64 - 95 - valid host range 65 through 94
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  15. Senior Member LinuxRacr's Avatar
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    #264
    Quote Originally Posted by j-man View Post
    First think about how many bits you need to create 8 subnets. 3 bits will do that. So that means your increment will be 32.

    1st subnet 0 - 31 - valid host range 1 through 30
    2nd subnet 32 - 63 - valid host range 33 through 62
    3rd subnet 64 - 95 - valid host range 65 through 94
    The red text above introduced a new concept to me to try to understand or reverse-engineer...

    If the increment is 32, then that means that 2^5 is the blocksize, or increment. That means to get that, since this is a class C address default mask, we had to subtract 27 from 32 boundary to get the 5 to plug into 2^5. So by this logic, the CIDR is /27. The three bits you are referring to are the extra bits added past the /24 CIDR boundary.

    Now my question is how did you figure out that 3 bits would work so quickly?
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    #265
    The question stated that we subnetted that class C network into 8 subnets. 2^3 = 8

    The resulting subnet mask for that network would be 255.255.255.224 or in binary

    11111111.11111111.11111111.11100000 The bits with 1 are the number of subnets created with this class C mask and the 0 bits are the number of hosts - 2 (2^5 - 2) or 30 because remember that the subnet number and broadcast are not usuable for hosts.
    Last edited by j-man; 05-18-2012 at 06:04 PM.
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  17. Senior Member jamesp1983's Avatar
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    #266
    Excellent technique. I have always enjoyed the dotted decimal method (256 - value present in interesting octet). Once you understand subnetting keep practicing it. You need to be fast and accurate at this.
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  18. Senior Member jamesp1983's Avatar
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    #267
    Quote Originally Posted by Tfoote01 View Post
    For a very long time I have worked on mastering subnetting. I have tried many techniques and this method is ninja fast! I took notes, wrote out powers, masks, and any notes I needed and I can't tell you how blown away I am. I can burn through subnetting questions now. It is laughable now. A giant click happened with practicing and really poring over mistakes I made. I feel confident that I have subnetting 90% mastered. I need more practice with VLSM. Examples with multiple subnets and multiple host requirements are what I need to practive. I really feel confident about subnetting now! dear lord! It's like a giant dawning!


    Congrats! It is an excellent feeling once you get it.
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  19. Senior Member LinuxRacr's Avatar
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    #268
    Thanks for the explanation. This is adding to the angles of attack in my subnetting arsenal.
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  20. Member radix's Avatar
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    #269
    Having trouble how to answer these question from Lammle's book

    You have a Class B network and need 29 subnets. What is your mask?
    Answer: 255.255.248.0

    is there a way to solve this or do we need to memorize the netmask?
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    #270
    Quote Originally Posted by radix View Post
    is there a way to solve this or do we need to memorize the netmask?
    You can use my chart if you want.

    But just remember that Class B you can count from:

    255.255.0.0 = 1 subnet
    255.255.128.0 = 2 subnets
    255.255.192.0 = 4 subnets
    255.255.224.0 = 8 subnets
    255.255.240.0 = 16 subnets
    255.255.248.0 = 32 subnets
    255.255.252.0 = 64 subnets
    255.255.254.0 = 128 subnets

    That's how I figure out how many subnets for each class.
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    #271
    Quote Originally Posted by MAC_Addy View Post
    You can use my chart if you want.

    But just remember that Class B you can count from:

    255.255.0.0 = 1 subnet
    255.255.128.0 = 2 subnets
    255.255.192.0 = 4 subnets
    255.255.224.0 = 8 subnets
    255.255.240.0 = 16 subnets
    255.255.248.0 = 32 subnets
    255.255.252.0 = 64 subnets
    255.255.254.0 = 128 subnets

    That's how I figure out how many subnets for each class.
    oooh thanks will be a great help
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    #272
    subnetting is easy. you just have to memorize the increments.
    128+64+32+16+8+4+2+1 = 128, 192, 224, 240, 248, 252, 254, 255 <---- MEMORIZE
    now all you have to do is the grade 3 math. 256-increment # (for example 256-224 = 32)

    EX:
    network: 192.168.0.0 /27 (/27 = 255.255.255.224) 256- 224 = 32 (subnets will be 0, 32, 64, 96....224)
    1st subnet: 192.168.0.0 - 192.168.0.31
    2nd subnet: 192.168.0.32 - 192.168.0.63
    3rd subnet: 192.168.0.64 - 192.168.0.95

    etc...

    hope this helps.
    Last edited by ricky8; 05-30-2012 at 05:04 AM.
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  24. Junior Member Noerc's Avatar
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    #273
    Thanks for sharing, I havn't been great at subnetting but the more I read and practice it all comes together!
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  25. Senior Member LinuxRacr's Avatar
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    #274
    Anyone have a good method for figuring out which mask for each class will give you a given number of subnets when only the IP is available?
    Last edited by LinuxRacr; 06-01-2012 at 08:37 PM.
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    #275
    That kind of defeats the purpose of the subnetting... if given no subnet mask then you will use the default class mask for the range of IP's

    then it's business as usual

    I'm sure you can find a cheat sheet somewhere given the range and available masks and the numbers it produces.

    This comes to mind

    http://www.aelius.com/njh/subnet_sheet.html
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