Options

Summary address

MikdillyMikdilly Member Posts: 309
What is the best summary route for the addresses 172.17.192.0/24 through 172.17.207.0/24?

In the third octet I get:

11000000
11000111

which gives a boundary between 5th and 6th bit.

So summary address i come up with is 172.17.192 /21 but this doesn't appear correct as it doesn't include all addresses between 192 and 207, but /20 does. Are there times when you might have to adjust the mask?

Comments

  • Options
    NetstudentNetstudent Member Posts: 1,693 ■■■□□□□□□□
    11000111 = 199

    11001111 = 207

    thats what happened. I don't think you were using the right binary bit combination to derive the correct summary mask. Here you will see the boundry between the 4th and 5th bit, thus giving you a /20.
    There is no place like 127.0.0.1 BUT 209.62.5.3 is my 127.0.0.1 away from 127.0.0.1!
  • Options
    MikdillyMikdilly Member Posts: 309
    Netstudent wrote:
    11000111 = 199

    11001111 = 207

    thats what happened. I don't think you were using the right binary bit combination to derive the correct summary mask. Here you will see the boundry between the 4th and 5th bit, thus giving you a /20.

    Thanks, guess I've been going at this for too long today.
  • Options
    PashPash Member Posts: 1,600 ■■■■■□□□□□
    Mikdilly wrote:
    Netstudent wrote:
    11000111 = 199

    11001111 = 207

    thats what happened. I don't think you were using the right binary bit combination to derive the correct summary mask. Here you will see the boundry between the 4th and 5th bit, thus giving you a /20.

    Thanks, guess I've been going at this for too long today.

    But you should be happy that you know this inside out now! :)

    Good luck.
    DevOps Engineer and Security Champion. https://blog.pash.by - I am trying to find my writing style, so please bear with me.
  • Options
    Tricon7Tricon7 Inactive Imported Users Posts: 238
    Btw, what's a quicker way of determining the summary address for a problem like this instead of writing out in binary all numbers between 192 and 207 to see what they all have in common? I won't have that kind of time for a cert. test.
  • Options
    PashPash Member Posts: 1,600 ■■■■■□□□□□
    Tricon7 wrote:
    Btw, what's a quicker way of determining the summary address for a problem like this instead of writing out in binary all numbers between 192 and 207 to see what they all have in common? I won't have that kind of time for a cert. test.

    Not really a quicker way, You find the interesting octet, ie where the binary's don't match and then find the boundary.
    DevOps Engineer and Security Champion. https://blog.pash.by - I am trying to find my writing style, so please bear with me.
  • Options
    NetstudentNetstudent Member Posts: 1,693 ■■■□□□□□□□
    What i like to do is first, look at the first subnet number and last subnet number. Like in this case 192 through 207. That is the range you need to cover. So what is the difference between 207 and 192? It's 15. So is there a block that covers 15? NO, but there is a block that covers 16. So now you need to know if 192 is divisible by 16. IF it is then it makes your problem really easy. IN this case it is, so you know your summary address will be 172.17.192.0. NOw what mask gives you a block of 16? YOu should know that a 240 has to be in there somewhere because 256-240 = 16. And since we are talking about the 3rd octet here, your mask will be 255.255.240.0.
    There is no place like 127.0.0.1 BUT 209.62.5.3 is my 127.0.0.1 away from 127.0.0.1!
  • Options
    mobri09mobri09 Users Awaiting Email Confirmation Posts: 723
    Netstudent wrote:
    What i like to do is first, look at the first subnet number and last subnet number. Like in this case 192 through 207. That is the range you need to cover. So what is the difference between 207 and 192? It's 15. So is there a block that covers 15? NO, but there is a block that covers 16. So now you need to know if 192 is divisible by 16. IF it is then it makes your problem really easy. IN this case it is, so you know your summary address will be 172.17.192.0. NOw what mask gives you a block of 16? YOu should know that a 240 has to be in there somewhere because 256-240 = 16. And since we are talking about the 3rd octet here, your mask will be 255.255.240.0.

    Nicely said Netstudent! Thanks for the help! :D
  • Options
    dtlokeedtlokee Member Posts: 2,378 ■■■■□□□□□□
    Yeah really, a subnet address is nothing more than a summary address for a bunch of host addresses icon_exclaim.gif If you think of it in those terms you may seem to have an easier time of it.
    The only easy day was yesterday!
  • Options
    mobri09mobri09 Users Awaiting Email Confirmation Posts: 723
    I agree....I always seem to make things harder than they really are -
Sign In or Register to comment.