Route Summarization

Tommy2727Tommy2727 Member Posts: 48 ■■□□□□□□□□
Greeting all,

Please can some one answer this question for me!!!

From the summarized IP address 192.168.176.0/21 the range of IP addresses available to receive packets are 192.168.176.1 through 192.168.183.254.. WHY

By the way this has to do with route summarization..... .......ok.........I know the /21 has 32 subnets and 2,048 hosts per subnet but where I'm getting confused is the range of networks that will be routed to or from....... 176.1 ~ 183.254, That's not 32 subnets.
networks only in those ranges will receive packets from the adjacent router. UGH!!

How did todd lammle get that ranage? 192.168.176.1 through 192.168.183.254 summarized IP 192.168.176.0/21



Appreciation in advance, Thks.
Practice, Practice, and more Practice make Perfection.....

Comments

  • networker050184networker050184 Mod Posts: 11,962 Mod
    Look at it in binary. 192.168.176.0/21 = 192.168.176.0 - 192.168.183.255
    An expert is a man who has made all the mistakes which can be made.
  • Tommy2727Tommy2727 Member Posts: 48 ■■□□□□□□□□
    How? Brake down the summarized route then coorelate with the valid network ranges?
    Practice, Practice, and more Practice make Perfection.....
  • networker050184networker050184 Mod Posts: 11,962 Mod
    Tommy2727 wrote: »
    How? Brake down the summarized route then coorelate with the valid network ranges?


    Don't worry about network ranges. If you look at the binary that address and mask encompasses all those addresses. Not sure what you are confused about.
    An expert is a man who has made all the mistakes which can be made.
  • CyanicCyanic Member Posts: 289
    192.168.176.0 tells you where to start, and /21 tells you how far up to go.
  • Tommy2727Tommy2727 Member Posts: 48 ■■□□□□□□□□
    O, Ok. I'm do the binary conversion now to test the theory.
    Practice, Practice, and more Practice make Perfection.....
  • SelfmadeSelfmade Member Posts: 268
    Cyanic wrote: »
    192.168.176.0 tells you where to start, and /21 tells you how far up to go.

    +rep, that's exactly the best explaination for it, it can't get any simpler than that. At first, even as simple as it is, it can be confusing to someone who overthinks it icon_redface.gif
    It's not important to add reptutation points to others, but to be nice and spread good karma everywhere you go.
  • shaqazoolushaqazoolu Member Posts: 259 ■■■■□□□□□□
    Only because I'm bored...

    /21 means you borrow 3 network bits from the third octet. Since addresses are done in powers of 2, you take 2^3=8. Now we look at the third octet again. To find the network address, you simply keeping adding by increments of 8 (calculated earlier) until you find the number that is closest to the third octet without going over. In this case it is 176 on the dot.

    That gives us our network address (192.168.176.0), and therefore the first usable IP(192.168.176.1). Take the first number we calculated [8] and add it to that address (176+8=184) to find the next network address (192.168.184.0). Since that network address starts the next summary, you take one away to find our broadcast address (192.168.183.255) and therefore our last usable IP address (192.168.183.254).

    Viola! 192.168.176.1 - 192.168.183.254

    That's how I do it in my head anyway...
    :study:
  • mella060mella060 Member Posts: 196
    Basically a /21 means that your increment is 8 and in the 3rd octet.

    So your networks are...

    192.168.0.0
    192.168.8.0
    192.168.16.0
    ...
    ...
    192.168.176.0
    192.168.184.0


    That is where the range is coming from
  • tech-airmantech-airman Member Posts: 953
    Tommy2727 wrote: »
    Greeting all,

    Please can some one answer this question for me!!!

    From the summarized IP address 192.168.176.0/21 the range of IP addresses available to receive packets are 192.168.176.1 through 192.168.183.254.. WHY

    By the way this has to do with route summarization..... .......ok.........I know the /21 has 32 subnets and 2,048 hosts per subnet but where I'm getting confused is the range of networks that will be routed to or from....... 176.1 ~ 183.254, That's not 32 subnets.
    networks only in those ranges will receive packets from the adjacent router. UGH!!

    How did todd lammle get that ranage? 192.168.176.1 through 192.168.183.254 summarized IP 192.168.176.0/21



    Appreciation in advance, Thks.

    Tommy2727,

    For 192.168.176.0, what class is that IP network address?
  • Tommy2727Tommy2727 Member Posts: 48 ■■□□□□□□□□
    Tommy2727,

    For 192.168.176.0, what class is that IP network address?
    All thanks so much that seemed very simple now that you've explained like that that - WOW!!!! I feel like such a dusch lol.. that's was basic subnetting... Again all I appreciate the time and effort you took in helping a fellow CCNA candidate...

    Tech-airman to answer your question 192.168.176.0 is actually a class C IP address however in the above examples the mask associated with, /21 which puts that specific IP route summary address in the class B category..

    Cheers and thanks again.
    Practice, Practice, and more Practice make Perfection.....
  • alan2308alan2308 CISSP, MCSA 2008, MCSA 2012, CCNA R&S, CCNA Security Ann Arbor, MIMember Posts: 1,854 ■■■■■■■■□□
    Tommy2727 wrote: »
    All thanks so much that seemed very simple now that you've explained like that that - WOW!!!! I feel like such a dusch lol.. that's was basic subnetting... Again all I appreciate the time and effort you took in helping a fellow CCNA candidate...

    Tech-airman to answer your question 192.168.176.0 is actually a class C IP address however in the above examples the mask associated with, /21 which puts that specific IP route summary address in the class B category..

    Cheers and thanks again.

    You might want to review Classful networks.
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