Skip navigation
Login   |   Register
Cisco Learning Home > Certifications > Routing & Switching (CCNA) > Discussions

_Communities

This Question is Answered
19511 Views 6 Replies Latest reply: Jan 30, 2011 6:06 AM by Fabri RSS

Currently Being Moderated

QUICKLY CALCULATE THE SUMMARY ROUTE

Jan 29, 2011 2:51 PM

Fabri 205 posts since
Aug 12, 2010

hello guys,
I want to learn how to calculate the summary route quickly, without having to convert to binary IP address.
if not mistaken it is estimated multiple contiguous networks of 4 ... but I did not understand ... can anyone help me?

  • Martin 13,892 posts since
    Jan 16, 2009
    Currently Being Moderated
    1. Jan 29, 2011 3:14 PM (in response to Fabri)
    Re: QUICKLY CALCULATE THE SUMMARY ROUTE

    search for a post by John

    he had posted some examplses with explanations of decimal way to summerize

    Join this discussion now: Login / Register
  • Martin 13,892 posts since
    Jan 16, 2009
    Currently Being Moderated
    2. Jan 29, 2011 3:14 PM (in response to Martin)
    Re: QUICKLY CALCULATE THE SUMMARY ROUTE
    Join this discussion now: Login / Register
  • Brian 2,971 posts since
    Aug 17, 2009
    Currently Being Moderated
    3. Jan 29, 2011 3:23 PM (in response to Fabri)
    Re: QUICKLY CALCULATE THE SUMMARY ROUTE

    Aloha Fabri,

     

    There is no trick to doing this quickly unless you have already memorized certain prefix lengths and subnet mask relationships.

     

    Also, this depends on the networks you wish to summarize.  For example, summarize the following three Class C addresses?

     

    192.168.0.0/24

    192.168.2.0/24

    192.168.3.0/24

     

    Answer: 192.168.0.0/22

    Note this summary address includes the 192.168.1.0/24 network which may or may not belong to you.

     

    summarize the following 10 network?

     

    172.16.2.0/24

    172.16.3.0/24

    172.16.4.0/24

    172.16.5.0/24

    172.16.6.0/24

    172.16.7.0/24

    172.16.8.0/24

    172.16.9.0/24

    172.16.10.0/24

    172.16.11.0/24

     

    Answer:  172.16.0.0/20

    Note this summary address covers 172.16.0.0 to 172.16.15.255 and includes address not identified or that may not belong to you.  A an alternate summarization you could do the following:

     

    172.16.2.0/23   --> cover 172.16.2.0/24 and 172.16.3.0/24

    172.16.4.0/22   --> covers 172.16.4.0/24 to 172.16.7.0/24

    172.16.8.0/22   --> covers 172.16.8.0/24 to 172.16.11.0/24

     

    With the second summary example you do not include addresses that are not shown.  But either way is correct summarization.

     

    Here is a little something that may help you in summarizing (supernetting)

     

    /24 = 1 network

    /23 = 2 networks

    /22 = 4 networks

    /21 = 8 networks

    /20 = 16 networks

    /19 = 32 networks

    /18 = 64 networks

    /17 = 128 networks

    /16 = 256 networks.

     

    this of course only applies to networks with a /24 prefix or subnet mask of 255.255.255.0.  But hopefully this will help you.

     

    HTH

    Join this discussion now: Login / Register
  • Brian 2,971 posts since
    Aug 17, 2009
    Currently Being Moderated
    4. Jan 29, 2011 3:30 PM (in response to Martin)
    Re: QUICKLY CALCULATE THE SUMMARY ROUTE

    Nice find Martin.  Thanks John, very good reading.

     

    Join this discussion now: Login / Register
  • Conwyn 9,667 posts since
    Sep 10, 2008
    Currently Being Moderated
    5. Jan 30, 2011 12:55 AM (in response to Fabri)
    Re: QUICKLY CALCULATE THE SUMMARY ROUTE

    Hi Fabri

     

    You need to learn your sixteen times table and then visualize the subnets.

     

    So say you had 10.0.3.0   and 10.0.17.0     then you can see it falls either side of 16 but not 32.

     

    If you learn your 16 times table then you learn your 32 times up to 8 which is all you need.

     

    so the summary is 10.0.0. to 10.0.64.0 - 1     

     

    so 64 is 2 to the six so the summary is 10.0.0.0/(24-6) or 10.0.0.0/18.

     

    Regards Conwyn

    Join this discussion now: Login / Register

Actions

More Like This

  • Retrieving data ...

Bookmarked By (1)