route summarization

ayosizzle · ‎02-02-2012

Olla,

was actually reading up on route summarization and i just got myself all confused. the question goes thus:

Summarize the following range:

10.16.31.0/24

10.16.32.0/24

10.16.33.0/24

10.16.34.0/24

10.16.35.0/24

10.16.36.0/24

10.16.37.0/24

10.16.38.0/24

10.16.39.0/24

10.16.40.0/24

After my calculations i supposed the answer would be 10.16.0.0/18 but the exercise said my answer was wrong coz of watsed addresses. Can anyone clarify or explain this?? and also provide more examples i can refer back to.

Regards,

DJ.

jamiegrive · ‎02-02-2012

Hi,

You can summarise 32.0 through to 39.255 quite nicely using 10.16.32.0 /21 (8 networks). Then you need to add the individual /24's that can not fit within a summary without summarising networks you do not own.

Do you understand my logic here or shall I expand further? Please don't hesitate to ask.

10.16.31.0/24 - Individual /24

10.16.32.0/24 - Part of 32.0/21

10.16.33.0/24 - Part of 32.0/21

10.16.34.0/24 - Part of 32.0/21

10.16.35.0/24 - Part of 32.0/21

10.16.36.0/24 - Part of 32.0/21

10.16.37.0/24 - Part of 32.0/21

10.16.38.0/24 - Part of 32.0/21

10.16.39.0/24 - Part of 32.0/21

10.16.40.0/24 - individual /24

Regards,

Jamie

Sent from Cisco Technical Support iPhone App

Oleksandr Nesterov · ‎02-06-2012

Hi Dj

Here is binary translaion of the third octet:

31 -	00011111
32 -	00100000
33 -	00100001
34 -	00100010
35 -	00100011
36 -	00100100
37 -	00100101
38 -	00100110
39 -	00100111
40 -	00101000

So you can see that addresses from 32 to 39 (first 5 bits of the third octet are the same 00100 ) can be summarized under the same prefix 21.

Addresses 31 and 40 should be dvertised separately.

By reducing mask size you will include unused networks whic will be wasted.

HTH,

Alex