Route Summarization

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

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

Practice, Practice, and more Practice make Perfection.....

• 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.
• Member Posts: 48 ■■□□□□□□□□
How? Brake down the summarized route then coorelate with the valid network ranges?
Practice, Practice, and more Practice make Perfection.....
• Mod Posts: 11,962 Mod
Tommy2727 wrote: »
How? Brake down the summarized route then coorelate with the valid network ranges?

An expert is a man who has made all the mistakes which can be made.
• Member Posts: 289
192.168.176.0 tells you where to start, and /21 tells you how far up to go.
• Member Posts: 48 ■■□□□□□□□□
O, Ok. I'm do the binary conversion now to test the theory.
Practice, Practice, and more Practice make Perfection.....
• 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
It's not important to add reptutation points to others, but to be nice and spread good karma everywhere you go.
• 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:
• Member Posts: 196
Basically a /21 means that your increment is 8 and in the 3rd octet.

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
• Member Posts: 953
Tommy2727 wrote: »
Greeting all,

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

Tommy2727,

For 192.168.176.0, what class is that IP network address?
• 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.....
• 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.