Route Summarization For Dummies 1

[ts8586]

The dummy being me... Are there any good articles/lessons out there that explain it? I understand (for the most part) block sizes, just having a hard time applying the concept to route summarizations. Thanks for your time!

 

[ts8586]

Okay, here's what I'm specifically having a problem with:

access-list 10 permit 172.29.16.0 0.0.0.255
access-list 10 permit 172.29.17.0 0.0.0.255
access-list 10 permit 172.29.18.0 0.0.0.255
access-list 10 permit 172.29.19.0 0.0.0.255

Here's what I'm thinking, and I'm guessing I'm wrong...
Starting at .16.0, going up in blocks of 4 would take me to 172.29.19.0? And that's a block of 4, correct?
So I'm guessing that the answer would be

access-list 10 permit 172.29.16.0 0.0.3.255

Am I close?

 

[burtsbees]

I don't understand the question...what exactly are you asking?
Are you asking what acl can do al the 172.29.16.0/24 though 172.29.19.0???

Burt

 

[Ronster]

From my understanding the router(s) that use the same route for:
172.29.16.0 0.0.0.255
172.29.17.0 0.0.0.255
172.29.18.0 0.0.0.255
172.29.19.0 0.0.0.255

Can summarize all these routes to:
172.29.16.0/22

In Binary:
[red]10101100.00011101.000010[/red][blue]00.00000000[/blue]
Thru:
[red]10101100.00011101.000010[/red][blue]11.11111111[/blue]

The bits in red are common and the summarization of the range of IP addresses above. The blue bits can be anything as any IP address matching the red bits are permitted.

So, to save routing table space, the router holds 1 route for 172.29.16.0/22 rather than 4 individual routes for the subnetworks:
172.29.16.0 0.0.0.255
172.29.17.0 0.0.0.255
172.29.18.0 0.0.0.255
172.29.19.0 0.0.0.255

Ronster

Science is the rehab of the masses.

 

[Ronster]

The subnet mask would be:
172.29.19.0 0.0.3.255

Ronster

Science is the rehab of the masses.

 

[Ronster]

Ooops!
Last post should read...

The subnet mask would be:
172.29.16.0 0.0.3.255

Easy to make these mistakes. Always check your work ;-)

Ronster

Science is the rehab of the masses.

 

[ts8586]

Sorry I wasn't clear with me question, Burtsbees. Thanks Ronster, I think I have it figured out.

 

[Ronster]

Glad I could be of help TS.

And of course 0.0.3.255 is the wildcard NOT a subnet mask.

Thanks for the

Ronster

Science is the rehab of the masses.

 

[Slabs]

Can summarize all these routes to:
172.29.16.0/22

In Binary:
10101100.00011101.00001000.00000000
Thru:
10101100.00011101.00001011.11111111


The binary is wrong in the 3rd Octet with should be 16
00001000 = 8
should read 00010000.

Same for 3rd Octet on 2nd line
00001011 = 11
should read 00010011

Summarization remains correct though