Cisco Router Summarization

[rameunknown]

This was an awesome explanation. Keep it up buddy.

[arifsali]

Hi Keith, thank you so much for this.

I just wish to make sure and confirm: from the left, you "add" the bits which are matching among all routes (1 0 0 is matching and it adds up to 128 in this example) and that would be part of the summary route? If you had 1 1 as a common bit among all routes, that would be 192. So on and so forth. If this is correct, than that's beautiful.

But I am still struggling to figure out how you arrived at the subnet mask of 27?

[arifsali]

Oh, oh, oh, never mind, I think I just understood where 27 is coming from. The 27 represent x (8). x (16). x (24) and 1 0 0 (27). :)

[Keith6783]

@arifsali

You are right on the math.

100 if those were the 3 high order common bits, it would be 128

101 if those were the 3 high order common bits, it would be 160

etc.

Best wishes,

Keith

[hedgeduck1]

you're intro drives me crazy

[miszczpolska]

Lets take as an example the range of IPs 172.16.128.0-172.16.159.255 We see that the network mask will have to affect 3rd octet. The easy way it to subtract 128 from 159. Lets see 159-128=31 Now subtract 31 from 255 255-31=224 There we go, this is our 3rd octet in the subnet mask 172.16.128.0 255.255.224.0 Another example Summarize networks 100.16.0.0 100.17.0.0 100.18.0.0 100.19.0.0 19-16=3 255-3=252 Our subnet mask is 255.252.0.0 for network 100.16.0.0

[Keith6783]

@miszczpolska

Thanks for the great additional information!

Best wishes,

Keith

[miszczpolska]

@Keith6783 thanks!. I am studying for CCNA and network summarization was confusing me a bit. I figured it out similar way as with subnetting and finding the block size, etc /29... 32-29=3 (the power). 2^3=8 =block size. Or /29 is 255.255.255.248. Subtract 248 from 255 gives 8 as well, but easier way.

[MadProd209]

Hi Keith,

Great video so one question what about if I add another router outside of the range of 23.1.2.128 - 23.1.2.159. do I need to recalculate the best summary or just advertise that new nework?

best regards,

Alcides

[Keith6783]

@MadProd209

If it is just one additional network, outside the range, just letting the route be advertised is our only real option (with only a single additional route). If we had many new routes that were close to each other, we could summarize those new routes into a matching summary.

With R9, because he is a stub, we could really just use a default static route on R9, and we would be done as well.

Great question, and thanks for posting!

Keith

[Keith6783]

@brooklynzoo81-

Thanks for the feedback. It is always appreciated.

Keith

[Keith6783]

@snedie69er-

For the CCIE, list out all the topics, rank your current knowledge and skills in each area from 1 to 5 (5 being expert level). Schedule time daily/weekly, and use that time to study, and practice, moving your skills closer and closer to the 5 zone.

Best wishes, Keith.

[brooklynzoo81]

Great video.

[snedie69er]

Hey Kieth, yet another great video: Just in time to as I'm covering summarization right now.

I'm just getting stuck into CCNP ROUTE, do you have any tips for studying that you yourself have used to get to where you are now as a CCIE?

Thanks, and keep the video's coming :)

[Keith6783]

@Flienlow-

Thanks for the feedback.  It is appreciated.

Best wishes,

Keith

[Flienlow]

Excellent Video Keith!