Route Summarization

How would you know if route summarization is used if you were given the subnet aka 192.168.156.0/22? maybe I'm drawing a blank here...

Logically I look at this and it's a class c and by default class C only has 254 usable IPs is that the only way to figure this puzzle out?

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Ltat42a

Use the "show ip route" command....it should show what routes are within that subnet.

fluk3d

Thanks.. But what if you wanted to work this out via pen and paper no equipment used

DANMOH009

Have you been given a question or a scenario?

Im sure i'll get confirmation of this but i was led to believe that 192.168.156.0/22 is just like any other IP and Subnet, a Subnet with 1022 Hosts 36 Subnets. Just because its /22 doesnt really mean that it is a summary address.

fluk3d

DANMOH009 wrote: »

Have you been given a question or a scenario?

Im sure i'll get confirmation of this but i was led to believe that 192.168.156.0/22 is just like any other IP and Subnet, a Subnet with 1022 Hosts 36 Subnets. Just because its /22 doesnt really mean that it is a summary address.

No just curious using the techexams subnet calculator whenever I input that information I can see that it's a supernet addresses so I want to know the logic behind how it determined it was a supernet and not a regular subnet

CodeBlox

Supernets can have a shorter prefix length than the default classful network masks. If you look in the routing table at routes that have been summarized however (NOT supernets), they'd show with just the summary and anything that falls in that range uses that route.

fluk3d

CodeBlox wrote: »

Supernets can have a shorter prefix length than the default classful network masks. If you look in the routing table at routes that have been summarized however (NOT supernets), they'd show with just the summary and anything that falls in that range uses that route.

Definitly however; this is what I'm talking about how did this utility determine this was a supernetted address; what is the math behind it ?

supernet.JPG

networker050184

No math involved. As CodeBlox pointed out if the mask is shorter than the default classfull mask then its a supernet.

mella060

fluk3d wrote: »

Thanks.. But what if you wanted to work this out via pen and paper no equipment used

What is the range of 192.168.156.0/22 ?

From my understanding, the range would be 192.168.156.1 - 192.168.159.255

Next network is 192.168.160.0/22 and so on. The number just increments/goes up by 4 in the 3rd octet.

Looking at the summary address, i would assume that this summary is for the class c networks...

192.168.156.0/24
192.168.157.0/24
192.168.158.0/24
192.168.159.0/24

Since all of those subnets fall in the range of the summary address.

zrockstar

To summarize with pen and paper, write out your subnets you want to summarize in binary. What ever the last common bit across all IPs is, draw a dividing line between that bit and the next. Everything to the left of the line = your summary IP address, and however many bits are common is your subnet mask.

Maybe this will help:

STEP ONE: WRITE IN BINARY

192.168.XOOXXXOO.0
192.168.XOOXXXOX.0
192.168.XOOXXXXO.0
192.198.XOOXXXXX.0

STEP TWO: DRAW A LINE

192.168.XOOXXX|OO.0
192.168.XOOXXX|OX.0
192.168.XOOXXX|XO.0
192.168.XOOXXX|XX.0
<<<<<KEEP>>>>|<<CONVERT TO ALL 0s>>

STEP THREE: CONVERT IP

192.168.156.0

STEP FOUR: COUNT SUBNET MASK BITS

192.168.XOOXXX

12345678.12345678.123456 = 22

SUMMARY IP = 192.168.156.0/22

zrockstar

Sorry. After reading the thread again, I realize you weren't asking how to summarize, but as previously stated, a supernet is just a mask that is less than the classful address. I'll leave my previous comment up in case it does help you or someone else understand it a little better.

fluk3d

Thanks that's what I was looking for the mask is "smaller" then it's default mask