This topic is to discuss the following lesson:
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Hello,
in the lesson is:
What about 10.60.0.0 /19? It falls within the 10.0.0.0 /8 range but it is not permitted because it has a subnet mask of /23…our ge operator says it should be /20 or larger.
But the network has mask of /19 and not /23 so it should be “it has a subnet mask of /19…”
Hi Towdie,
You are totally right, just fixed this typo. Thanks for pointing it out!
Rene
Rene i really like the way you explain.Thank you so much…
Yes if you use a prefix-list without GE or LE then it’s just the prefix that you matched. For example, 172.16.1.0/24 is the same as 172.16.1.0 0.0.0.255 in an access-list.
Rene- Its crisp & Clear explanation…however can you help me to understand what prefixes are covered for 128.0.0.0/3 & 128.0.0.0/5…?
Hi Raghav,
First you need to figure out what /3 and /5 is, write down the subnet mask:
/3 = 224.0.0.0
/5 = 248.0.0.0
A quick way to find out how many subnets are covered is by taking the number 256 and subtracting the subnet mask:
256 - 224 = 32 subnets
256 - 248 = 8 subnets
So for /3 it looks like this:
Subnet #1: 0.0.0.0/3
Subnet #2: 32.0.0.0/3
Subnet #3: 64.0.0.0/3
Subnet #4: 96.0.0.0/3
Subnet #5: 128.0.0.0/3
Subnet #6: 160.0.0.0/3
And for /5:
Subnet #1: 0.0.0.0/3
Subnet #2: 8.0.0.0/3
Subnet #3: 16.0.0.0/3
Subnet #4: 24.0.0.0/3
Subnet #5: 32.0.0.0/3
Subnet #6: 40.0.0.0/3
Subnet #7: 48.0.0.0/3
Subnet #8: 56.0.0.0/3
Subnet #9: 64.0.0.0/3
Subnet #10: 72.0.0.0/3
Subnet #11: 80.0.0.0/3
Subnet #12: 88.0.0.0/3
Subnet #13: 96.0.0.0/3
Subnet #14: 104.0.0.0/3
Subnet #15: 112.0.0.0/3
Subnet #16: 120.0.0.0/3
Subnet #17: 128.0.0.0/3
Subnet #18: 136.0.0.0/3
Subnet #19: 144.0.0.0/3
Now you can see what prefixes are covered 
Rene
Thanks for this explanation. It is really clear like the rest of all the subjects you covered.
Just a quick typo, nothing serious…
10.1.0.0/16 is permitted because it’s in the 10.0.0.0/8 range and has a /16 subnet mask.
10.4.0.0/16 is permitted because it’s in the 10.0.0.0/8 range and has a /19 subnet mask.
Should be a /19 instead of /16
Hi Rene,
What about route-maps lesson?. It would have been nice to know how to apply it on different cases. Just a thought.
Love your lessons. I am stick to it
Hi Alfredo,
Hmm i’ll think about it. Route-maps can be used for many different things so not sure if 1 lesson with all these mixed topics would work. Here are some examples where we use route-maps:
Rene
Rene,
Do you have any video on subnetting ?
Hi Jude,
All subnetting material can be found here:
https://networklessons.com/subnetting-lessons/
Rene
Hi Rene, you explained it clearly, just one question. you said that
“ip prefix-list NAME permit 0.0.0.0/0 le 32” is like permitting all right?
is this the same with
“ip prefix-list NAME permit 0.0.0.0/0 ge 1” ?
Hi John,
Good question, it’s almost the same…the only difference is that 0.0.0.0/0 ge 1 won’t allow a default route.
The ge 1 means that the prefix should have a /1 or larger and a default route has a /0.
Rene
rene, if i have this prefix list “0.0.0.0/3 ge 24”, so anything on the 1st octet that is 0-31 is a valid range?
Hi John,
It means the first 3 bits of the 1st octet have to be a 0 and the subnet mask should be /24 or larger.
00000000 = 0
00011111 = 31
So yes, you are right
Rene
Hi Rene,
What is the benefit of using seq number in Prefix-List ?
Thanks.
I know this should be a clear answer, but for some reason I’m not understanding how 128.0.0.0/2 covers the whole Class B network range. If I write out 128 into decimal, it will be: I0000000. Now the mask says to match on the first two bits, so the only match would be the I0 ( I is matched and 0 is not matched?) which again equals to only the 128 network range. I would like a clear explanation on this if you may. Thanks
Hi Mario,
The first two bits have to be 10 so that means the following range is class B:
10000000 - 10111111
Or in decimal:
128 - 191
Rene