# How to configure Prefix-List on Cisco Router
**URL:** https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944
**Category:** Lessons Discussion
**Created:** [December 24, 2016, 6:18pm UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944 "2016-12-24T18:18:27Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@ReneMolenaar](https://forum.networklessons.com/u/ReneMolenaar)
#### Post date: [December 24, 2016, 6:18pm UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944/1 "2016-12-24T18:18:27Z")
This topic is to discuss the following lesson:
> **[How to configure Prefix-List on Cisco Router](https://networklessons.com/eigrp/how-to-configure-prefix-list-on-cisco-router)**
>
> Prefix-lists are useful to filter prefixes by using the LE or GE operators. In this lesson, you learn how prefixes work.
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### Author:  [@system](https://forum.networklessons.com/u/system)
#### Post date: [October 16, 2013, 1:43pm UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944/2 "2013-10-16T13:43:59Z")
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…”
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### Author:  [@ReneMolenaar](https://forum.networklessons.com/u/ReneMolenaar)
#### Post date: [October 23, 2013, 8:56am UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944/3 "2013-10-23T08:56:06Z")
Hi Towdie,
You are totally right, just fixed this typo. Thanks for pointing it out!
Rene
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### Author:  [@system](https://forum.networklessons.com/u/system)
#### Post date: [January 22, 2014, 12:28pm UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944/4 "2014-01-22T12:28:00Z")
Rene i really like the way you explain.Thank you so much…
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### Author:  [@ReneMolenaar](https://forum.networklessons.com/u/ReneMolenaar)
#### Post date: [January 23, 2014, 9:05pm UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944/5 "2014-01-23T21:05:08Z")
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.
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### Author:  [@system](https://forum.networklessons.com/u/system)
#### Post date: [August 6, 2014, 5:07am UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944/6 "2014-08-06T05:07:49Z")
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..?
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### Author:  [@ReneMolenaar](https://forum.networklessons.com/u/ReneMolenaar)
#### Post date: [August 6, 2014, 9:04am UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944/7 "2014-08-06T09:04:10Z")
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
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### Author:  [@system](https://forum.networklessons.com/u/system)
#### Post date: [October 6, 2014, 8:23pm UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944/8 "2014-10-06T20:23:04Z")
Thanks for this explanation. It is really clear like the rest of all the subjects you covered.
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### Author:  [@system](https://forum.networklessons.com/u/system)
#### Post date: [October 6, 2014, 9:06pm UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944/9 "2014-10-06T21:06:50Z")
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
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### Author:  [@Openlearner](https://forum.networklessons.com/u/Openlearner)
#### Post date: [December 23, 2014, 12:16am UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944/10 "2014-12-23T00:16:56Z")
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
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### Author:  [@ReneMolenaar](https://forum.networklessons.com/u/ReneMolenaar)
#### Post date: [December 24, 2014, 10:14am UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944/11 "2014-12-24T10:14:53Z")
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:
> **[RIP Reliable Default Route with IP SLA](https://networklessons.com/rip/rip-reliable-default-route-with-ip-sla)**
>
> RIP can be configured to use IP SLA for Default Routes...but there is a trick to it!
> **[How to configure Policy Based Routing](https://networklessons.com/ip-routing/how-to-configure-policy-based-routing)**
>
> Policy based routing can be used to overrule your routing table and change the next hop IP address for traffic meeting certain requirements.
> **[How to configure Route Tagging](https://networklessons.com/ip-routing/how-to-configure-route-tagging)**
>
> Route tagging is used to ensure that you don't redistribute information from Routing Protcol A into B and back into A.
> **[BGP Route Refresh Capability](https://networklessons.com/bgp/bgp-route-refresh-capability)**
>
> This lesson explains the BGP Route Refresh Capability on Cisco IOS routers.
> **[BGP Local Preference Attribute](https://networklessons.com/bgp/how-to-configure-bgp-local-preference-attribute)**
>
> BGP Attribute Local Preference is used to change the exit path for an AS. In this lesson, you will learn how to configure local preference.
> **[BGP AS Path Filter Example](https://networklessons.com/bgp/bgp-as-path-filter-example)**
>
> This lesson explains how to use regular expressions and to create AS PATH access-list filters on Cisco IOS Routers.
> **[BGP Prevent Transit AS](https://networklessons.com/bgp/bgp-prevent-transit-as)**
>
> This lesson explains four configuration methods to prevent an autonomous system (AS) from becoming a transit AS.
> **[How to configure BGP MED Attribute](https://networklessons.com/bgp/how-to-configure-bgp-med-attribute)**
>
> BGP MED (Metric) is one of the BGP attributes and tells another AS how to enter your AS. I'll show you how to configure it on Cisco routers.
Rene
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### Author:  [@niiodaie](https://forum.networklessons.com/u/niiodaie)
#### Post date: [April 22, 2015, 11:08pm UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944/12 "2015-04-22T23:08:12Z")
Rene,
Do you have any video on subnetting ?
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### Author:  [@ReneMolenaar](https://forum.networklessons.com/u/ReneMolenaar)
#### Post date: [April 26, 2015, 4:39pm UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944/13 "2015-04-26T16:39:34Z")
Hi Jude,
All subnetting material can be found here:
[https://networklessons.com/subnetting-lessons/](https://networklessons.com/subnetting-lessons/)
Rene
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### Author:  [@johnfrades](https://forum.networklessons.com/u/johnfrades)
#### Post date: [July 30, 2015, 11:45am UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944/14 "2015-07-30T11:45:28Z")
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” ?
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### Author:  [@ReneMolenaar](https://forum.networklessons.com/u/ReneMolenaar)
#### Post date: [July 30, 2015, 8:47pm UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944/15 "2015-07-30T20:47:25Z")
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
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### Author:  [@johnfrades](https://forum.networklessons.com/u/johnfrades)
#### Post date: [August 2, 2015, 9:52am UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944/16 "2015-08-02T09:52:03Z")
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?
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### Author:  [@ReneMolenaar](https://forum.networklessons.com/u/ReneMolenaar)
#### Post date: [August 3, 2015, 8:41pm UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944/17 "2015-08-03T20:41:58Z")
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
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### Author:  [@hussien.samer](https://forum.networklessons.com/u/hussien.samer)
#### Post date: [September 27, 2015, 9:00pm UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944/18 "2015-09-27T21:00:43Z")
Hi Rene,
What is the benefit of using seq number in Prefix-List ?
Thanks.
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### Author:  [@mario\_ramales](https://forum.networklessons.com/u/mario_ramales)
#### Post date: [September 28, 2015, 7:43am UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944/19 "2015-09-28T07:43:07Z")
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
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### Author:  [@ReneMolenaar](https://forum.networklessons.com/u/ReneMolenaar)
#### Post date: [September 28, 2015, 11:33am UTC](https://forum.networklessons.com/t/how-to-configure-prefix-list-on-cisco-router/944/20 "2015-09-28T11:33:24Z")
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
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