Solved

understanding Prefix-List

Posted on 2013-01-05
12
620 Views
Last Modified: 2013-01-15
I am trying to understand he usage of Prefix-List , but it seems like they are abit complex.
for instance:

1***what is this saying:
ip prefix-list test seq 12 permit 192.168.1.0/16 ge 24 le 24
is it permitting 1902.168.0.0 all the way 192.168.1.0 ?

2***what is this saying:
ip prefix-list test seq 12 permit 192.168.1.0/16 le 32
is it permitting anything that starts with 192.168.X.X all the way 192.18.254.254 ?

3*** what about this, doe s it need "le" or "ge"
0.0.0.0/0

4*** what about these:
0.0.0.0/0 le 32
0.0.0.0/32


Thank you
0
Comment
Question by:jskfan
12 Comments
 
LVL 17

Assisted Solution

by:lruiz52
lruiz52 earned 166 total points
ID: 38747486
0
 

Author Comment

by:jskfan
ID: 38758305
Can you please check my post above and tell me if I am understanding it the right way or wrong way ?
thanks
0
 
LVL 32

Assisted Solution

by:harbor235
harbor235 earned 167 total points
ID: 38767069
We are dealing with prefixes or subnets only here, do you understand subnets?

1***what is this saying:
ip prefix-list test seq 12 permit 192.168.1.0/16 ge 24 le 24
is it permitting 1902.168.0.0 all the way 192.168.1.0 ?

is this case of prefix lists 1*** means match all prefixes within the 192.168.1.0/24 networks a) greater an than or equal to 24 bits and b) less than or equal to 24 bits
Fancy way of stating match 192.168.1.0/24  Remember 192.168.1.0/24 is a subnet, all possible networks that can be subnetted by this parent block is in play, so 192.168.1.0/25, 192.168.1.128/25, and so on, get it?

2***what is this saying:
ip prefix-list test seq 12 permit 192.168.1.0/16 le 32
is it permitting anything that starts with 192.168.X.X all the way 192.18.254.254 ?

means match all prefixes within the 192.168.1.0/16 networks less than or equal to 32 bits,
so it means all possible subnets than can be subnetted from 192.168.1.0/16.


3*** what about this, doe s it need "le" or "ge"
0.0.0.0/0

with subnets this is sometimes used to mean all subnets when used with le 32
0.0.0.0/0 is a wildcard.

4*** what about these:
0.0.0.0/0 le 32
0.0.0.0/32

0.0.0.0/32 is an exact match meaning literally network 0.0.0.0 255.255.255.255 you see?

the important point here is that prefix lists deal with parent blocks and possible subnets that can be derived from that parent block.

harbor235 ;}
0
PRTG Network Monitor: Intuitive Network Monitoring

Network Monitoring is essential to ensure that computer systems and network devices are running. Use PRTG to monitor LANs, servers, websites, applications and devices, bandwidth, virtual environments, remote systems, IoT, and many more. PRTG is easy to set up & use.

 
LVL 17

Expert Comment

by:pergr
ID: 38767290
It is important to note that the prefix-list is use for matching prefixes (routes) and not individual IP addresses.
0
 

Author Comment

by:jskfan
ID: 38773427
sorry I did not get it
ip prefix-list test seq 12 permit 192.168.1.0/16 ge 24 le 24
so /16 is meaningless since it will pass only subnets with 24 bits ?

I see you mention 25 bits .... I did not get get it...
since the condition says greater or equal 24 and less or equal 24...which means to me just 24
0
 
LVL 17

Accepted Solution

by:
pergr earned 167 total points
ID: 38773433
The prefix that matches must have the exact subnet mask /24, and the prefix needs to be within 192.168.1.0/16 - which is the same as 192.168.0.0/16.

That would mean all 192.168.x.y/24 .
0
 

Author Comment

by:jskfan
ID: 38773515
I initially understood:
it will take : 192.168.1.0 to 192.168.254.0

Until I saw this, I extracted this from the pdf link given to me above:

ip prefix-list mylist seq 10 permit 172.16.0.0/16 ge 24 le 26
This will take the entire class B network 172.16.0.0 (172.16.0.0/16) and
pass only subnets with a /24, /25 or /26 mask (ge 24 le 26). So the exact
network 172.16.0.0/16 would actually fail the list because it does not have
a mask of /24, /25 or /26.
0
 

Author Comment

by:jskfan
ID: 38773516
very complex, hard to understand it..
0
 
LVL 17

Expert Comment

by:pergr
ID: 38773519
Correct.
0
 

Author Closing Comment

by:jskfan
ID: 38777365
Thank you Guys!
0

Featured Post

PRTG Network Monitor: Intuitive Network Monitoring

Network Monitoring is essential to ensure that computer systems and network devices are running. Use PRTG to monitor LANs, servers, websites, applications and devices, bandwidth, virtual environments, remote systems, IoT, and many more. PRTG is easy to set up & use.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
Telepresence on backup 3 33
fabric 1 33
new cisco 3750 switch setup 2 31
Unmanaged Switches for Optimized Network Speeds 7 51
Outsource Your Fax Infrastructure to the Cloud (And come out looking like an IT Hero!) Relative to the many demands on today’s IT teams, spending capital, time and resources to maintain physical fax servers and infrastructure is not a high priority.
Shadow IT is coming out of the shadows as more businesses are choosing cloud-based applications. It is now a multi-cloud world for most organizations. Simultaneously, most businesses have yet to consolidate with one cloud provider or define an offic…
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
Get a first impression of how PRTG looks and learn how it works.   This video is a short introduction to PRTG, as an initial overview or as a quick start for new PRTG users.

830 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question