Prefix-list question

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Sep 10th, 2010
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Hi expert,


How can I count the actual IP range of below prefix list


ip prefix-list abc seq 10 deny 10.100.64.0/18 ge 24
ip prefix-list abc seq 20 permit 10.100.0.0/16 ge 24
ip prefix-list abc seq 30 deny 10.100.0.0/14 ge 16
ip prefix-list abc seq 40 deny 10.104.0.0/13 ge 16
ip prefix-list abc seq 50 deny 10.112.0.0/13 ge 16
ip prefix-list abc seq 100 permit 0.0.0.0/0 le 32

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Federico Coto F... Fri, 09/10/2010 - 12:19
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Not sure what your question is.

You have a list of prefix lists each one with different instructions.

You want to know which IP ranges are matched by the permit statements? Please clarify.


Federico.

milan.kulik Sun, 09/12/2010 - 12:10
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Hi,


ip prefix-list abc seq 10 deny 10.100.64.0/18 ge 24 is matching any prefix within 10.100.64.0/18 (=10.100.64.0 - 10.100.127.255) but the prefix mask length must be greater or equal /24. Which means 10.100.66.0/24 is matched, but 10.100.66.0/23 is not, e.g.

The deny keyword is inverting the prefix acceptance logic though, i.e., the matching prefixes are being dropped by the router.


ip prefix-list abc seq 20 permit 10.100.0.0/16 ge 24 is matching any prefix within 10.100.0.0/16 (=10.100.0.0 - 10.100.255.255) but the prefix mask length must be greater or equal /24.


For

ip prefix-list abc seq 30 deny 10.100.0.0/14 ge 16
ip prefix-list abc seq 40 deny 10.104.0.0/13 ge 16

ip prefix-list abc seq 50 deny 10.112.0.0/13 ge 16

the logic is similar to the first line.


ip prefix-list abc seq 100 permit 0.0.0.0/0 le 32 is matching any prefix.

BR,

Milan

acbennyma Sun, 09/12/2010 - 20:38
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Hi ,


For ip prefix-list abc seq 10 deny 10.100.64.0/18 ge 24, is it means that


Within the IP range  10.100.64.0 - 10.100.127.255

if route is 10.100.64.0 /24, then is match and will be dropped

if route is 10.100.65.0/ 24, then is match and will be dropped

if route is 10.100.67.0/ 26, then is match and will be dropped

if route is 10.100.64.0/ 22, then is not match and will not dropped

if route is 10.100.72.0/ 22, then is not match and will not dropped

milan.kulik Sun, 09/12/2010 - 21:59
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Hi,


yes, correct.

This line does not match it.

The final dropping/accepting depends on the following prefix-list lines finally.


BR,

Milan

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