RE: Prefix-list Narbiks free workbook question

Hans,

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of Hans Eriksson
Sent: Thursday, October 14, 2010 5:20 AM
To: ccielab_at_groupstudy.com
Subject: Prefix-list Narbiks free workbook question

>Task 24
>Configure R2 such that it ONLY allows the following two prefixes in its routing table:
>10.4.4.32 /27 and 10.4.5.64 /26
>
>10.0.0.0/8 is variably subnetted, 11 subnets, 7 masks R 10.4.2.8/29 [120/1] via 10.1.12.1, 00:00:04, FastEthernet0/0 R 10.4.1.4/30 [120/1] via 10.1.12.1, 00:00:04, FastEthernet0/0 R 10.7.1.0/24 [120/1] via 10.1.12.1, 00:00:04, >FastEthernet0/0 R 10.7.0.0/24 [120/1] via 10.1.12.1, 00:00:04, FastEthernet0/0 R 10.7.3.0/24 [120/1] via 10.1.12.1, 00:00:04, FastEthernet0/0 R 10.7.2.0/24 [120/1] via 10.1.12.1, 00:00:04, FastEthernet0/0 R 10.4.3.16/28 [120/1] via >10.1.12.1, 00:00:04, FastEthernet0/0 R 10.4.4.32/27 [120/1] via 10.1.12.1, 00:00:04, FastEthernet0/0 R 10.4.5.64/26 [120/1] via 10.1.12.1, 00:00:04, FastEthernet0/0 R 10.4.6.128/25 [120/1] via 10.1.12.1, 00:00:04, FastEthernet0/0
>
>8.8.00000100.00100000
>8.8.00000101.01000000
>
>Ip prefix-list <name> permit seq 10 10.4.4.0/23 ge 24 le 27 the part 10.4.4.0/23 = OK but ge 24 le 27 are not so clear.

If you take another look, the more correct answer is in red. Not sure why the answer key lists ge 24 le 27, when ge 26 le 27 does the trick. So you're okay on the /23 to include the prefix 10.4.4.0, from there you want all prefixes with a subnet length of 26 or greater and 27 or less, effectively giving you 10.4.4.0/27 or 10.4.4.0/26 all the way till 10.4.5.224/27 or 10.4.5.192/26. Make sense?

>Task 26 also a problem.
>
>Coud someone help me understand.

10.4.0.0/22 and 10.4.4.0/22 cover the first 3 octects that show up in the routing table, from 0 - 7 for the 3rd octect. I guess the objective is to use two lines and be as specific as possible. I think the following is a bit more specific:

ip prefix-list TST permit 10.4.0.0/22 ge 28 le 30
ip prefix-list TST permit 10.4.4.0/22 ge 25 le 27

-ryan

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Received on Thu Oct 14 2010 - 12:52:48 ART