Help with prefix-list, distribution-list and route-map

[Steph1963]

Hi Everybody,

Can somebody explain to me why the following prefix-list

ip prefix-list E permit 0.0.0.0/1 le 24

corresponds to any prefix in a Class A address space covering at least 256 address. I can understand the class A part because the first bit must be 0 but I cannot understand the address space covering at least 256. Why 256 and what does it really means?

Found these two question from TROUTE course and just cannot understand the answer

Which two tools can be used to match traffic that is controlled by a distribute list (Choose 2)

Question 1

a) access-list

b) prefix-list

c) route maps

d) match lists

The answer is a&c but I found the following command from http://www.cisco.com/en/US/docs/ios/12_2/iproute/command/reference/1rfeigrp.html#wp1030091

distribute-list {access-list-number | prefix prefix-list-name [gateway prefix-list-name]} in [interface-type interface-number]

Why does prefix-list is not a valid answer?

Question 2

Route maps cannot match network based on access lists and change the metric value and metric type during the redistribution process

a) True

b) False

The answer is a but I would like verify my understanding of route-maps. Does route-map can only change the metric value of EIGRP and OSPF? Does the metric type only applied to OSPF? Does this question refers to the capacity of chaning one of these two parameters or does it refers to the capacity of changing metric value and metric type at the same time?

Thanks for your help

Stéphane

[milan.kulik · Accepted solution]

Hi,

regarding

ip prefix-list E permit 0.0.0.0/1 le 24

The "address space covering at least 256" is based on the "le 24" option. It means: the prefix lenght must be less or equal to 24 bits.

Which means, the x.x.x.0/24 or bigger subnets are matching, i.e., the host part includes x.x.x.0 - x.x.x.255 = 256 adrresses at least.

I don't know what TROUTE course is but the Internet is full of free study materials with a lot of errors in the test parts.

As you found yourself, the correct answer to Q1 should ba a) and b).

And there might be a typo in Q2 where should be "can" instead of "cannot".

Otherwise the question is really confusing and should have been divided into three separate questions.

BR,

Milan

[ashok_boin · Accepted solution]

Hi,

The answer to Q1 is a,b & c as we can utilize distribute lists along with route-map as well.

Example:

http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/routmap.html#wp1027129

Regards...

-Ashok.