CCNP Questions (2) on BGP

papamichail · ‎05-03-2008

I read the CCNP BSCI Official Certification Guide and I believe that the book contains errata in 2 topics in BGP (actual book questions).

1. A route has an AS-Path of 7 25 19 69. What can you learn from reading this path?

a. The local AS is 7.

b. The origin AS is 69.

c. There is a loop

d. 7 is the origin

Although i believe that a) is correct, in the Answers section of the book b) appears as the right answer. Anyone can tell me why?

2. Consider the following route map. What will be the local-preference for 192.168.25.0/24?

access-list 39 permit 192.168.24.0 0.0.3.255

access-list 32 permit 192.168.26.0 0.0.0.255

route-map test permit 10

match ip address 39

match ip address 32

set ip local preference 150

route-map test permit 20

match ip address 39 32

set ip local preference 200

a.0

b.100

c.150

d.200

Again I believe that the correct answer is d) but in the Answers section of the book c) appears as the right answer. Anyone can tell me why?

Istvan_Rabai · ‎05-03-2008

Hi Georgios,

For question 1:

b. is the right answer. As BGP routers pass routes from AS to AS they append their AS number to the AS path attribute.

So the first AS where the route originated was AS 69. The last AS the route left was AS 7 when it arrived to the local AS.

For question 2.

The right answer is d. because of the following:

Obviously, 192.168.25.0/24 will match only acl 39.

In the route map this acl appears twice:

Route-map entry 10:

is true if "match ip address 39" AND "match ip address 32" is true.

Route-map entry 20:

is true if "match ip address 39" OR "match ip address 32" is true.

This is why Route-map entry 20 will be true and its "set ip local preference 200" command will be executed.

The rule here is:

route-map test permit 10

match x

match y ----------- match x AND match y AND match z

match z

route-map test permit 20

match x y z ------ match x OR match y OR match z

Cheers:

Istvan