Exam 300-410 topic 1 question 39 discussion

Answer D seems most logical. Question says that Branch B ONLY EVER uses MPLS B. That means you don't want the path through Branch A as an alternate. So A, B and C all prefer HQ routes, but they don't eliminate Branch A routes. D is the only answer which actually filters the route.

For me the site codification has a problem. The text with correct codification is below: Troubleshoot and ensure that branch B only ever uses the MPLS B network to reach HQ. Which action achieves this requirement? (A) Modify the weight of all HQ prefixes received at branch B from the MPLS B network to be higher than the weights used on the MPLS A network (B) Increase the local preference for all HQ prefixes received at branch B from the MPLS B network to be higher than the local preferences used on the MPLS A network (C) Introduce AS path prepending on the branch A MPLS B network connection so that any HQ advertisements from branch A toward the MPLS B network are prepended three times (D) Introduce an AS path filter on branch A routers so that only local prefixes are advertised into BGP

!RouterA/BranchA ip as-path access-list 1 permit ^$ ! router bgp 65000 address-family ipv4 unicast neighbor 1.1.1.1 filter-list 1 out The above config would prevent BranchA from becoming a transit AS by only advertising locally learned routes upstream to HQ. So according to HQs routing table, the only way to get to BranchB is through MPLSB.

D seems correct

it´s D

The provided answer is correct. For D, MPLS is working with iBGP. Don't know how to use AS_PATH filter.

as many users as said the only answer that can be the true one is D the other answers are just make the route less prefered, by the way we assume that the branch is using another ASN number, because if the ASN is the same the advertisement will be sent anyway because they are ibgp neighbors and when you receive and ibgp update the ASN number is not specified in the update (remember that if also Branch B will be an ibgp neighbor to configure RR in RB)

The only way to be shure that branch B do do not use Branch A as transit is jus filter Branch A to filter the annoumcent to HQ, So D is correct

Branch A with option D, is not transit AS for the other two AS, thus BRANCH B always goes to MPLS B to HQ

To me B is not correct because in this case we're using a MPLS network and the weight variable only exits on cisco equipment and is for local use, and D option seemed most appropiate.

After reading the questions many times, D is seem to be the correct one. Other answers just make the route via MPLS B is prefer to MPLS A. If the link is down, B will go to A to HQ. So D is the correct one

B is wrong. route from branch A goes to MPLS B. D is correct.

B is the correct one

A - the path through branch A is worsened by the lengthening of AS-path, keeping the alternative. Condition "only ever uses" is not met. B - when the route with the best WEIGHT disappears from the table, traffic will flow through branch A. Condition "only ever uses" is not met. C - the path through branch A is still preserved, the path through MPLS B is being improved by LP. D(correct answer) - office A advertises up and to the right of the picture only its own routes, branch B does not have an alternative route to HQ, branch B ONLY EVER USES the MPLS B network to reach HQ. * - I assume that ׀' is B.

Alnet is correct with his explanation, D is correct it would seem

B seems to be the correct one According to Image, you should be routed via Branch A D is incorrect, if you Introduce an AS path filter on branch A routers so that only local prefixes are advertised into BGP, how the branch B will know the path via Branch A to the Network HQ?

B is the corect one.