Exam 300-410 topic 1 question 461 discussion

Inbound is correct for sure. Only answer "A" uses correct neighbor + direction. neighbor 192.168.2.2 route-map AS in Probably this explains, why they want to prepend AS 200 (remote AS number): https://blog.ipspace.net/2009/03/as-path-prepending-technical-details.html Inbound AS-Path Prepending ... to add an extra copy of the REMOTE AS number to inbound updates received from (neighbor)

Inbound, as the CE we presumably cannot touch the ISP and so have to manipulate inbound.

C as as-path prepend will only work outbound as it is a transitive attribute so it will be sent to the neighbor via BGP update message. Option A would be the answer is local preference is used.

If you select IN for orientarion, the AS Prepend is input during adj-rib-in, so, when these routes coming in lock-rib, this will loose preference, because ISP1 have best AS_Path. Realy these guys are aproved in enarsi??? lol

ANSWER IS: C A is very wrong the question is asking to influence the external route (the traffic coming from both ISPs), Additionally AS-Prepending used to influence traffic coming from outside. Note: if we want to influence the inbound traffic (Traffic going from within our AS to the ISPs) we will use either the weight or -the preferred method- Local preference.

A is corerct

For make the correct configuration you need to use or local preference or weight and then as-prepend. The first step if you have more routers inside AS 65500 is to put the local preference in inbound BEACAUSE REMEMBER THAT ==> LP is only in OUR AS, this mean that put LP in outbound direction to an another AS is useless. So inbound all the routers that you have in our AS will prefer to go through that path. Is not over yet! After that we got the LP we need to have symmetric routing here if we want to use only one path, so we need to advertise more times our own ASN via an as-prepend to ISP2, and you are asking yourself why?

Prepending is applied outbound. You want to make the backup path to appear as the longer path by advertising additional AS on this path and that is done outbound.

Answer is A

A is wrong because you have to apply the route-map to the outbound direction, Google " BGP deep Dive" and watch Kevin Wallace

Something wrong with this question. The original route map config is the same as answer A, save for the different AS. And both works without issues

When prepending an AS to a AS-PATH, you need to either prepend your own AS or the neighbor AS. Any other AS may cause problems. For this question, because we want to influence outbound traffic, we need to prepend received prefixes. The answer that fulfill both conditions is answer A.

for me option corerct is "C". I need out Prepending wit 200 200

The original configuration (set as-path prepend 111) did not influence the path-selection at all. Plus, none of the routes disappeared. The question seems to be incorrect.

Prepending as-number 111 inbound worked. It needs to be added two times, though (111 111). CE#sh run | sec route-map neighbor 192.168.2.2 route-map AS in route-map AS permit 10 set as-path prepend 111 111 CE#

Sorry, did not wait enough. Now it's OK. Using as-path prepend 111 111. Result: CE is choosing ISP1 as primary. CE#sh ip bgp BGP table version is 3, local router ID is 192.168.2.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, x best-external, a additional-path, c RIB-compressed, t secondary path, Origin codes: i - IGP, e - EGP, ? - incomplete RPKI validation codes: V valid, I invalid, N Not found Network Next Hop Metric LocPrf Weight Path * 1.1.1.1/32 192.168.2.2 0 111 111 200 100 i *> 192.168.1.1 0 0 100 i * 2.2.2.2/32 192.168.2.2 0 0 111 111 200 i *> 192.168.1.1 0 100 200 i CE#

The issue came after prepending AS 111 two times: CE#sh ip bgp BGP table version is 1, local router ID is 192.168.2.1 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, x best-external, a additional-path, c RIB-compressed, t secondary path, Origin codes: i - IGP, e - EGP, ? - incomplete RPKI validation codes: V valid, I invalid, N Not found Network Next Hop Metric LocPrf Weight Path * 1.1.1.1/32 192.168.1.1 0 0 100 i * 192.168.2.2 0 111 111 200 100 i * 2.2.2.2/32 192.168.1.1 0 100 200 i * 192.168.2.2 0 0 111 111 200 i CE#