Exam JN0-664 topic 1 question 55 discussion

B (MED) is wrong, as by default, the MED attribute is only compared for routes received from the same neighbouring AS. The next feasible tiebreaker in the BGP route selection algorithm would be Router ID.

I'd use MED for this

D. IGP Metric. Why? Lowest IGP metric is evaluated after EBGP over IBGP and before shortest cluster ID List and Lowest Router ID.

For eBGP router ID would be the next tie break from the given options. IGP metric is not evaluated for eBGP path selection.

Doesn't make sense to change either router ID ot peer IP address to influence traffic flow "MED always compare" can be used in conjunction with MED value that could be altered by routemaps upon receiving the prefix, plus IGP metric is compared after MED, hence B

D is correct

B. MED value Explanation: MED (Multi-Exit Discriminator): The MED attribute, also known as the metric, is used to influence the inbound traffic from external ASes. It is compared between routes learned from different ASes to determine the preferred route when multiple routes to the same destination are available. Although MED is primarily used for influencing traffic entering your AS, it is the next step in path selection if the local-preference, AS-path length, and origin codes are the same. Router ID: The router ID is not used in BGP route selection. It is more relevant for identifying BGP routers and for OSPF (Open Shortest Path First) routing. Peer IP Address: The peer IP address is not used in the BGP path selection process. It is used for identifying BGP peers but does not influence route preference. IGP Metric: The IGP metric is used in BGP path selection when comparing routes learned from the same AS, not from different ASes. Since your routes are from different ASes, the IGP metric will not influence the BGP decision in this scenario.

D: A path is considered a BGP equal-cost path (and is used for forwarding) if the BGP path selection process performs a tie-break after comparing the IGP cost to the next-hop. By default, all paths with the same neighboring AS, learned by a multipath-enabled BGP neighbor are considered in the multipath selection process.

D is correct because IGP metric is considered before Router-ID.

https://www.juniper.net/documentation/us/en/software/junos/vpn-l2/bgp/topics/concept/routing-protocols-address-representation.html

MED is ruled out as this is for entering traffic. for exit traffic next after MED is Lowest IGP Metric. so Answer D

D should be the correct answer: IGP Metric Step-6 of the path selection algorithm: Prefer path whose next-hop is resolved by IGP route with lowest IGP metric.

D: Should be IGP Metric https://networklessons.com/bgp/bgp-attributes-and-path-selection https://www.juniper.net/documentation/us/en/software/junos/vpn-l2/bgp/topics/concept/routing-protocols-address-representation.html

MED is used to influence inbound traffic so it's not the correct answer. In this case Router ID is the tie beaker.