問題文
A dual-homed enterprise takes a feed from AS 64520 and another from AS 64530. For one prefix the path through AS 64520 carries a MED of 50 and the path through AS 64530 carries no MED at all. The two paths are equal in local preference, in AS path length and in origin code. The team expects the value 50 to lose against a path that carries nothing there. What does the device do with the configuration left at its defaults?
選択肢
- It weighs no MED here at all, because by default the metric is compared only between paths whose neighboring AS numbers agree, and the always-compare-med statement is what would make the device read the value 50 against an absent one that counts as zero.
- It reads the absent value as the largest one that fits the 32-bit field, so the path through AS 64530 loses on that step and the value 50 decides the prefix for as long as both paths stay in place.
- It compares the two values because MED is an end-to-end transitive attribute that every AS on the path is free to rewrite, so the path with the value 50 loses to the path that carries none of it.
- It adds the IGP cost of the next-hop address to the value 50 before the step is weighed, which is the standing behavior, so the path through AS 64530 wins with an effective metric of zero.