Which source of routing information is preferred by default?
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A. B. C. D.A
By default, when Junos is evaluating routing information from multiple sources, it prefers the route learned from the source with the lowest administrative distance. Administrative distance is a measure of the trustworthiness of a routing protocol or source of routing information, and it is a value assigned by the system. The lower the administrative distance, the more trustworthy the protocol or source.
Here is the administrative distance for the routing protocols mentioned in the question:
A. OSPF internal - 10 B. OSPF external - 150 C. IS-IS Level 1 - 15 D. IS-IS Level 2 - 20
Therefore, OSPF internal (option A) has the lowest administrative distance of 10, and thus, it is preferred over OSPF external (option B), IS-IS Level 1 (option C), and IS-IS Level 2 (option D) by default.
It's important to note that the default preference can be changed using routing policy or by modifying the administrative distance values. Additionally, there may be other factors that come into play when evaluating routes, such as the metric or cost of the route.