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Which of the following MUST be implemented to share metrics between routing protocols within the same router?

Which of the following MUST be implemented to share metrics between routing protocols within the same router?

A.

Routing loop

B. Routing table

C. Route redistribution

D. Dynamic routes

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2 Comments on “Which of the following MUST be implemented to share metrics between routing protocols within the same router?

  1. klt316 says:

    The Q isn’t worded well at all, there is no such thing as “sharing metrics”. A routing table does not “share” metrics, it uses AD. However, a metric is a measure of best path WITHIN a routing protocol. RIP uses hop count as its metric, but OSPF uses cost. A routing table doesn’t use METRICS it actually uses Administrative Distance. AD is a value between 0-255, lower the better. So where METRIC is used WITHIN a routing protocol, AD is used in the ROUTING TABLE. So that answer is not correct. ROUTE REDISTRIBUTION, on the other hand, is used to exchange routing information between different protocols within the same router. Sounds like the Q, eh? If I want to share a ROUTE (not a metric) from one routing protocol to another on the same router, I must “redistribute” that route from one to another. That’s why “C” must be the correct answer.




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    1. klt316 says:

      After re-reading this, maybe I didn’t use the best wording… Metrics are used in a route table but only WITHIN a routing protocol. If there are multiple routing protocols, it doesn’t share those metrics between protocols, that’s what AD is for, to determine the best route BETWEEN DIFFERENT ROUTING PROTOCOLS. The Q asks what must be “implemented” to “share metrics” between [different] “routing protocols”. First, a routing table isn’t implemented, it’s always there. A “sh ip route” will show you the routing table, however basic. Even without a routing protocol configured, the “connected” interfaces will show up in the routing table to show destination routes thru those connected interfaces. Those basic routes thru “connected” interfaces are all given an AD of “0” meaning they are highest priority for given traffic. If a “static” route is implemented, the routing table will assign it an AD of “1” with the 2nd highest priority. If a dynamic routing protocol is implemented, the routing table will assign it an associated AD (EIGRP 90, OSPF 110, RIP 120, etc…). So a route table isn’t “implemented”, it’s just there. Also note that metrics of different routing protocols cannot be directly compared. Metrics are shared only WITHIN routing protocols, it is NOT the mechanism in use “BETWEEN” routing protocols. That’s the AD. For a particular route, the lowest AD is chosen first, if there is more than one route with the same AD, then the lowest METRIC is chosen. If a destination has the same AD and same METRIC, say two RIP routes (same AD) each 1 hop away (same metric), the route is load balanced. There is no “sharing” of metrics between routing protocols. So technically “ROUTING TABLE” cannot be a correct answer. The routing table does share metrics WITHIN a single routing protocol and it shares AD BETWEEN routing protocols. Does that satisfy the Q though? I think not. There is no such thing as “sharing metrics between routing protocols”. But you can INJECT a particular route from one routing protocol to another and adjust its metric, and for that “Route Redistribution” is used. Not exactly what the Q is asking either. Pick your poison for this practice Q, the actual test will be more definitive in its Q’s.




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