RIP Behavior — Receiving a Higher-Cost Path for an Existing Network Two directly connected routers run RIP. If a router receives an update that advertises a higher-cost (larger hop count) path to a destination that already exists in its routing table with a lower cost, what does RIP do?

Difficulty: Easy

Correct Answer: The update will be ignored and no further action will occur.

Explanation:


Introduction / Context:
RIP chooses routes based on minimum hop count. When multiple advertisements for the same prefix arrive, RIP keeps the lowest-hop path. Understanding how RIP treats worse paths helps explain stable behavior and reduces unnecessary churn.


Given Data / Assumptions:

  • RIP metric is hop count (lower is better).
  • An existing route with lower hop count already resides in the RIB.
  • A new update arrives with higher hop count.


Concept / Approach:
RIP installs the best path by hop count. If a newly received advertisement has a worse metric, the router ignores it for route selection. Only if the existing route becomes invalid (for example, times out) or a strictly better metric is learned will the RIB change. Triggered updates and holddown rules further stabilize choices by damping flaps.


Step-by-Step Solution:
Compare metrics: existing hop count vs. new hop count.If new hop count > existing hop count → mark as worse.RIP ignores worse paths; no RIB replacement occurs.Maintain current entry until a better or valid replacement appears.


Verification / Alternative check:
Observe with debug ip rip; you will see advertisements received but not installed if their metric is inferior to the current entry.


Why Other Options Are Wrong:

  • A: RIP does not keep multiple unequal-cost paths by default (RIPv2 supports equal-cost only).
  • C/D/E: Replacing, deleting, or forcing refresh for a worse path contradicts RIP selection rules.


Common Pitfalls:
Confusing “higher metric” with “fresher information”; freshness does not override worse metric in RIP.


Final Answer:
The update will be ignored and no further action will occur.

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