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Network+ Exam

Route Selection

October 29, 2025

  • #network+

Route Selection

Determines whithc path a route should take.

Beliveablility of a route.

RIP is older so less beliveable vs OSPF.

AD administrative Distance - lower ad IS MORE TRUSTWORKTY or

directly connected 0 always belived.

static 1 - belive the admin

EIGRP 90 newist

OSPF 110 newer

RIP 120 oldest

External eigrp 170 older

UNKNOWN 255

for exam know the order not the numbers.

Metrics -

hop count, belivibility, realibility, bandwidth delay ,costs other metrics. it’s like golf rules lowest sore is the highest cost.

bandwidth 0 lowest cost

for route selection all are. etter.

Route Selection (N10-009)

Administrative Distance (AD)

  • Definition: How “trustworthy” a routing source is.
  • Rule: Lower AD = more believable.
  • If multiple routes exist to the same destination → the one with the lowest AD wins.

Common AD Values (memorize order, not numbers):

  • 0 – Directly Connected (always trusted most)
  • 1 – Static Route (set by admin)
  • 90 – EIGRP (internal)
  • 110 – OSPF
  • 120 – RIP (least believable common IGP)
  • 170 – EIGRP (external)
  • 255 – Unknown/invalid (never used)

👉 Exam Tip: Just know the priority order:

Direct > Static > EIGRP > OSPF > RIP > External EIGRP > Unknown

Metrics

  • Metrics determine the best path within a routing protocol.
  • Think of metrics as the score of the path → like golf: lowest = best.
  • Different protocols use different metrics:

| Protocol | Metric Used | | --- | --- | | RIP | Hop Count (max 15) | | OSPF | Cost (based on bandwidth) | | EIGRP | Composite (bandwidth, delay, reliability, load) | | IS-IS | Cost | | BGP | Path Vector (AS-path length + policies) |

✅ Must-Know for Exam

  • AD = trust between protocols. Metric = best path inside a protocol.
  • If a router knows a route from OSPF (AD 110) and RIP (AD 120), it chooses OSPF.
  • If it knows two OSPF routes, it chooses the one with the lowest cost metric.

⚡ Flashcards

  • Q: What is AD 0?

    A: Directly connected.

  • Q: Which has lower AD: OSPF or RIP?

    A: OSPF.

  • Q: Which routing protocol uses hop count?

    A: RIP.

  • Q: What does EIGRP use as a metric?

    A: Bandwidth + delay (composite).

  • Q: What happens at AD 255?

    A: Route is invalid/unusable.