Administrative Distance (AD), which decides which route the router prefers when multiple routing sources exist.

 Administrative Distance (AD), which decides which route the router prefers when multiple routing sources exist.

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🥇 Route Priority (Cisco default)

When static, OSPF, and EIGRP are all present for the same destination, the router chooses based on lowest Administrative Distance (most trusted route source).

Routing Type	Protocol	Default AD	Priority
Static route	Manual	1	🥇 Highest (most preferred)
EIGRP (internal)	Dynamic	90	🥈
OSPF	Dynamic	110	🥉

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🧠 So who wins?

👉 Static route wins most of the time

Because:

• AD = 1 (lowest)
• Router trusts it the most

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⚠️ Important exception: “Floating Static Route”

If you configure static route with higher AD:

ip route 192.168.1.0 255.255.255.0 10.1.1.1 200

Then:

• OSPF (110) or EIGRP (90) will be preferred
• Static route is used only as backup

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🔄 Real decision flow inside router

When multiple routes exist:

1. Check Administrative Distance (AD)
2. Lower AD wins
3. If same AD → check metric (OSPF cost, EIGRP metric)
4. If same metric → load balancing (ECMP)

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📊 Example scenario

You have destination: 192.168.10.0/24

Router learns:

• Static route → AD 1
• EIGRP route → AD 90
• OSPF route → AD 110

Result:

👉 Router uses STATIC ROUTE

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🧠 Easy memory trick

• Static = Strongest trust (AD 1)
• EIGRP = Medium trust (90)
• OSPF = Lower trust (110)

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🔥 Interview answer

When static, OSPF, and EIGRP routes exist for the same destination, the router chooses the route with the lowest Administrative Distance. By default, static routes have AD 1, EIGRP internal routes have AD 90, and OSPF routes have AD 110. Therefore, static routes are preferred over dynamic routing protocols unless a floating static route is configured with a higher AD.