Administrative Distance Chart – Explained with CLI, Lab, Use Cases & FAQs [CCNP ENTERPRISE]

If you’re diving into routing protocols or just wrapping your head around how your router picks the “best” path, you must understand the concept of Administrative Distance (AD).

Think of AD like trust levels among friends. You’ve got friends (routing protocols) like OSPF, EIGRP, RIP, and static routes — but whom do you trust the most when two or more give you different answers for the same destination? That’s what AD does — it helps the router decide which route to believe.

Let’s break it all down into bite-sized learning below

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Theory in Brief: What is Administrative Distance?

Administrative Distance is a numerical value (0 to 255) that defines the trustworthiness of a routing source. Lower the number, higher the trust.

• Imagine your router receives the same route from OSPF and from RIP.
• It has to decide which one to install in the routing table.
• Here’s where AD comes into play.
• OSPF has an AD of 110, while RIP has 120. So, OSPF wins, and that’s the route the router adds.

In short, AD is Cisco’s way of choosing the most believable path.

AD only matters when multiple routing protocols or route sources advertise the same destination network. It’s not involved in metric-based decisions inside a protocol — that comes after AD has picked the protocol.

You can even manually adjust AD if needed — though do it carefully, especially in production!

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Administrative Distance (Default Values)

Routing Source	Administrative Distance
Connected Interface	0
Static Route	1
eBGP	20
EIGRP (internal)	90
OSPF	110
IS-IS	115
RIP	120
EIGRP (external)	170
iBGP	200
Unknown/Untrusted	255 (Never used)

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Pros and Cons of Using AD

Pros	Cons
Simple way to choose preferred routing source	Can be misconfigured, causing incorrect route selection
Helps in hybrid routing environments (OSPF + BGP etc.)	Doesn’t look at route metric or bandwidth
Easily adjustable for custom routing behavior	AD values are Cisco-specific (may vary in other vendors)

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Essential CLI Commands

Purpose	Command	Description
View routing table	show ip route	Displays active routes and their AD
View EIGRP routes only	show ip route eigrp	Filters routes learned via EIGRP
View OSPF routes only	show ip route ospf	Filters OSPF-specific routes
Check static routes	`show running-config	include ip route`
Modify static route AD	ip route x.x.x.x y.y.y.y z.z.z.z AD	Adds a static route with custom AD
Debug routing table decisions	debug ip routing	Shows real-time changes in routing decisions

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Real-World Use Case

Scenario	Description
Dual routing scenario – OSPF and EIGRP used	In a migration project from EIGRP to OSPF, both protocols advertise routes.
Requirement	Prefer OSPF but keep EIGRP as backup
Solution	Adjust EIGRP’s AD from 90 → 120 to prefer OSPF
Command Used	distance 120 under EIGRP process
Result	Router prefers OSPF routes unless OSPF is down

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Small EVE-NG Lab: Administrative Distance in Action

Topology Diagram

Goal:
All routers advertise 192.168.10.0/24. R3 learns it via both OSPF and EIGRP. We’ll observe which path gets installed.

Configurations

R1 – Advertises 192.168.10.0 via OSPF

interface loopback0
 ip address 192.168.10.1 255.255.255.0

router ospf 1
 network 192.168.10.0 0.0.0.255 area 0

R2 – Connects both OSPF and EIGRP

Editrouter ospf 1
 network x.x.x.x area 0

router eigrp 100
 network x.x.x.x

R3 – Learns via both protocols

router ospf 1
 network x.x.x.x area 0

router eigrp 100
 network x.x.x.x

Verification on R3

show ip route 192.168.10.0

• Initially, EIGRP route will win (AD 90 vs OSPF 110).
• Adjust OSPF preference:

router eigrp 100
 distance 130

• Now, OSPF route is preferred.

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Troubleshooting Tips

Issue	Command/Approach	Description
Wrong route chosen	show ip route	Check which AD value won
AD incorrectly set	`show run	section router`
Static route not installing	debug ip routing	See real-time routing decisions
Route flapping between sources	Stabilize AD manually	Adjust AD to avoid route flapping
BGP route not preferred	Remember iBGP has AD 200	Consider using route-map or weight instead

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Most common FAQs

1. What is Administrative Distance (AD) in networking?

Answer:
Administrative Distance is a numerical value that indicates the trustworthiness of a route’s source.
The lower the value, the more preferred the route.

For example:

• AD 0 = Directly connected (most trusted)
• AD 1 = Static route (highly trusted)
• AD 110 = OSPF (less trusted than EIGRP)

Routers use AD to compare routes to the same destination learned from different protocols.

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2. Why is Administrative Distance important?

Answer:
AD helps the router decide between multiple routes to the same destination when they come from different sources.

Example:
If a route to 10.10.10.0/24 is available via both OSPF (AD 110) and EIGRP (AD 90), the router will choose EIGRP.

This prevents conflicts, loops, and routing instability in complex networks.

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3. What is the default Administrative Distance chart in Cisco IOS?

Answer:

Route Source	AD Value
Connected Interface	0
Static Route	1
eBGP	20
EIGRP (internal)	90
IGRP	100
OSPF	110
IS-IS	115
RIP	120
EIGRP (external)	170
iBGP	200
Unknown (untrusted)	255 (unusable)

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4. Can Administrative Distance be changed manually?

Answer:
Yes, you can manually adjust AD to influence route selection.

Example – lowering the AD of a static route:

ip route 192.168.1.0 255.255.255.0 10.1.1.1 5

This static route now has AD 5, making it more preferred than OSPF (110) or EIGRP (90).

Use this carefully to control backup vs. primary routes.

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5. What happens if two routes to the same destination have the same AD?

Answer:
If routes have:

• Same prefix
• Same AD

The router chooses the one with the lowest metric (e.g., cost in OSPF, composite metric in EIGRP).

If metrics are equal, and protocol allows, the router may install multiple equal-cost routes (ECMP – Equal Cost Multi-Path).

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6. How do I view Administrative Distance in the CLI?

Answer:
Use the command:

show ip route

Example output:

D    10.10.10.0/24 [90/2172416] via 192.168.1.1
O    10.10.10.0/24 [110/2] via 192.168.2.1

• First number in brackets = AD
• Second number = protocol metric

Here, EIGRP (AD 90) wins over OSPF (AD 110).

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7. What’s the difference between Administrative Distance and Routing Metric?

Answer:

Feature	Administrative Distance	Metric
Purpose	Choose between routing sources	Choose best path within a protocol
Set by	Vendor (modifiable)	Protocol algorithm
Examples	OSPF = 110, EIGRP = 90	OSPF cost, EIGRP composite metric

AD comes first, then metric is considered.

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8. Can iBGP ever be preferred over OSPF or EIGRP?

Answer:
By default, no — iBGP has an AD of 200, which is less preferred than OSPF (110) or EIGRP (90).

However, you can manually manipulate AD of OSPF or static routes to influence behavior, though it’s not a common practice unless part of a specific design (like backdoor route management).

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9. What is a real-world use case of modifying Administrative Distance?

Answer:
Scenario:
You want to use a static route as a backup to a dynamic EIGRP route.

Solution:
Set the static route’s AD higher than EIGRP (90) but lower than OSPF (110):

ip route 192.168.2.0 255.255.255.0 10.1.1.2 100

This static route becomes the fallback if EIGRP fails — it stays inactive until needed.

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10. Can two routes with different masks (prefix lengths) have different ADs?

Answer:
Yes, but prefix length takes priority before AD is considered.

For example:

• Route A: 10.10.0.0/16 via OSPF (AD 110)
• Route B: 10.10.10.0/24 via RIP (AD 120)

For a packet going to 10.10.10.5, the router chooses the /24 RIP route — because it’s a longer match, regardless of higher AD.

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YouTube Video: Administrative Distance Explained with Lab Demo

Watch the Complete CCNP Enterprise: Administrative Distance Chart – Explained with CLI, Lab, Use Cases & FAQs Lab Demo & Explanation on our channel:

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Final Note

Understanding how to differentiate and implementAdministrative Distance Chart – Explained with CLI, Lab, Use Cases & FAQs is critical for anyone pursuing CCNP Enterprise (ENCOR) certification or working in enterprise network roles. Use this guide in your practice labs, real-world projects, and interviews to show a solid grasp of architectural planning and CLI-level configuration skills.

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