You're staring at a router console, studying for an exam, or maybe just trying to settle a weird argument at work. And the question pops up: which of the following has the least default administrative distance?
It sounds like one of those dry networking trivia questions. But here's the thing — it actually tells you a lot about how a router decides what to trust. And if you've ever wondered why your network picked one route over another, this is the knob that explains it And that's really what it comes down to. Surprisingly effective..
Administrative distance is one of those concepts that's simple in theory and quietly powerful in practice. Let's dig in.
What Is Administrative Distance
Administrative distance — sometimes called AD — is a number that routers use to rank the trustworthiness of a routing source. Lower is better. That's the whole game.
When a router learns about the same destination from more than one place, it has to choose. It doesn't pick based on speed or hop count first. It picks based on which source it's configured to trust most. That trust rating is the administrative distance That's the part that actually makes a difference. Less friction, more output..
And yeah — that's actually more nuanced than it sounds.
So if your router hears about 10.0.0.0/8 from both a static route and a routing protocol, the AD decides who wins before anything else gets considered.
Where The Number Comes From
Cisco and most vendors assign default AD values to common sources. Think about it: a directly connected network gets a tiny number. They're baked in. These aren't measured. A weird external protocol gets a big one.
The scale runs from 0 to 255. So zero means "don't even question it. " Two hundred fifty-five means "never use this, even if we're desperate.
Why It's Not A Metric
People mix this up constantly. AD is not the same as a metric. A metric is about cost — bandwidth, delay, hop count. Also, administrative distance is about source credibility. You compare AD only when the sources are different. If two routes come from the same protocol, AD doesn't enter the conversation Less friction, more output..
Why People Care About Default Administrative Distance
Why does this matter? Because most people skip it — and then their traffic goes the wrong way.
Imagine you set up a static route because you wanted a specific path. Then you turn on a dynamic routing protocol. Think about it: suddenly your static route gets ignored. Even so, not because it's wrong. Which means because the protocol had a lower default AD than you expected. Or vice versa.
In real networks, this shows up during migrations. Engineers panic. Here's the thing — you're moving from static configs to OSPF or EIGRP. So routes flap. Turns out the router just trusted the new protocol more But it adds up..
And if you're studying for CCNA or any networking cert, this question is basically a guaranteed test item. Knowing which source has the least default AD isn't academic. It's the difference between a stable network and a confusing one Worth knowing..
How It Works And The Default Values
Here's the short version: the least default administrative distance of any common source is 0, and it belongs to a directly connected network.
That's the answer to the question in the title. If you saw a list like "static route, OSPF, EIGRP, directly connected, RIP" — the directly connected network has the least default AD. Zero But it adds up..
But to actually understand it, you need the full picture.
The Common Default AD Table
Most Cisco-based gear uses these defaults:
- Directly connected interface: 0
- Static route (out an interface): 0 or 1 depending on config
- Static route (to next-hop IP): 1
- EIGRP summary route: 5
- External BGP: 20
- Internal EIGRP: 90
- IGRP: 100
- OSPF: 110
- IS-IS: 115
- RIP: 120
- External EIGRP: 170
- Internal BGP: 200
- Unknown or unreachable: 255
So when someone asks "which of the following has the least default administrative distance," and the options are normal routing sources, the directly connected network wins every time. If "static route" is phrased as directly out an interface, it can also be 0 — but connected is the classic textbook answer.
How The Router Decides
Step one: learn routes from all sources. Think about it: step two: for each destination, line up the contenders. Lowest AD wins. Step three: compare AD. Step four: if AD ties, then and only then do you look at the metric.
That order is everything. But a RIP route with a metric of 1 loses to an OSPF route with a metric of 1000, because 120 is higher than 110. The router doesn't care that RIP's path looks cheaper. OSPF is trusted more by default Worth keeping that in mind..
Can You Change It
Yep. You can manually set AD on static routes or per protocol. That's how engineers override defaults on purpose. But the question asks about default values. Out of the box, connected equals zero and nothing beats it.
Common Mistakes People Make With AD
Honestly, this is the part most guides get wrong. They treat AD like a score you want to minimize everywhere. It isn't.
One mistake: thinking the least AD always means the best path. It means the most trusted source. A directly connected route has AD 0 because the router sees the cable. No. That's not always the path you want for a remote subnet if you're doing weird tunneling — but by default, it wins That alone is useful..
Another mistake: confusing "default" with "current." Someone changes the static route AD to 250 in a lab, then answers a quiz wrong because they forgot the question said default. The defaults are fixed references. Your config might not match.
And here's a big one — people assume eBGP must be super trustworthy because it's external internet routing. Why? Which means its default AD is 20, which is low, sure. Plus, internal BGP is 200, which is shockingly high. But it's still higher than connected or static. Because iBGP routes are learned from inside your own AS and the router assumes you already have IGPs doing the heavy lifting Nothing fancy..
Look, I know it sounds simple — but it's easy to miss that AD is per-source, not per-route Not complicated — just consistent..
Practical Tips That Actually Work
If you're dealing with this in the real world, here's what helps Turns out it matters..
Don't blindly trust defaults during a protocol cutover. Your statics will stay. Still, if you're introducing OSPF into a static-heavy network, know that OSPF (110) will lose to static (1) by default. That might be what you want — or it might hide your OSPF routes entirely Worth knowing..
Use show ip route and look at the codes. Each route line shows the AD in brackets next to the metric. That's the fastest way to see who won and why Took long enough..
When you're answering the exam question, memorize the order: connected (0), static (1), eBGP (20), EIGRP internal (90), OSPF (110), RIP (120). The question "which has the least" almost always includes connected as an option. If it doesn't, static out an interface is your zero.
And in practice, if you need a route to absolutely win, set its AD lower than everything else. Just document it. Future you will thank you when the network behaves like it should.
FAQ
Which of the following has the least default administrative distance: connected, static, OSPF, or RIP? A directly connected network has the least, with a default AD of 0. Static is 1, OSPF is 110, RIP is 120.
Can administrative distance be negative? No. It ranges from 0 to 255. Zero is the lowest and most trusted.
Is a static route always AD 1? Not always. A static route pointing to an outgoing interface has AD 0 by default. Pointing to a next-hop IP gives it 1.
Does AD affect routes inside the same routing protocol? No. AD only compares different sources. Within one protocol, the metric decides.
Why is iBGP administrative distance 200? Because internal BGP assumes your interior gateway protocol already handles trust inside the AS. A high AD keeps iBGP from overriding IGPs by default.
So the next time someone throws that question at you, you'll know it's not a trick. The least default administrative distance goes to the thing the router can literally see plugged in. Everything else is a step down in trust — and once you internalize that order, a lot of weird routing behavior suddenly
starts to make sense.
What to remember most? Because of that, that administrative distance is really just a trust score the router assigns to where a route came from, not how good the path actually is. Practically speaking, a directly connected link wins because the device has physical proof it exists; everything learned from elsewhere carries progressively more doubt. Once you stop treating AD as trivia and start reading it as the router’s built-in skepticism meter, troubleshooting convergence issues and cutover surprises gets a lot easier. Keep the default table in your head, check the codes in your route output, and you’ll never lose a route to a trust mismatch again Worth knowing..
