Administrative Distance
Compare administrative distances across routing protocols to determine the preferred route.
About Administrative Distance
Administrative distance is a per-source trust ranking (0-255, lower is more trusted) that a router uses to choose between multiple routes to the exact same destination prefix learned from different routing sources — it only applies when two routes have identical prefix length; a more specific prefix always wins via longest prefix match regardless of AD. Connected interfaces (AD 0) and static routes (AD 1) are trusted most, since they are directly configured by an administrator, while dynamically learned protocols are ranked by how reliable their information is generally considered, with iBGP (200) and unknown sources (255) trusted least.
Formula
Route source preference
lower administrative distance wins, when prefix lengths are equal
- AD(r)
- Administrative distance of the source that learned route r
Worked example
With the default values below, Administrative Distance returns Preferred (Trusted) Route of OSPF (AD 110) — lower AD wins. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Route Source Aone of Connected (0), Static Route (1), EIGRP Summary Route (5), eBGP (20), EIGRP Internal (90), IGRP (100), OSPF (110), IS-IS (115), RIP (120), EIGRP External (170), iBGP (200), Unknown / Unreachable (255)
- OSPF (110)
- Route Source Bone of Connected (0), Static Route (1), EIGRP Summary Route (5), eBGP (20), EIGRP Internal (90), IGRP (100), OSPF (110), IS-IS (115), RIP (120), EIGRP External (170), iBGP (200), Unknown / Unreachable (255)
- RIP (120)
Results
- Preferred (Trusted) Route
- OSPF (AD 110) — lower AD wins
- Source A Administrative Distance
- 110
- Source B Administrative Distance
- 120
- AD Difference
- 10
Step by step
- 1Values used
- 2Route source preference
- 3Preferred (Trusted) Route= OSPF (AD 110) — lower AD wins
- 4Source A Administrative Distance= 110
- 5Source B Administrative Distance= 120
- 6AD Difference= 10
Assumptions and limits
- The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to whole numbers, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
What are the standard Cisco administrative distance values?
Connected = 0, Static = 1, EIGRP summary route = 5, eBGP = 20, EIGRP internal = 90, IGRP = 100, OSPF = 110, IS-IS = 115, RIP = 120, EIGRP external = 170, iBGP = 200, and an unknown/unreachable source = 255. Lower values are more trusted and preferred when multiple sources offer a route to the identical destination prefix.
Why does eBGP have a much lower AD than iBGP?
Routes learned from an external autonomous system (eBGP, AD 20) are generally treated as more authoritative for reaching that external destination than routes redistributed internally via iBGP (AD 200), which is often carrying information that originated elsewhere in the network and could be less direct or more prone to internal misconfiguration.
Does administrative distance ever get overridden by a metric or prefix length?
Yes, in two ways: administrative distance only decides between routes of the exact same prefix length from different sources — a route with a longer (more specific) prefix always wins regardless of AD. And metric (like OSPF cost or EIGRP composite metric) only matters for choosing between multiple routes within the same protocol/source, not across different sources, where AD applies instead.