Administrative Distance¶

A router-local preference assigned to a route source so the routing information base can choose among candidate routes to the same prefix learned by otherwise incomparable mechanisms.

Version: v4 · 2026-09-19 · History
Domain-specific #: 1244
Domain group: Applied Sciences & Engineering
Origin domain: Computer Science & Software Engineering
Subdomains: Computer Networking, Route Selection and Routing Information Bases → Computer Science & Software Engineering
Aliases: Route preference, Route-source preference, Administrative route distance

Core Idea¶

Administrative distance is a router-local preference attached to the source of a route. It lets a routing information base choose among candidate routes to the same destination prefix when those routes were learned through mechanisms whose native metrics are not directly comparable—for example, a static route, OSPF, RIP, or BGP.

The recurring operation is:

same-prefix candidate routes + source-specific local preference + lower-is-better comparison + platform tie rules → active route or route set in the local routing table.

Cisco calls the value administrative distance; Junos documentation commonly calls it route preference and explicitly identifies that as administrative distance. The number is not a measured geographic distance, hop count, latency, or universal probability of truth.

How would you explain it like I'm…

The Router's Trust List

A router is a box that sends internet messages the right way. Sometimes several helpers tell it different ways to the same place, and each helper measures in its own way. So the router keeps its own trust list of helpers, and a smaller number means "trust this helper first." That number is called administrative distance.

Route Source Ranking

Routers learn directions to places on the internet from different sources, like a route a person typed in by hand or routing programs with names like OSPF and RIP. Each source judges routes with its own kind of score, so the scores can't be compared, like comparing miles with minutes. Administrative distance is a ranking the router gives to each source, and lower wins. When two sources offer a route to the same place, the router uses the one from the better-ranked source. Despite the name, it isn't a real distance; it's the router's own preference.

Router-Local Route-Source Preference

Administrative distance is a number a router attaches to each source of routing information, like a manually set static route or a routing protocol such as OSPF, RIP or BGP. When two sources offer routes to the exact same destination, the router can't just compare their metrics, because an OSPF cost and a RIP hop count mean different things. Instead it compares administrative distances, and the lower value usually wins and goes into the routing table. It is not a measure of distance, hops, speed or how likely a route is correct; it's a local policy ranking. It only matters on that router: it isn't sent to other routers, and changing it doesn't change the protocols' own metrics. Cisco calls it administrative distance, and Junos calls it route preference.

Administrative distance is a router-local preference value attached to the source of a route, used when a routing information base (RIB) must choose among candidate routes to the same destination prefix learned from different mechanisms. The problem it solves is metric incommensurability: an OSPF cost, a RIP hop count, an EIGRP composite metric and the BGP decision process are not in a common unit. Each source first computes candidates under its own rules; the RIB then compares administrative distances, lower normally preferred, with platform-specific tie rules, to decide which source's route becomes active. Cisco uses the term administrative distance, while Junos documentation calls it route preference and identifies the two. It is a policy rank defined by implementation and configuration, not a physical distance, latency, hop count or probability of correctness. It has only local significance: it is not advertised as an end-to-end attribute, and changing it reorders sources on that router alone without altering any protocol's carried metric.

Scope of Application¶

Administrative distance applies to IP routing implementations that maintain multiple candidate sources for a routing table. It appears in enterprise routing, service-provider routers, virtual routing and forwarding instances, network migrations, route redistribution, static/dynamic coexistence, and controlled failover designs.

The abstraction includes default source preferences, protocol-wide overrides, and finer-grained source or prefix adjustments where the platform supports them. It includes the use of a high-distance static route as a standby for a dynamically learned route. It also includes operational inspection of RIB entries that display both source distance and protocol metric.

Clarity¶

Use this diagnostic sequence:

Confirm that the candidates are for the same routing table and destination prefix.
Identify how each route was learned and whether each source has already run its own best-path logic.
Read the effective local administrative distance or route preference after all policy overrides.
Prefer the lower value under the platform's documented comparison order.
If values tie, follow the platform's explicit tie or multipath rules rather than inventing a universal rule.

Manages Complexity¶

A router running several routing protocols receives claims produced by different algorithms and measurement units. Administrative distance reduces this heterogeneous arbitration problem to a small local ordering over sources. The router need not translate OSPF cost into RIP hops or BGP attributes into EIGRP composite metric.

Abstract Reasoning¶

Administrative distance licenses ordinal predictions. If two valid same-prefix candidates reach a RIB from different sources and all earlier eligibility checks pass, lowering one candidate's effective distance below the other normally makes it the preferred source. Raising a static route's distance above a dynamic source can make the static route float; withdrawal of the preferred route then triggers reevaluation and possible standby installation.

Knowledge Transfer¶

Within networking, the abstraction transfers across vendors as a role pattern: source label, local ordinal preference, same-prefix arbitration, active installation, and reevaluation. Literal commands and numbers must be remapped to the target operating system.

The portable skeleton is Prioritization: competing claims receive an ordering that determines which proceeds under a constraint. Selection describes the resulting survivor set. Fallback Path explains one engineered use when a secondary route is intentionally given a worse preference. These primes do not carry routing-specific separation among protocol metrics, RIB source arbitration, and forwarding lookup.

Relationships to Other Abstractions¶

Current abstraction Administrative Distance Domain-specific

Parents (1) — outgoing typed relations

Administrative Distance is a kind of Prioritization Prime

The broader abstraction is Prioritization.

Hierarchy paths (3) — routes to 3 parentless roots

Administrative Distance → is a kind of Prioritization → is a kind of Optimization

Show alternative paths (2)

Neighborhood in Abstraction Space¶

Administrative Distance sits in a sparse region of the domain-specific corpus (90^th percentile for distinctiveness): few abstractions share its structure, so a faithful description tends to retrieve it precisely.

Family — Unclustered & Miscellaneous (2769 abstractions)

Nearest neighbors

Computed from structural-signature embeddings · 2026-10-25