Route precedence in Cisco Routers
Only the best route for each learned network/prefix makes it into the routing table. If they don’t have the same prefix
Ex: 192.168.0.0/30 192.168.0.0/28
Although they are overlapping the router adds both routes to the routing table. When a packet arrives, the router looks for the most specific match, the longest prefix.
Criteria for which is the best route to the exact same network/prefix:
Section titled “Criteria for which is the best route to the exact same network/prefix:”1. Administrative Distance (lower value is better)
Section titled “1. Administrative Distance (lower value is better)”Table 1 — Common Administrative Distance (Cisco defaults)
| Source / Protocol | Administrative Distance |
|---|---|
| Connected | 0 |
| Static | 1 |
| eBGP | 20 |
| EIGRP (internal) | 90 |
| IGRP (legacy) | 100 |
| OSPF | 110 |
| IS-IS | 115 |
| RIP | 120 |
| EIGRP (external) | 170 |
| iBGP | 200 |
| Unknown / Not trusted (drop) | 255 |
Lower values are preferred — the route with the lowest administrative distance for the same prefix wins. A value of 255 means the route is considered unreachable and will not be installed in the routing table.
If there is a tie:
2. Metric (lower value is better)
Section titled “2. Metric (lower value is better)”Table 2 — Common Metric Types and How They Work
| Protocol / Source | Metric Type | How it’s calculated / used |
|---|---|---|
| OSPF | Cost | Sum of interface costs (default cost = 10^8 / bandwidth). Lower cost preferred. |
| EIGRP | Composite metric | Uses bandwidth, delay, reliability, load and MTU (by default bandwidth + delay). Lower composite metric preferred. |
| RIP | Hop count | Simple count of hops to destination (max 15 in RIP v2). Lower hop count preferred. |
| BGP | Path attributes | BGP selects best path using a specific attribute order: highest LOCAL_PREF, shortest AS_PATH, lowest origin type, lowest MED (when comparable), eBGP over iBGP, etc. MED is a tie-breaker and is lower-is-better. |
| Static / Connected | Not applicable / 0 | Static and connected routes do not use a routing metric in selection; they are preferred by Administrative Distance. |
Metrics are protocol-specific and are only compared between routes learned via the same protocol (or after protocols are normalized via redistribution). For example, OSPF cost values are only comparable against other OSPF-learned routes; comparing an OSPF cost to an EIGRP composite metric is meaningless — Administrative Distance decides between protocols first.
If there are multiple best routes with the same Administrative Distance and Metric, they will all enter the routing table and the router will perform Equal Cost Load Balancing over them.