CCNA 200-301 v1.1 reference — IP Connectivity
Route selection and forwarding
How a router installs routes (administrative distance, metric) versus how it forwards packets (longest-prefix match, then next hop).
Objective 3.2v1.1 exam target
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The three rules in order
- Forwarding decision (packet in hand): longest-prefix match wins — always, regardless of route source.
- Installation decision (two sources offer the SAME prefix): lowest administrative distance wins the RIB.
- Within one protocol (same prefix, same protocol): lowest metric wins.
Which rule applies when
| Situation | Decided by |
|---|---|
| /24 via OSPF vs /16 via static — packet to a host in the /24 | Longest prefix → the /24 wins |
| 10.0.0.0/24 learned via OSPF and via static | AD → static (1) beats OSPF (110) |
| 10.0.0.0/24 learned twice inside OSPF | Metric → lower cost path wins |
| Only a default route exists | Longest prefix → 0.0.0.0/0 matches |
| Two static routes for the same prefix, different next hops | Same AD → both install; ECMP load-balances |
Predict the forwarding path
- Table
- S 10.0.0.0/8 [1/0], O 10.1.0.0/16 [110/20], C 10.1.5.0/24 (Gi0/1)
- Packet
- to 10.1.5.9
- Candidates: /8 (S), /16 (O), /24 (C) — all match 10.1.5.9.
- Longest prefix wins → /24 connected route forwards directly out Gi0/1.
- The static and OSPF routes never see this packet despite their sources.
AD never entered the picture — the connected /24 is simply the most specific match.
Verifying the decision
show ip route <address>shows the actual match the router will use — the single best debug.- If the match is a more-specific route than you expected, the table is working correctly — your expectation wasn't.
show ip ospf rib/ protocol-specific views show the losing candidates that never installed.
Related resources
Sources
- Cisco CCNA 200-301 v1.1 Exam Topics (official PDF) — reviewed 2026-11-02
Targets CCNA 200-301 v1.1 objectives. Supplemental blocks are labeled beyond exam scope.