RIP Routes Not Propagating Between Routers
Presenting Symptom
RIP routes learned from one router are not being propagated to other routers in the same RIP domain.
Network Context
A small branch office network with three Cisco routers (R1, R2, R3) running RIP version 2. All routers are connected via serial links with IP addresses in the 10.0.0.0/24 range. The network uses Cisco IOS 15.x. The engineer has configured RIP on all routers but notices that routes from R1 are not appearing in the routing table of R3.
Diagnostic Steps
Check RIP routes on the router that should be receiving routes
show ip route ripR 10.1.1.0/24 [120/1] via 10.0.0.2, 00:00:15, Serial0/0/0 R 10.2.2.0/24 [120/2] via 10.0.0.2, 00:00:15, Serial0/0/0
If no RIP routes are shown, the router is not receiving any RIP updates. If some routes are missing, the issue may be specific to certain networks.
Verify RIP configuration on all routers
show running-config | section router riprouter rip version 2 network 10.0.0.0 no auto-summary
Ensure RIP is enabled and the correct networks are advertised. Missing 'network' statements for connected interfaces can prevent route propagation.
Check if passive interfaces are blocking updates
show ip protocols | include PassivePassive Interface(s): GigabitEthernet0/0
If an interface that should be sending RIP updates is listed as passive, it will not send updates. This can cause routes not to propagate.
Check RIP neighbor relationships and update timers
debug ip ripRIP: sending v2 update to 224.0.0.9 via Serial0/0/0 (10.0.0.1) RIP: received v2 update from 10.0.0.2 on Serial0/0/0
If no updates are being sent or received, there may be a connectivity issue or access list blocking RIP traffic (UDP port 520).
Root Cause
The interface connecting R2 to R3 was configured as a passive interface under RIP, preventing R2 from sending RIP updates out that interface. As a result, R3 never learned routes from R1 via R2.
Resolution
Verification
On R3, run 'show ip route rip' and verify that routes from R1 (e.g., 10.1.1.0/24) appear with the correct next-hop (R2's interface IP). Also run 'show ip rip database' to confirm the routes are in the RIP database.
Prevention
1. Avoid using passive-interface on interfaces that need to exchange RIP updates unless specifically required for security. 2. Use 'show ip protocols' to review passive interface configuration after changes. 3. Document all passive interfaces in the network design.
CCNA Exam Relevance
On the CCNA 200-301 exam, this scenario may appear as a troubleshooting question where you must identify why RIP routes are not being exchanged. The exam tests understanding of passive interfaces and their impact on routing protocol updates. A candidate must know that passive interfaces stop sending updates but still receive them.
Exam Tips
Remember that passive-interface stops sending routing updates but still allows receiving updates on that interface.
In RIP, the default version is RIPv1; always check that version 2 is configured if needed.
Use 'show ip protocols' to quickly see passive interfaces and network statements.
Commands Used in This Scenario
debug ip rip
Enables real-time debugging of RIP routing updates to troubleshoot routing issues by displaying sent and received RIP updates.
show ip protocols
Displays the current state of all IP routing protocols running on the router, including timers, filters, and network advertisements.
show ip route
Displays the current IP routing table on a Cisco router, used to verify routes, check next-hop addresses, and troubleshoot connectivity issues.
Test Your CCNA Knowledge
Practice with scenario-based questions to prepare for the CCNA 200-301 exam.
Practice CCNA Questions