RIP Network Statement Not Including All Interfaces
Presenting Symptom
A router running RIP is not advertising routes for some directly connected subnets, causing reachability issues to those networks.
Network Context
The network consists of three routers (R1, R2, R3) in a small branch office, all running RIP version 2. R1 is connected to two subnets: 192.168.1.0/24 and 10.0.0.0/24. The 10.0.0.0/24 subnet is not being advertised to R2 and R3, although it is configured on an interface that is up/up. All routers run IOS 15.x.
Diagnostic Steps
Check RIP routes on a neighbor router
show ip route ripR 192.168.1.0/24 [120/1] via 192.168.2.1, 00:00:15, GigabitEthernet0/0
10.0.0.0/24 is not present in the output.The missing subnet (10.0.0.0/24) is not in the routing table, indicating it is not being advertised by R1.
Examine RIP configuration on R1
show running-config | section router riprouter rip version 2 network 192.168.1.0 network 192.168.2.0
The network statement for 10.0.0.0 is missing. RIP only advertises subnets that match a network statement. The 10.0.0.0/24 subnet is not included.
Verify interface IP addresses on R1
show ip interface briefInterface IP-Address OK? Method Status Protocol GigabitEthernet0/0 192.168.2.1 YES manual up up GigabitEthernet0/1 10.0.0.1 YES manual up up GigabitEthernet0/2 192.168.1.1 YES manual up up
The interface with IP 10.0.0.1 is up/up, confirming the subnet exists and is operational, but not included in RIP.
Check RIP database on R1
show ip rip database192.168.1.0/24 auto-summary 192.168.1.0/24 directly connected, GigabitEthernet0/2 192.168.2.0/24 auto-summary 192.168.2.0/24 directly connected, GigabitEthernet0/0 10.0.0.0/24 is not listed.
The RIP database only contains networks that have a matching network statement. The missing 10.0.0.0/24 confirms it is not being advertised.
Root Cause
The RIP network statement on R1 does not include the 10.0.0.0 subnet. RIP only advertises subnets that fall within the range of a configured network statement. Since 10.0.0.0/24 is not covered by any network statement, it is not advertised to RIP neighbors.
Resolution
Verification
On R2 or R3, run 'show ip route rip' and verify that the 10.0.0.0/24 route appears: R 10.0.0.0/24 [120/1] via 192.168.2.1, 00:00:05, GigabitEthernet0/0 Also on R1, run 'show ip rip database' to confirm the subnet is listed: 10.0.0.0/24 auto-summary 10.0.0.0/24 directly connected, GigabitEthernet0/1
Prevention
1. Always ensure that every directly connected subnet intended for RIP advertisement has a corresponding network statement. 2. Use 'network' commands with the classful network address (e.g., 10.0.0.0) rather than the exact subnet to avoid missing subnets. 3. After configuration, verify RIP advertisements using 'show ip rip database' or 'debug ip rip'.
CCNA Exam Relevance
On the CCNA 200-301 exam, this scenario appears in troubleshooting questions where a router is not advertising a route. The exam tests understanding that RIP network statements are classful and must match the major network of the interface IP. Candidates must know that missing network statements cause routes to be omitted from RIP updates.
Exam Tips
Remember that RIP network statements are classful; 'network 10.0.0.0' includes all subnets of 10.0.0.0/8.
Use 'show ip protocols' to quickly see which networks are being advertised by RIP.
If a route is missing, always check the routing protocol configuration first, not the interface status.
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.
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