RIPCCNA 200-301

RIPv1/v2 Version Mismatch Causing No Updates

Presenting Symptom

Routers configured with RIPv1 and RIPv2 are not exchanging routing updates, resulting in missing routes in the routing table.

Network Context

A small branch office network consists of two Cisco routers (R1 and R2) connected via a serial link. R1 runs RIPv1 and R2 runs RIPv2. Both routers have directly connected networks that should be advertised via RIP. The network uses a classful addressing scheme on R1 and classless on R2.

Diagnostic Steps

Check RIP configuration on both routers

show ip protocols

Routing Protocol is "rip"
  Sending updates every 30 seconds, next due in 16 seconds
  Invalid after 180 seconds, hold down 180, flushed after 240
  Outgoing update filter list for all interfaces is not set
  Incoming update filter list for all interfaces is not set
  Redistributing: rip
  Default version control: send version 1, receive version 1
    Interface             Send  Recv  Key-chain
    Serial0/0/0           1     1
  Routing for Networks:
    192.168.1.0
    10.0.0.0
  Routing Information Sources:
    Gateway         Distance      Last Update
  Distance: (default is 120)

Look at the 'Default version control' line and the per-interface version. If one router shows send/receive version 1 and the other shows version 2, there is a version mismatch.

Check RIP database for received routes

show ip rip database

192.168.1.0/24    auto-summary
192.168.1.0/24    directly connected, Serial0/0/0
10.0.0.0/8    auto-summary
10.0.0.0/8    directly connected, Serial0/0/0

If the database shows only directly connected networks and no routes learned from the neighbor, it indicates that RIP updates are not being received or accepted.

Debug RIP routing updates

debug ip rip

RIP: received v2 update from 192.168.1.2 on Serial0/0/0
     10.0.0.0/8 via 0.0.0.0 in 2 hops
RIP: ignored v2 packet from 192.168.1.2 (illegal version)

If you see 'ignored v2 packet' or 'ignored v1 packet' due to version mismatch, this confirms the root cause. The router is receiving updates but discarding them because the version does not match its configured receive version.

Check interface RIP version configuration

show running-config | section router rip

router rip
 version 1
 network 192.168.1.0
 network 10.0.0.0

If one router has 'version 1' and the other has 'version 2' (or no version command, defaulting to send v1 receive v1/2), the mismatch is confirmed. The router with version 1 will not accept v2 updates.

Root Cause

RIPv1 and RIPv2 are incompatible in their update formats. RIPv1 sends broadcast updates with classful routing, while RIPv2 sends multicast updates with subnet masks. A router configured with RIPv1 will ignore RIPv2 updates and vice versa, unless the receive version is configured to accept both.

Resolution

Configure both routers to use the same RIP version, or configure the interface to send/receive both versions. For example, to use RIPv2 on both: R1(config)# router rip R1(config-router)# version 2 R1(config-router)# exit Alternatively, to allow both versions on an interface: R1(config)# interface serial0/0/0 R1(config-if)# ip rip send version 1 2 R1(config-if)# ip rip receive version 1 2

Verification

R1# show ip route rip 10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks R 10.0.0.0/8 [120/1] via 192.168.1.2, 00:00:12, Serial0/0/0 R1# show ip rip database 10.0.0.0/8 auto-summary 10.0.0.0/8 via 192.168.1.2, Serial0/0/0 R1# debug ip rip RIP: received v2 update from 192.168.1.2 on Serial0/0/0 10.0.0.0/8 via 0.0.0.0 in 1 hops

Prevention

1. Always configure the same RIP version on all routers in the domain. 2. Use RIPv2 for classless routing support and disable auto-summary. 3. If mixing versions is unavoidable, configure interfaces to send/receive both versions.

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 missing. The exam tests understanding of RIP version differences and the ability to interpret debug output. A key fact: RIPv1 sends broadcasts and does not include subnet masks; RIPv2 sends multicasts and includes subnet masks.

Exam Tips

Remember that RIPv1 uses broadcast (255.255.255.255) and RIPv2 uses multicast (224.0.0.9).

If you see 'ignored v1/v2 packet' in debug output, the version mismatch is the likely cause.

The 'show ip protocols' command shows the RIP version configured globally and per interface.

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.

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