RIP (Routing Information Protocol)

1.Core concepts

Algorithm: Uses the Bellman-Ford vector-distance algorithm

Metric: Hop Count. Every router packet passes through counts as 1 hop.

Death Limit The maximum allowed hop count is 15.

Update Timer By default, RIP broadcasts or multicasts its entire routing table to its neighbors every 30 seconds.

2. The differences: RIPv1 vs RIPv2

Feature	RIP version 1 (RIPv1)	RIP version 2 (RIPv2)
Protocol Type	Classful (Does NOT send the subnet mask in routing updates).	Classless (Does send the subnet mask in routing updates).
VLSM / CIDR Support	✗ Not supported. Assumes the default Class A, B, or C mask.	✓ Supported. Allows variable-length subnet masks.
Update Destination	Broadcast (255.255.255.255). Spams every device on the local link.	Multicast (224.0.0.9). Only processed by other RIPv2 routers.
Authentication	✗ Not supported. Clear security risk.	✓ Supported. Supports Plain Text and MD5 authentication.

3. Cisco IOS Configuration

RIPv1

Router(config)# router rip
Router(config-router)# network 192.168.1.0
Router(config-router)# network 10.0.0.0

RIPv2

Router(config)# router rip
Router(config-router)# version 2
Router(config-router)# no auto-summary
Router(config-router)# network 192.168.1.0
Router(config-router)# network 10.0.0.0

Manual summarization

Router(config-router)# interface f1/0
Router(config-if)# ip summary-address rip 10.0.0.0 255.255.0.0

Default route injection

Router(config)# ip route 0.0.0.0 0.0.0.0 203.0.113.2
Router(config)# router rip
Router(config-router)# default-information originate

4. Debugging

Use debug ip rip in privileged EXEC mode to watch RIP updates in real time — routes sent to neighbors, routes received, and metric changes.

Router# debug ip rip
RIP: sending v2 update to 224.0.0.9 via GigabitEthernet0/0 (192.168.1.1)
    192.168.10.0/24 via 0.0.0.0, metric 1, tag 0
RIP: received v2 update from 192.168.1.2 on GigabitEthernet0/0
    10.0.0.0/8 via 0.0.0.0 in 2 hops

What to look for:

• Sending updates — confirms the router is advertising networks on the expected interfaces every 30 seconds.
• Received updates — confirms neighbors are reachable and exchanging routes.
• Metric / hop count — verify the path cost matches the topology (each hop adds 1).

Turn debugging off when finished — debug commands are CPU-intensive and can overwhelm the console in production:

Router# undebug all

Or disable only RIP debugging:

Router# undebug ip rip

Verification without debug — use show ip route rip and show ip protocols for a snapshot of learned routes and RIP timers without live tracing.