The Routing Information Protocol is the oldest routing protocol you will still meet, and the clearest introduction to distance-vector routing: each router knows only what its neighbours tell it — a list of destinations, each with a distance (metric) and a direction (next hop). No router holds a map of the topology; routing is literally routing by rumour.
RIPv2 (RFC 2453) fixed the fatal flaws of RIPv1. It carries the subnet mask in every route entry, making it classless and VLSM-capable; it sends updates to multicast 224.0.0.9 instead of broadcast; and it supports authentication. The metric stayed the same: hop count, with 16 defined as infinity — any destination 16 hops away is unreachable.
The update cycle and the four timers
- Update (30 s) — the full routing table is advertised out every RIP interface, every 30 seconds, jittered slightly to stop update synchronisation.
- Invalid (180 s) — a route not refreshed for 180 seconds is marked invalid (metric 16) but kept in the table while the router advertises its death.
- Holddown (180 s) — after a route goes invalid, better news about it is ignored for the holddown period, damping flapping routes at the cost of slower recovery.
- Flush (240 s) — 60 seconds after going invalid, the route is deleted entirely.
Add these up and RIP's worst-case convergence is measured in minutes — its defining weakness.
Configuration
RIPv2 configuration on Cisco IOS is four lines plus discipline. The network statement is classful — network 10.0.0.0 enables RIP on every interface with an address in 10.0.0.0/8 — so passive-interface control matters. Always disable auto-summary: without it RIPv2 still summarises at classful boundaries and breaks discontiguous subnets, silently.
R1(config)# router ripR1(config-router)# version 2R1(config-router)# no auto-summaryR1(config-router)# network 10.0.0.0R1(config-router)# network 192.168.12.0R1(config-router)# passive-interface gi0/1
Verification
Three commands tell you everything: show ip protocols (timers, networks, neighbours, version), show ip route rip (learned routes — flagged R with administrative distance 120), and debug ip rip when you need to watch updates in real time on a lab router.
R1# show ip route ripR 172.16.2.0/24 [120/2] via 10.1.12.2, 00:00:14, GigabitEthernet0/0R 172.16.3.0/24 [120/1] via 10.1.12.2, 00:00:14, GigabitEthernet0/0
Read the bracket as [administrative distance / metric]: 120 is RIP's trust level relative to other protocols, and the metric is plain hop count. The timestamp shows seconds since the last update — on a healthy RIP network it never exceeds 30. RIPv2 survives today mostly in small or legacy environments and in labs, but the concepts it teaches — periodic advertisement, metric infinity, holddown — are the vocabulary the next chapter uses to explain why it had to be replaced.