The Routing Information Protocol (RIP) is one of the oldest dynamic routing protocols. It is simple to configure and easy to understand, which makes it a classic topic in networking courses. In modern networks, however, OSPF and EIGRP have largely replaced it.
This guide explains how RIP works, its versions, timers and loop-prevention features, a Cisco configuration and when it still makes sense.
How RIP works
RIP is a distance vector protocol. Each router tells its neighbours which networks it can reach and how far away they are. The metric is hop count: the number of routers between the source and the destination.
- The maximum valid hop count is 15.
- A hop count of 16 means “unreachable”.
Because of this limit, RIP only suits small networks. In addition, hop count ignores bandwidth, so RIP may choose a slow two-hop path over a fast three-hop path.
RIP versions
| Feature | RIPv1 | RIPv2 | RIPng |
|---|---|---|---|
| IP version | IPv4 | IPv4 | IPv6 |
| Classful or classless | Classful (no subnet masks) | Classless (VLSM and CIDR) | Classless |
| Updates sent to | Broadcast | Multicast 224.0.0.9 | Multicast FF02::9 |
| Authentication | No | Yes (plain text or MD5) | Relies on IPv6 security features |
| Standard | RFC 1058 | RFC 2453 | RFC 2080 |
For transport, the protocol uses UDP port 520 for IPv4 (RIPng uses UDP 521), and its administrative distance on Cisco devices is 120.
Timers
| Timer | Default | Purpose |
|---|---|---|
| Update | 30 seconds | Sends the full routing table to neighbours |
| Invalid | 180 seconds | Marks a route invalid if no update arrives |
| Hold-down | 180 seconds | Ignores less reliable updates for a recently failed route |
| Flush | 240 seconds | Removes the route from the table |
Because the full table goes out every 30 seconds, RIP converges slowly and wastes bandwidth on large networks.
Preventing routing loops
Distance vector protocols can create loops when a route fails. RIP uses several techniques:
- Split horizon: a router does not advertise a route back out of the interface it learned it from.
- Route poisoning: a failed route is advertised with a metric of 16.
- Poison reverse: a router advertises a poisoned route back to the sender.
- Hold-down timers: stop flapping routes from bouncing back too quickly.
- Triggered updates: changes go out immediately instead of waiting for the next update.
Cisco RIPv2 configuration
router rip
version 2
no auto-summary
network 192.168.10.0
network 10.0.0.0
passive-interface GigabitEthernet0/1The no auto-summary command stops summarisation at classful boundaries, and passive-interface stops updates on user-facing ports.
Verification
show ip protocols
show ip route rip
debug ip ripUse debug only in a lab or carefully in production.
Should you use RIP today?
RIP still appears in small labs, some legacy networks and certain embedded devices. However, for new designs, choose OSPF for multi-vendor networks or EIGRP for Cisco-only networks. Both converge faster, scale better and use more meaningful metrics.
Related guides
Sources
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