CCNA online course

RIP Configuration on Cisco Routers

Learn how to configure, verify, and troubleshoot RIPv2 on Cisco IOS routers, including network statements, auto-summary, passive interfaces, default routes, timers, and common failures.

Routing Information Protocol (RIP) is an interior gateway protocol (IGP) that exchanges IPv4 route information between routers inside one organization or routing domain. This lesson covers Cisco IOS configuration, RIPv1 and RIPv2 behavior, verification, default-route advertisement, loop avoidance, and troubleshooting.

You should understand IPv4 addressing, subnet masks, VLSM, Cisco IOS command modes, interface status, connected routes, static routes, and routing-table interpretation before starting.

Purpose of RIP

RIP is a distance-vector routing protocol. A distance-vector protocol learns reachability from neighboring routers. Each advertisement includes a destination and a distance to that destination.

RIP measures distance with hop count. A hop is one router crossed on the way to a destination. RIP does not select a path based on bandwidth, delay, or link reliability.

  • RIP is simple to configure and useful for small, uncomplicated IPv4 networks and learning labs.
  • RIP sends periodic routing updates, so changes may take longer to propagate than with more modern protocols.
  • RIP is generally unsuitable for large or complex enterprise networks because of its hop-count limit and slower convergence.

RIP Route Selection and Limitations

Hop count and administrative distance

RIP chooses the route with the lowest hop-count metric. A directly connected destination learned through RIP has a metric of one from a neighboring router; each additional router increases the metric by one.

  • 15 hops: the greatest usable RIP distance.
  • 16 hops: unreachable, also called an infinite metric.
  • Administrative distance: Cisco IOS normally assigns RIP routes an administrative distance of 120. When several routing sources know the same destination, IOS generally prefers the source with the lower administrative distance before comparing that protocol's metric.

If multiple RIP routes to the same destination have equal metrics, Cisco IOS can install multiple equal-cost paths and load-balance traffic across them, subject to platform and routing-table limits.

Updates and convergence

RIP periodically sends its routing information to neighbors. Periodic updates allow routers to refresh routes, but they also mean that a failure is not necessarily known immediately. Invalid, hold-down, and flush timers determine how long route information is retained during failures and instability.

RIPv1 Compared with RIPv2

RIPv1 is classful: its updates do not include subnet mask information. RIPv2 is classless: its updates include the prefix length, allowing routers to distinguish different subnet sizes.

  • VLSM means Variable Length Subnet Masking, where different prefix lengths are used in one address plan.
  • CIDR means Classless Inter-Domain Routing, which uses prefix-based addressing and aggregation rather than fixed address classes.
  • RIPv1 sends updates by IPv4 broadcast.
  • RIPv2 normally sends updates to multicast address 224.0.0.9.
  • RIPv2 supports authentication at a conceptual level, allowing routers to validate routing updates.

RIPv2 is normally preferred for modern IPv4 labs because it supports VLSM and CIDR and carries the mask with each route. Version compatibility should still be checked on every router and transit interface.

Feature comparison

  • RIPv1: classful, no mask in updates, broadcast updates, unsuitable for many VLSM designs.
  • RIPv2: classless, prefix length in updates, multicast updates to 224.0.0.9, supports VLSM, CIDR, and authentication.
  • Operational impact: use RIPv2 when subnet masks must be preserved or when the topology contains discontiguous networks.

Three-Router RIPv2 Lab

Use a line topology with one LAN behind each router:

  • R1 LAN: 192.168.10.0/24
  • R1–R2 transit link: 10.0.12.0/30
  • R2 LAN: 192.168.20.0/24
  • R2–R3 transit link: 10.0.23.0/30
  • R3 LAN: 192.168.30.0/24

Each router advertises its directly connected LAN and transit networks. Replace the example network addresses with the addresses used in your lab.

R1 configuration

enable
configure terminal
router rip
 version 2
 no auto-summary
 network 192.168.10.0
 network 10.0.0.0
end
copy running-config startup-config

R2 configuration

enable
configure terminal
router rip
 version 2
 no auto-summary
 network 192.168.20.0
 network 10.0.0.0
end
copy running-config startup-config

R3 configuration

enable
configure terminal
router rip
 version 2
 no auto-summary
 network 192.168.30.0
 network 10.0.0.0
end
copy running-config startup-config

The IOS network statement does not specify a remote destination. It matches local interfaces whose addresses belong to the specified network. Matching interfaces participate in RIP, and their connected prefixes can be advertised to neighbors.

On some IOS versions, a classful network statement such as network 10.0.0.0 activates RIP on matching interfaces within that major network. Always confirm the result with show ip protocols and the routing table.

Classful and Classless Behavior

Automatic summarization

Auto-summary summarizes routes at classful network boundaries. For example, subnets of a major network may be advertised as the larger classful network when crossing that boundary.

This can create incorrect or ambiguous routing in a discontiguous design. Imagine two separated groups using subnets from 172.16.0.0/16, with another address range between them. A classful summary of 172.16.0.0/16 may cause a router to choose a path that does not lead to the intended subnet. VLSM networks can also lose the specific masks required for correct forwarding.

For RIPv2 designs that require classless advertisement, disable summarization:

configure terminal
router rip
 version 2
 no auto-summary
end

Verify the result by checking whether the routing table contains the expected prefixes, such as 172.16.10.0/24, rather than only a broad classful summary.

Controlling RIP Participation

Passive interfaces

A passive interface does not send RIP updates through that interface, but the connected network can still be advertised through other RIP-enabled interfaces. This is appropriate for a user-facing LAN where no router neighbor exists.

configure terminal
router rip
 passive-interface GigabitEthernet0/0
end

Keep a router-to-router interface non-passive so neighboring routers can exchange updates. Making the transit interface passive can stop route learning even though the interface is physically operational.

Passive by default

In a larger configuration, make every interface passive first, then enable updates only on known router links:

configure terminal
router rip
 passive-interface default
 no passive-interface GigabitEthernet0/1
end

To remove RIP participation from an interface, remove the matching passive or non-passive policy as appropriate and remove the relevant network statement when the local network should no longer be advertised. Confirm the resulting process configuration afterward.

Default Route Advertisement

A default route is used when no more-specific route matches a destination. An edge router can install a static default route toward an upstream gateway and then originate that route into RIP.

configure terminal
ip route 0.0.0.0 0.0.0.0 203.0.113.1
router rip
 version 2
 default-information originate
end

The edge router should have a valid default route in its routing table before originating it. On an internal router, inspect the routing table for a RIP-learned default route and a gateway of last resort. If the edge router loses its usable default, verify whether the platform withdraws the originated route according to its current IOS behavior and configuration.

RIP Timers and Loop Avoidance

  • Periodic update timer: controls regular routing advertisements.
  • Invalid timer: determines when a route that has not been refreshed is considered invalid.
  • Hold-down timer: causes unstable route information to be treated cautiously for a period, reducing the chance of accepting misleading updates.
  • Flush timer: determines when an invalid route is removed from the routing table and database.

Timer values and behavior can vary by IOS release and should be confirmed with the device documentation and show ip protocols. Frequent updates and timer expiration affect convergence speed.

Split horizon prevents a router from advertising a route back through the interface on which it learned that route. This reduces simple distance-vector loops.

Route poisoning advertises a failed route with metric 16, marking it unreachable. Poison reverse advertises that unreachable metric back toward the router from which the route was learned. These mechanisms, together with hold-down behavior and split horizon, reduce but do not eliminate distance-vector looping and convergence problems.

Verification and Monitoring

Verify basic interface operation before diagnosing RIP. A routing protocol cannot exchange useful updates over an interface that is administratively down, physically down, incorrectly addressed, or connected to the wrong subnet.

show ip interface brief
show running-config | section router rip
show ip protocols
show ip route
show ip route rip
show ip rip database
ping <destination-ip>
traceroute <destination-ip>
  • show ip interface brief confirms interface addresses and operational status.
  • show running-config | section router rip displays the RIP process, version, network statements, passive interfaces, and default-route configuration.
  • show ip protocols summarizes the active RIP version, networks being advertised, passive interfaces, timers, and auto-summary state.
  • show ip route rip limits the routing-table view to RIP-learned routes.
  • show ip rip database displays RIP's learned route information and metrics.
  • ping tests reachability. traceroute or an IOS traceroute-style command identifies the forwarding path and where it stops.

Reading a RIP route

A routing-table entry such as R 192.168.30.0/24 [120/2] via 10.0.23.2, ... can be interpreted as follows:

  • R: the route was learned by RIP.
  • /24: the installed prefix length.
  • 120: the administrative distance for RIP.
  • 2: the RIP hop-count metric.
  • via 10.0.23.2: the next-hop router.
  • The remaining information identifies the outgoing interface and route age, depending on IOS output.

Use controlled debugging only when show commands do not identify the fault:

debug ip rip
undebug all

Common RIP Failures

  • No remote route: check missing network statements, incorrect interface masks, shutdown interfaces, and the neighbor's RIP configuration. Inspect show ip protocols, show ip route, and show ip rip database.
  • Different RIP versions: compare version settings. Configure compatible RIPv2 operation where classless updates are required.
  • Unexpected classful mask: check for RIPv1 or enabled auto-summary. Use RIPv2 and no auto-summary for VLSM or discontiguous networks.
  • Passive transit link: remove passive status from the router-facing interface. A passive LAN can still advertise its connected prefix, but a passive transit link cannot exchange updates.
  • Incorrect or overlapping networks: compare interface addresses and masks with the addressing plan. Correct overlaps and ambiguous prefixes before changing RIP settings.
  • Layer-1 or Layer-2 failure: verify cabling, interface state, VLAN or encapsulation settings where relevant, and matching IP subnet membership.
  • More than 15 hops: inspect the metric and trace the path. Redesign the topology or migrate to a more scalable protocol.
  • No gateway of last resort: verify that the edge router has a usable default route, that default-information originate is configured, and that RIP updates reach internal routers.

Classifying the fault

  1. Route advertisement: does the local router include the connected network and is the correct interface participating?
  2. Route reception: does the neighbor send updates and does the local RIP database contain the route?
  3. Route selection: did IOS reject the route because of administrative distance, a better route source, an incorrect mask, or an unreachable metric?
  4. Packet forwarding: does the routing table contain a usable next hop, and do interface, ARP, switching, and return-path checks succeed?

Removing RIP and Migration Awareness

Remove an individual network statement when that connected network should no longer participate:

configure terminal
router rip
 no network 192.168.10.0
end

To disable the entire RIP process, first review the impact on routes that depend on it, then remove the process:

configure terminal
no router rip
end
copy running-config startup-config

RIP can be replaced by more scalable protocols such as OSPF or EIGRP as a network grows. See the OSPF configuration lesson for a common alternative and the OSPF route summarization lesson for larger addressing designs.

Exam-Ready Summary

  • RIP is an IPv4 distance-vector IGP that uses hop count.
  • 15 is the maximum reachable metric; 16 means unreachable.
  • Cisco IOS uses administrative distance 120 for RIP by default.
  • RIPv1 is classful and broadcasts updates without subnet masks.
  • RIPv2 is classless, supports VLSM and CIDR, and uses multicast 224.0.0.9.
  • router rip enters RIP configuration mode; network activates RIP on matching local interfaces.
  • Use no auto-summary for classless designs that need specific prefix lengths.
  • Use passive interfaces on end-user LANs, not on router-to-router links that must exchange updates.
  • Originate a default route only when the edge router has a valid default route.
  • Use show ip protocols, show ip route rip, and show ip rip database to verify operation.