RIP Cheat Sheet

MAG212 CYBER · NETWORK ENGINEERING

RIP Ultimate Cheat Sheet

Configuration • Commands • Cisco-style Diagrams • Troubleshooting • Security

Educational technical field guide · Published by MAG212 CYBER · cyber.mag212.com
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01 / RIP in 60 seconds

RIP is a distance-vector interior gateway protocol based on hop count. RIPv2 (RFC 2453) carries subnet masks and uses UDP port 520 with IPv4 multicast 224.0.0.9. RIPng (RFC 2080) supports IPv6 using UDP port 521 and FF02::9. Hop count 15 is the maximum usable metric; 16 means unreachable. Default Cisco administrative distance: 120.

02 / Choosing the version

RIPv1 is classful and obsolete. RIPv2 supports CIDR/VLSM, authentication, and multicast updates. RIPng is the IPv6 variant; it does not simply use RIPv2 IPv4 network statements. These protocols are suitable primarily for labs, interoperability, or constrained legacy environments—not modern large enterprise routing.

03 / Packet exchange and convergence

A router periodically advertises its known destinations. Receiving routers increment the hop-count metric, compare candidates, and update their routing table. Split horizon, route poisoning (metric 16), triggered updates, and hold-down behavior help limit looping or stale routes, but convergence can still be slower than OSPF or EIGRP.

04 / Timer quick reference

Typical Cisco defaults: Update 30 seconds, Invalid 180 seconds, Hold-down 180 seconds, Flush 240 seconds. Verify platform behavior before changing timers. Inconsistent timers and filtering can create oscillation or route loss.

05 / Original Cisco-style three-router lab

Diagram uses two /30 point-to-point IPv4 links and three documentation-only IPv4 LAN prefixes. RIPv2 is enabled on connected networks; LAN-facing interfaces are passive so their networks are advertised but user segments do not receive RIP updates.

RIPv2 three-router lab topologyR1, R2 and R3 in a line joined by two point-to-point /30 links. Each router has a passive user LAN. R1 learns the R2 LAN at 1 hop and the R3 LAN at 2 hops.MAG212 CYBER· RIPv2 ROUTING LABThree routers · point-to-point /30 transit links · passive user LANs · documentation addressing10.212.12.0/30R1 Gi0/0/0 .1 ↔ R2 Gi0/0/0 .2RIPv2 updates · UDP 520 → 224.0.0.910.212.23.0/30R2 Gi0/0/1 .1 ↔ R3 Gi0/0/0 .2RIPv2 updates · UDP 520 → 224.0.0.9R1 · EDGE192.0.2.0/24Gi0/0/1 · 192.0.2.1passive · advertised, no updates sentR2 · CORE198.51.100.0/24Gi0/0/2 · 198.51.100.1passive · advertised, no updates sentR3 · BRANCH203.0.113.0/24Gi0/0/1 · 203.0.113.1passive · advertised, no updates sentR1 routing table after convergence: R 198.51.100.0/24 [120/1] via 10.212.12.2 · R 203.0.113.0/24 [120/2] via 10.212.12.2Metric = hop count · connected = 0 · each router adds 1 · 15 is the maximum · 16 = unreachable

Diagram: two point-to-point /30 transit links and three passive user LANs. Interface names and addresses match the configurations in section 06. RIP has no router ID; routers are identified only by their interface addresses.

06 / RIPv2 configurations

Apply the configuration for each router below. Interface names assume a lab platform with GigabitEthernet0/0/x; adapt names to your device. Network statements in Cisco RIPv2 use classful major network values, while no auto-summary ensures classless prefixes are advertised.

R1 — EDGE

hostname R1
interface GigabitEthernet0/0/0
 description TO-R2
 ip address 10.212.12.1 255.255.255.252
 no shutdown
interface GigabitEthernet0/0/1
 description LAN-192.0.2.0
 ip address 192.0.2.1 255.255.255.0
 no shutdown
router rip
 version 2
 no auto-summary
 network 10.0.0.0
 network 192.0.2.0
 passive-interface default
 no passive-interface GigabitEthernet0/0/0

R2 — CORE

hostname R2
interface GigabitEthernet0/0/0
 description TO-R1
 ip address 10.212.12.2 255.255.255.252
 no shutdown
interface GigabitEthernet0/0/1
 description TO-R3
 ip address 10.212.23.1 255.255.255.252
 no shutdown
interface GigabitEthernet0/0/2
 description LAN-198.51.100.0
 ip address 198.51.100.1 255.255.255.0
 no shutdown
router rip
 version 2
 no auto-summary
 network 10.0.0.0
 network 198.51.100.0
 passive-interface default
 no passive-interface GigabitEthernet0/0/0
 no passive-interface GigabitEthernet0/0/1

R3 — BRANCH

hostname R3
interface GigabitEthernet0/0/0
 description TO-R2
 ip address 10.212.23.2 255.255.255.252
 no shutdown
interface GigabitEthernet0/0/1
 description LAN-203.0.113.0
 ip address 203.0.113.1 255.255.255.0
 no shutdown
router rip
 version 2
 no auto-summary
 network 10.0.0.0
 network 203.0.113.0
 passive-interface default
 no passive-interface GigabitEthernet0/0/0

07 / Expected routing outcomes

After convergence, R1 should learn 198.51.100.0/24 via 10.212.12.2 with metric 1, and 203.0.113.0/24 via the same next hop with metric 2. R3 should learn 192.0.2.0/24 with metric 2. The routing table generally displays an R and administrative distance/metric pair, e.g., [120/2].

08 / RIPng configuration

Enable IPv6 forwarding globally, assign documentation-prefix IPv6 addresses to interfaces, then enable named RIPng per participating interface. IOS XE RIPng uses ipv6 rip NAME enable; exact support depends on image and platform. Do not reuse IPv4 route filters for IPv6 without checking their syntax.

Note: as written, RIPng also sends updates on the LAN interfaces (Gi0/0/1, and Gi0/0/2 on R2). In production, keep routing updates off user segments, for example with an IPv6 ACL that drops UDP 521 from untrusted hosts, and check whether your release offers a passive option for RIPng.

R1 (IPv6)

ipv6 unicast-routing
interface GigabitEthernet0/0/0
 ipv6 address 2001:db8:12::1/64
 ipv6 rip M212 enable
interface GigabitEthernet0/0/1
 ipv6 address 2001:db8:101::1/64
 ipv6 rip M212 enable
ipv6 router rip M212

R2 (IPv6)

ipv6 unicast-routing
interface GigabitEthernet0/0/0
 ipv6 address 2001:db8:12::2/64
 ipv6 rip M212 enable
interface GigabitEthernet0/0/1
 ipv6 address 2001:db8:23::1/64
 ipv6 rip M212 enable
interface GigabitEthernet0/0/2
 ipv6 address 2001:db8:102::1/64
 ipv6 rip M212 enable
ipv6 router rip M212

R3 (IPv6)

ipv6 unicast-routing
interface GigabitEthernet0/0/0
 ipv6 address 2001:db8:23::2/64
 ipv6 rip M212 enable
interface GigabitEthernet0/0/1
 ipv6 address 2001:db8:103::1/64
 ipv6 rip M212 enable
ipv6 router rip M212

09 / Verification command reference

CommandWhat it shows
show ip protocolsprotocol state, networks and timers
show ip route riproutes installed from RIP
show ip rip databaseRIP database including learned routes
show running-config | section router ripRIP process configuration
show ipv6 rip M212 databaseIPv6 RIP learned information
show ipv6 route ripIPv6 routes installed from RIP
debug ip rippacket debugging; use cautiously in a lab
undebug allimmediately disable debugging

10 / Troubleshooting playbook

No routes? Check interfaces and IP masks; ping the directly connected next hop; ensure router rip, version 2, correct network statements, and no auto-summary. Look for passive-interface blocking a transit connection, ACLs blocking UDP 520, authentication mismatches, route filtering, competing routes with lower administrative distance, and hop count 16. For RIPng inspect link-local reachability, IPv6 forwarding, and per-interface activation.

11 / Secure deployment checklist

Avoid RIP on untrusted interfaces. Passive LAN edges; authenticate RIPv2 peers with a supported key chain and MD5 when RIP must be used (MD5 is legacy and not encryption); filter advertised and accepted prefixes; restrict management access; log unexpected route changes; avoid indiscriminate redistribution; prefer an authenticated modern IGP where possible.

! RIPv2 MD5 authentication — same key number and key-string on both ends of the link
key chain RIP-KEYS
 key 1
  key-string REPLACE-WITH-STRONG-SECRET
!
interface GigabitEthernet0/0/0
 ip rip authentication mode md5
 ip rip authentication key-chain RIP-KEYS

RIPng has no native RIP-specific authentication—use network-layer controls such as IPsec where supported or isolate the routing segment.

12 / Common interview questions

Why is a route with 16 hops discarded?

RIP defines 16 as infinity, making it unusable.

Why no auto-summary?

To preserve subnets over classful network boundaries.

What does passive-interface do?

Suppresses RIP announcements on that interface while its matching connected network can still be advertised elsewhere.

Why might a valid RIP route not appear in show ip route?

Another route may win on administrative distance.

Which UDP ports?

520 for RIPv1/v2; 521 for RIPng.

Is RIPv2 authentication encrypted?

No; MD5 authenticates the update but does not encrypt route information.

13 / Operational cautions

Validate every configuration in a lab before production. Router images differ and some legacy syntax is absent from newer platforms.

14 / Sources & verification

This is an original MAG212 CYBER guide. The lab, diagram and explanations were written independently and checked against the standards and Cisco documentation below.

RFC 2453 — RIP Version 2
RFC 2080 — RIPng for IPv6
Cisco — IPv6 Routing: RIP for IPv6 (IOS XE)
Cisco — Sample Configuration for Authentication in RIPv2

MAG212 CYBER · NETWORK ENGINEERING · RIP ULTIMATE CHEAT SHEET
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