RIPv2 (Routing Information Protocol version 2) is a distance-vector routing protocol that, while old, remains a CCNA 200-301 exam topic (Objective 3.3) because it teaches fundamental routing concepts like hop count, split horizon, and route poisoning. Understanding RIPv2 gives you a clear, simple foundation before moving to more complex protocols like OSPF and EIGRP. In the real world, RIPv2 is rarely used in modern networks, but it appears in legacy environments and as a learning tool for routing principles.
Jump to a section
Imagine a small town where each person (router) needs to know how to deliver mail to every other house (network). There is no central map—each person only knows their immediate neighbors. Every 30 seconds, the town crier (RIP update) walks through the streets and shouts a list of all houses they know how to reach, along with how many steps (hops) away each house is. When you hear the crier, you write down that information, adding one step for yourself (since you are one hop further). If you already know a shorter path, you ignore the longer one. If you stop hearing from a neighbor for 180 seconds (six missed cries), you assume that neighbor has moved away and mark all routes through them as invalid (16 hops = infinity). To prevent loops, the town has a rule: never shout back a route to the person who told you about it (split horizon). If a road is blocked, the crier announces that route with 16 hops (poison reverse) to ensure everyone removes it. This simple, periodic shouting method works for small towns but becomes chaotic in large cities—just like RIPv2 works in small networks but struggles with scalability.
What is RIPv2 and Why Does It Exist?
RIPv2 is a distance-vector routing protocol defined in RFC 2453. It is an enhancement of RIPv1, adding support for classless routing (VLSM and CIDR) by including subnet mask information in updates. RIPv2 uses UDP port 520 and sends updates to multicast address 224.0.0.9 (instead of broadcast in v1). It is still a distance-vector protocol, meaning each router knows only the distance (metric) and direction (next-hop) to each destination, not the full topology.
How RIPv2 Works Step by Step
1. Initialization: When a router boots up and RIPv2 is enabled on an interface, it sends a request message out that interface to ask neighbors for their routing tables. 2. Response/Update: Neighbors respond with their entire routing table (or a triggered update if changes occur). The router receives these updates and processes each route. 3. Route Selection: For each destination network, the router compares the received metric (hop count) plus 1 to its existing metric. If the new metric is smaller, it updates the route; if equal, it may load-balance (up to 4 equal-cost paths by default); if larger, it ignores it (unless it is from the same next-hop, in which case it updates even if metric is larger—this handles route changes). 4. Timers: - Update Timer: 30 seconds. Periodic full routing table updates are sent. - Invalid Timer: 180 seconds (6 missed updates). If no update received for a route, the route is marked as invalid (metric set to 16). - Holddown Timer: 180 seconds. After a route is marked invalid, the router waits before accepting new info about that route to prevent flapping. - Flush Timer: 240 seconds. After the invalid timer expires, the router waits another 60 seconds before removing the route entirely. 5. Loop Prevention: - Split Horizon: Never advertise a route back out the interface from which it was learned. - Route Poisoning: When a route fails, the router advertises it with metric 16 (infinity). - Holddown: While a route is in holddown, the router ignores new updates for that route (unless from the same neighbor that originally advertised it).
RIPv2 Packet Format
RIPv2 uses the same basic packet structure as RIPv1 but adds fields. Each RIP entry (route) is 20 bytes:
Address Family Identifier (AFI): 2 bytes (2 for IP)
Route Tag: 2 bytes (for routing policy, e.g., redistributed routes)
IP Address: 4 bytes
Subnet Mask: 4 bytes (this is the key addition in v2)
Next Hop: 4 bytes (can specify a different next-hop than the source)
Metric: 4 bytes (hop count, 1-15 valid, 16 = infinity)
IOS CLI Configuration and Verification
To configure RIPv2 on a Cisco router:
Router(config)# router rip
Router(config-router)# version 2
Router(config-router)# network 10.0.0.0
Router(config-router)# network 192.168.1.0
Router(config-router)# no auto-summaryversion 2 enables RIPv2 (default is v1 if not specified).
network commands enable RIP on interfaces belonging to those classful networks. RIP will advertise the subnets directly connected.
no auto-summary disables automatic summarization at classful boundaries (RIPv2 supports VLSM, so auto-summary should be off for proper subnet advertisement).
Verification commands:
Router# show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override
Gateway of last resort is not set
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
R 10.1.1.0/24 [120/2] via 192.168.1.2, 00:00:12, GigabitEthernet0/0
C 10.1.2.0/24 is directly connected, GigabitEthernet0/1
192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.1.0/24 is directly connected, GigabitEthernet0/0
L 192.168.1.1/32 is directly connected, GigabitEthernet0/0Router# show ip protocols
*** IP Routing is NSF aware ***
Routing Protocol is "rip"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Sending updates every 30 seconds, next due in 16 seconds
Invalid after 180 seconds, hold down 180, flushed after 240
Redistributing: rip
Default version control: send version 2, receive version 2
Interface Send Recv Triggered RIP Key-chain
GigabitEthernet0/0 2 2
GigabitEthernet0/1 2 2
Automatic network summarization is not in effect
Maximum path: 4
Routing for Networks:
10.0.0.0
192.168.1.0
Routing Information Sources:
Gateway Distance Last Update
192.168.1.2 120 00:00:16
Distance: (default is 120)Router# show ip rip database
10.0.0.0/8 auto-summary
10.1.1.0/24
[2] via 192.168.1.2, 00:00:03, GigabitEthernet0/0
10.1.2.0/24 directly connected, GigabitEthernet0/1
192.168.1.0/24 auto-summary
192.168.1.0/24 directly connected, GigabitEthernet0/0Interaction with Other Protocols
RIPv2 can be redistributed into other routing protocols (OSPF, EIGRP) and vice versa. It uses administrative distance 120, so it is less preferred than connected (0), static (1), EIGRP (90/170), or OSPF (110). RIPv2 does not support authentication by default but can be configured with plaintext or MD5 authentication using key chains.
Enable RIP routing process
Enter global configuration mode and use the `router rip` command to start the RIP process. This creates a RIP routing process on the router. Note that RIP is not enabled by default; you must explicitly configure it. After this command, the prompt changes to `config-router`.
Specify RIPv2 as the version
By default, Cisco IOS runs RIPv1 (which sends broadcasts and does not include subnet masks). Use `version 2` to enable RIPv2. This changes updates to multicast 224.0.0.9 and includes subnet masks. You can also use `version 1` or leave it unset (version 1). For CCNA, always use version 2.
Advertise directly connected networks
Use the `network` command followed by the classful network address of each directly connected interface. For example, `network 10.0.0.0` enables RIP on all interfaces with an IP address in the 10.0.0.0/8 range. RIP will then advertise the specific subnets. Note: The network command uses classful boundaries; you cannot specify a subnet mask here.
Disable auto-summary (if needed)
RIPv2 supports VLSM and CIDR, but by default, it summarizes routes at classful boundaries. Use `no auto-summary` to prevent this. Without this command, subnets like 10.1.1.0/24 and 10.2.1.0/24 would be summarized as 10.0.0.0/8 in updates, causing routing issues in discontiguous networks.
Verify RIP configuration
Use `show ip protocols` to confirm RIP is running, version 2 is active, timers are correct, and which interfaces are participating. Use `show ip route` to see RIP-learned routes (marked with 'R'). Use `show ip rip database` to view the RIP-specific database. Also use `debug ip rip` (in privileged exec mode) to see real-time updates for troubleshooting.
RIPv2 is rarely deployed in greenfield enterprise networks today, but it still appears in several scenarios. First, in small branch offices with limited IT staff, RIPv2 can be a simple, easy-to-configure routing protocol that requires minimal maintenance. For example, a company with three small offices connected via point-to-point links might use RIPv2 because the network has fewer than 15 hops and does not need fast convergence. The network engineer would configure RIPv2 on each router, advertise the directly connected LAN subnets, and set no auto-summary if there are discontiguous subnets. Second, RIPv2 is often used in labs and certification training because its simplicity makes it ideal for teaching routing concepts. Many CCNA candidates first learn routing with RIP before moving to OSPF. Third, legacy networks that were originally deployed with RIPv2 may still be in production, especially in organizations that avoid change. A network engineer might need to troubleshoot such a network or plan a migration to OSPF or EIGRP.
In production, RIPv2 has significant limitations: it converges slowly (the holddown timer is 180 seconds), has a maximum hop count of 15 (making it unsuitable for large networks), and uses periodic full-table updates that consume bandwidth. A misconfiguration like forgetting no auto-summary can cause black holes in discontiguous networks. For instance, if you have subnets 10.1.1.0/24 and 10.2.1.0/24 separated by a non-10 network, auto-summary would cause both routers to advertise 10.0.0.0/8, leading to routing loops or suboptimal paths. Another common mistake is enabling RIP on the wrong interface by using an incorrect network statement. Always verify with show ip protocols to see which interfaces are sending and receiving RIP updates.
The CCNA 200-301 exam objective 3.3 covers RIPv2, but it is a minor topic. Expect 1-2 questions, often comparing RIPv2 to other protocols or testing configuration knowledge. Here is what you must know:
RIPv2 characteristics: Uses UDP port 520, multicast 224.0.0.9, supports VLSM and CIDR, has a 15-hop limit (16 = infinity), administrative distance 120, update timer 30 seconds, invalid/holddown 180 seconds, flush 240 seconds.
Common wrong answers:
- Choosing RIPv1 over RIPv2 because of classful behavior (but exam asks for v2).
- Thinking RIP uses TCP (it uses UDP).
- Confusing the metric: RIP uses hop count, not bandwidth or delay.
- Forgetting that no auto-summary is required for discontiguous subnets.
3. Trap: The exam may show a show ip route output with a route marked 'R' and administrative distance 120. They might ask why the route is not in the table (e.g., metric 16, or route in holddown).
4. Calculation: No complex calculations, but you might need to determine if a route is reachable based on hop count (must be ≤15).
5. Decision rule: If a question involves a routing protocol that is simple, uses hop count, and is classless with VLSM, it is RIPv2. If it mentions broadcast updates or no subnet masks, it is RIPv1. For scenario questions, look for keywords like 'small network', 'legacy', or 'simple configuration'.
RIPv2 uses UDP port 520 and multicast address 224.0.0.9.
RIPv2 has a maximum hop count of 15; 16 means unreachable.
Default timers: update 30s, invalid 180s, holddown 180s, flush 240s.
Administrative distance of RIP is 120.
Use `no auto-summary` to advertise subnets without classful summarization.
Split horizon prevents routing loops by not advertising routes back out the receiving interface.
RIPv2 supports VLSM and CIDR by including subnet mask in updates.
These come up on the exam all the time. Here's how to tell them apart.
RIPv2
Uses multicast 224.0.0.9
Includes subnet mask in updates
Supports VLSM and CIDR
Supports authentication (plaintext/MD5)
Classless routing protocol
RIPv1
Uses broadcast 255.255.255.255
No subnet mask in updates
Classful routing only
No authentication
Classful routing protocol
Mistake
RIPv2 uses broadcast address 255.255.255.255 for updates.
Correct
RIPv2 uses multicast address 224.0.0.9. RIPv1 uses broadcast.
Candidates confuse v1 and v2; the multicast is a key differentiator.
Mistake
RIP automatically summarizes routes; you cannot disable it.
Correct
You can disable auto-summary with the `no auto-summary` command under router rip.
Many think auto-summary is mandatory because it is enabled by default.
Mistake
RIP uses TCP port 520 for reliable delivery.
Correct
RIP uses UDP port 520. It does not use TCP; reliability is not guaranteed by the protocol.
Candidates often assume routing protocols use TCP for reliability.
Mistake
The RIP metric is based on bandwidth and delay.
Correct
RIP uses hop count as its only metric. Each router adds 1 to the hop count.
Confusion with OSPF (cost) or EIGRP (composite metric).
Reveal each answer, then mark whether you got it right. Score 60%+ to unlock the next chapter.
RIPv2 improves on RIPv1 by supporting classless routing (VLSM and CIDR) through the inclusion of subnet masks in updates. RIPv2 uses multicast address 224.0.0.9 instead of broadcast, and it supports authentication. RIPv1 is classful and sends broadcasts. For CCNA, always use RIPv2.
Use the `no auto-summary` command under router rip. This disables automatic summarization at classful boundaries, allowing subnets to be advertised individually.
The maximum valid hop count is 15. A metric of 16 indicates an unreachable route (infinity). This limits the size of a RIP network to 15 hops.
Yes, by default RIPv2 supports equal-cost load balancing across up to 4 paths (configurable with `maximum-paths`). This is useful for redundancy.
Split horizon is a loop prevention mechanism where a router never advertises a route back out the interface from which it was learned. This prevents routing loops in simple topologies.
Use `show ip protocols` to see the routing protocol, version, timers, and interfaces. Use `show ip route` to see RIP-learned routes (marked with 'R'). Use `show ip rip database` for the RIP database.
RIP has an administrative distance of 120. This means it is less preferred than connected (0), static (1), EIGRP (90/170), or OSPF (110), but more preferred than external EIGRP (170) or BGP (20/200).
You've just covered RIPv2 Basics — now see how well it sticks with free CCNA 200-301 practice questions. Full explanations included, no account needed.
Done with this chapter?