network [classful-network]
Enables RIP routing on a classful network, causing the router to advertise and learn routes for that network via RIP updates.
Definition: network [classful-network] is a Cisco IOS router config command. Enables RIP routing on a classful network, causing the router to advertise and learn routes for that network via RIP updates.
Overview
The `network` command under router configuration mode for RIP is used to enable RIP routing on a classful network. This command tells the router to advertise the specified classful network via RIP updates and to listen for RIP updates on interfaces that belong to that network. RIP is a distance-vector routing protocol that uses hop count as its metric, with a maximum of 15 hops.
The `network` command is essential for including interfaces in the RIP routing process; without it, the router will not send or receive RIP updates on any interface. This command is typically used in small to medium-sized networks where simplicity is key, and where the network topology is not too complex. Alternatives include EIGRP or OSPF for larger, more scalable networks.
In the configuration workflow, after enabling RIP with `router rip`, you use the `network` command to specify which directly connected networks should participate in RIP. The command operates on classful boundaries, meaning that if you specify a subnet, it will be automatically converted to its classful network. For example, `network 10.1.1.0` becomes `network 10.0.0.0`.
This behavior can lead to unintended advertisements if you have discontiguous subnets. The command is executed in router configuration mode, which requires privileged EXEC access (enable mode). It modifies the running configuration immediately.
Understanding this command is fundamental for CCNA and CCNP candidates as it forms the basis of RIP configuration and troubleshooting.
network [classful-network]When to Use This Command
- Enabling RIP on a directly connected classful network to participate in dynamic routing.
- Adding a new network to an existing RIP configuration to propagate its routes.
- Configuring RIP on a stub network to advertise its local subnet to upstream routers.
- Re-enabling RIP on a network after removing it with 'no network' command.
Parameters
| Parameter | Syntax | Description |
|---|---|---|
| classful-network | A.B.C.D | The classful network address (e.g., 10.0.0.0, 172.16.0.0, 192.168.1.0) to enable RIP on. The router will include all interfaces that have an IP address belonging to this classful network. Common mistake: using a subnet mask or a host address; the command automatically converts to classful, which may cause unexpected behavior. |
Command Examples
Enabling RIP on a Classful Network
network 192.168.1.0Router(config-router)# network 192.168.1.0 Router(config-router)#
The command is entered without any output confirmation. It enables RIP on the classful network 192.168.1.0, which includes all interfaces with an IP address in that range.
Enabling RIP on Multiple Networks
network 10.0.0.0
network 172.16.0.0Router(config-router)# network 10.0.0.0 Router(config-router)# network 172.16.0.0 Router(config-router)#
Multiple network statements can be added. Each enables RIP on the respective classful network. The router will advertise and learn routes for all subnets within these classful networks.
Understanding the Output
The 'network' command does not produce any immediate output. It silently adds the specified classful network to the RIP process. To verify, use 'show ip protocols' or 'show run | section router rip'.
In 'show ip protocols', look for 'Routing for Networks:' listing the classful networks. In 'show run', the network statements appear under 'router rip'. A missing network means RIP is not active on that network.
Ensure the network is classful (e.g., 192.168.1.0, not 192.168.1.128) and that interfaces have IP addresses within that range.
Configuration Scenarios
Enable RIP on a single classful network
A small office with one router (R1) connected to the 192.168.1.0/24 LAN. The goal is to enable RIP so that R1 advertises this network to neighboring routers.
Topology
R1(Gi0/0)---192.168.1.0/24---PCSteps
- 1.Step 1: Enter privileged EXEC mode: enable
- 2.Step 2: Enter global configuration mode: configure terminal
- 3.Step 3: Enter RIP router configuration mode: router rip
- 4.Step 4: Enable RIP on the classful network: network 192.168.1.0
- 5.Step 5: Exit configuration mode: end
- 6.Step 6: Verify the configuration: show ip protocols
! R1# configure terminal R1(config)# router rip R1(config-router)# network 192.168.1.0 R1(config-router)# end R1#
Verify: Use `show ip protocols` to verify that RIP is running and that the network 192.168.1.0 is listed under 'Routing for Networks'. Expected output includes 'Routing Protocol is "rip"' and 'Routing for Networks: 192.168.1.0'.
Watch out: If the interface IP is 192.168.1.1/24, the command `network 192.168.1.0` works. But if you mistakenly type `network 192.168.1.1`, the router will still convert it to 192.168.1.0, which is fine. However, if you have a discontiguous subnet like 192.168.2.0/24 on another interface, it will not be advertised unless you add another `network` statement.
Enable RIP on multiple classful networks with passive interface
A router (R2) connects two classful networks: 10.0.0.0/8 and 172.16.0.0/16. The goal is to advertise both networks via RIP, but suppress RIP updates on the 10.0.0.0 interface to prevent unnecessary broadcasts.
Topology
R2(Gi0/0)---10.0.0.0/8---R1
R2(Gi0/1)---172.16.0.0/16---R3Steps
- 1.Step 1: Enter privileged EXEC mode: enable
- 2.Step 2: Enter global configuration mode: configure terminal
- 3.Step 3: Enter RIP router configuration mode: router rip
- 4.Step 4: Enable RIP on network 10.0.0.0: network 10.0.0.0
- 5.Step 5: Enable RIP on network 172.16.0.0: network 172.16.0.0
- 6.Step 6: Set Gi0/0 as passive interface: passive-interface GigabitEthernet0/0
- 7.Step 7: Exit configuration mode: end
- 8.Step 8: Verify: show ip protocols and show ip rip database
! R2# configure terminal R2(config)# router rip R2(config-router)# network 10.0.0.0 R2(config-router)# network 172.16.0.0 R2(config-router)# passive-interface GigabitEthernet0/0 R2(config-router)# end R2#
Verify: `show ip protocols` should list both networks under 'Routing for Networks'. `show ip rip database` should show routes learned via RIP. To confirm passive interface, use `show ip interface Gi0/0` and look for 'RIP passive interface' or use `show running-config | section router rip`.
Watch out: If you forget to add the `passive-interface` command, the router will send RIP broadcasts out of Gi0/0, which may be unnecessary or cause security issues. Also, note that the `network` command uses classful boundaries; if you have subnets like 10.1.0.0/16 and 10.2.0.0/16, both are covered by `network 10.0.0.0`.
Troubleshooting with This Command
When troubleshooting RIP, the `network` command is often the first place to check. A common issue is that RIP is not advertising or learning routes because the `network` statement is missing or incorrect. Start by verifying that RIP is enabled on the router with `show ip protocols`.
This command displays the routing protocol, its timers, and the networks it is routing for. If the expected network is not listed, you need to add the `network` command. Another useful command is `show ip rip database`, which shows the RIP routing table.
If you see routes, but they are not being advertised, check if the interface is passive or if there is an access list blocking RIP (UDP port 520). Use `debug ip rip` to see real-time updates; this will show which networks are being sent and received. Look for 'RIP: sending v1 update to 255.255.255.255 via GigabitEthernet0/0' and verify that the network you configured appears in the update.
If you see 'RIP: ignored v1 update from ...' it may indicate a version mismatch or authentication issue. Also, check the interface configuration: the interface must have an IP address in the classful network and be up/up. Use `show ip interface brief` to verify.
If you have discontiguous subnets, remember that RIP automatically summarizes to classful boundaries. This can cause routing black holes if you have subnets of the same classful network separated by another network. To avoid this, you can disable auto-summary with `no auto-summary` under router rip.
In summary, the troubleshooting flow is: 1) Verify RIP is running and networks are configured with `show ip protocols`. 2) Check the RIP database with `show ip rip database`. 3) Use `debug ip rip` to see updates. 4) Verify interface status and IP addressing. 5) Check for passive interfaces or filters. Correlate the output of these commands to isolate the issue.
CCNA Exam Tips
CCNA exam expects you to know that the 'network' command uses classful networks only; using a subnet mask is invalid.
Remember that RIP version 1 is classful and does not support VLSM; the network command must match the classful boundary.
The 'network' command enables RIP on all interfaces belonging to that classful network; you cannot selectively enable RIP on a single interface.
In RIP version 2, the network command still uses classful networks, but VLSM is supported via subnet masks in updates.
Common Mistakes
Using a subnet mask with the network command (e.g., 'network 192.168.1.0 0.0.0.255') — this is invalid and will be rejected.
Forgetting to enter router configuration mode before issuing the command, resulting in 'Invalid input detected'.
Typing a host address instead of a network address (e.g., 'network 192.168.1.1') — this will be interpreted as the classful network 192.168.1.0, but it's better practice to use the network address.
network [classful-network] vs router rip
The commands 'router rip' and 'network [classful-network]' are commonly confused because both are required to configure RIP but serve different purposes: 'router rip' enters the RIP configuration mode, while 'network' specifies which directly connected networks will be advertised via RIP. Understanding their distinct roles is crucial for proper RIP setup.
| Aspect | network [classful-network] | router rip |
|---|---|---|
| Scope | Applies to a specific classful network for RIP updates | Enables the RIP routing process globally |
| Configuration mode | Subcommand under router rip configuration mode | Global configuration mode |
| Persistence | Saved as a network statement under router rip in running-config | Saved as router rip process definition in running-config |
| Precedence | Requires 'router rip' to be configured first | Must be issued before any RIP subcommands |
| Typical use | Advertise a directly connected network via RIP | Initiate RIP configuration and enter router config mode |
Use network [classful-network] when you want to enable RIP on interfaces belonging to that classful network, causing them to send and receive RIP updates.
Use router rip when you need to enter RIP router configuration mode to enable the RIP routing process and access subcommands like 'network' and 'version'.
Platform Notes
In IOS-XE (e.g., 16.x), the `network` command syntax and behavior are identical to classic IOS. However, IOS-XE may have additional features like RIPng for IPv6, but the IPv4 RIP `network` command remains unchanged. In NX-OS (e.g., Nexus switches), RIP is not supported; instead, use EIGRP or OSPF.
For ASA firewalls, RIP is not typically used; they support OSPF, EIGRP, and static routes. In IOS-XR (e.g., ASR 9000), RIP is not supported; the equivalent would be OSPF or IS-IS. For IOS versions, the `network` command has been consistent from 12.x to 15.x to 16.x.
One difference: in older IOS (12.x), the default RIP version is version 1, while in newer IOS (15.x+), it may default to version 2. This does not affect the `network` command syntax. Always check the version with `show version`.
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