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What information about a Cisco router can be verified using the show version command?

• the routing protocol version that is enabled
• the value of the configuration register
• the operational status of serial interfaces
• the administrative distance used to reach networks

The correct answer is “the value of the configuration register.”

The show version command on a Cisco router is a powerful tool that provides crucial information about the router’s software and hardware status. When you execute this command, you gain insight into various aspects of the router’s configuration, including software version, uptime, hardware details, and the value of the configuration register. However, it is essential to understand that not all the options listed in your question are verifiable using this command. Let’s delve into each aspect to clarify what the show version command actually reveals, and which of the listed options it can or cannot verify.

1. Routing Protocol Version Enabled

The show version command does not provide information about the specific routing protocols (such as OSPF, EIGRP, or BGP) or their versions that are enabled on the router. Instead, the show version command focuses on the overall system and hardware status. If you want to verify which routing protocols are enabled and their versions, you would typically use other commands like show ip protocols, show running-config, or specific protocol-related commands like show ip ospf or show ip eigrp.

For instance, to verify the version of OSPF that is running on the router, you would use the show ip ospf command. This would provide detailed information about the OSPF process, including its version. Therefore, the show version command is not useful for verifying the routing protocol version.

2. The Value of the Configuration Register

One of the key pieces of information provided by the show version command is the value of the configuration register. The configuration register is a 16-bit value stored in NVRAM that determines how the router boots. It controls several boot functions, including whether the router boots into ROMMON (ROM Monitor) mode or from flash memory, and whether it loads a configuration file from NVRAM.

Typically, the configuration register is set to 0x2102, which tells the router to boot from flash memory and load the configuration file from NVRAM. However, this value can be changed to perform different tasks. For example:

• 0x2142 bypasses the startup configuration in NVRAM during boot, which is useful for password recovery.
• 0x2101 tells the router to boot from the first available image in flash.

To see the current configuration register value, you would look for a line in the output of show version that says something like:

Configuration register is 0x2102

This line indicates the configuration register value the router will use upon the next reload or reboot.

3. The Operational Status of Serial Interfaces

The show version command does not provide detailed information about the operational status of specific interfaces, such as serial interfaces. While show version may display general information about the hardware, including the number and type of interfaces available on the router, it does not delve into their operational status, such as whether an interface is up or down.

To check the status of serial interfaces or any other interface on a Cisco router, you would use commands like show interfaces, show ip interface brief, or show controllers serial. These commands provide detailed output about the line status, protocol status, input/output errors, and many other interface-specific details.

For example, show ip interface brief provides a concise summary of the status of all interfaces:

Interface           IP-Address        OK?  Method  Status         Protocol
FastEthernet0/0     192.168.1.1       YES  manual  up             up
Serial0/0           10.1.1.1          YES  manual  up             up

This output shows whether each interface is “up” or “down,” both in terms of the physical link and the data link layer protocol.

4. The Administrative Distance Used to Reach Networks

The show version command does not display information about the administrative distance used by the router to reach networks. Administrative distance is a value used by routers to select the best path when multiple routes to the same destination are learned via different routing protocols. The lower the administrative distance, the more preferred the route.

To verify the administrative distance values, you would use commands like show ip route. This command provides a detailed view of the routing table, including the administrative distance for each route. For example:

Gateway of last resort is 0.0.0.0 to network 0.0.0.0

     10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
C      10.1.1.0/24 is directly connected, FastEthernet0/0
D      10.2.2.0/24 [90/2172416] via 10.1.1.2, 00:00:03, Serial0/0
R      10.3.3.0/24 [120/1] via 10.1.1.3, 00:00:04, Serial0/1

In this example, C indicates a connected route, which has an administrative distance of 0. D indicates a route learned via EIGRP, with an administrative distance of 90, and R indicates a route learned via RIP, with an administrative distance of 120.

Additional Information Provided by show version

Besides the configuration register, the show version command also provides several other critical pieces of information:

• IOS Version: It displays the version of the Cisco Internetwork Operating System (IOS) that the router is running. This is vital for ensuring compatibility with other devices and understanding the features available on the router.
• Uptime: The command shows how long the router has been running since the last reboot, which can help in diagnosing stability issues.
• System Image: It provides information about the file used to boot the router, including the filename and the location (e.g., flash memory).
• Hardware Details: This includes the amount of memory (RAM and Flash), the number of interfaces, the type of processor, and the router model.
• License Information: On newer IOS versions, show version might also display license details, including the features and services enabled.
• ROM Version: The command displays the ROM version, which is essential for understanding the low-level firmware the router uses during the boot process.
• Router Serial Number and Model: These details are crucial for inventory management, warranty checks, and support cases with Cisco.

Conclusion

The show version command is indispensable for network administrators managing Cisco routers, as it provides essential details about the system’s hardware and software configuration. However, it does not provide information about routing protocols, interface statuses, or administrative distances. These details require other specialized commands like show ip protocols, show interfaces, and show ip route.

Understanding what the show version command can and cannot do helps administrators quickly find the information they need and understand when to use other commands for more specific queries. This knowledge is vital for effective network management and troubleshooting, ensuring that routers are running the correct software versions, booting properly, and configured correctly for the intended network environment.