500-230 Sample Questions & Answers

This statement is false. In IOS-XR's two-stage configuration model, changes made in configuration mode are held in a target or 'scratchpad' configuration. They are not applied to the active running configuration, nor are they synchronized to the standby RP, until the commit command is executed. The commit operation is what validates the changes, applies them to the active RP, and then synchronizes the new running configuration to the standby RP.

Inter-AS Option C's main characteristic is that it extends the MPLS LSP from the ingress PE in one AS to the egress PE in another AS. To achieve this, the PE loopback addresses must be reachable across AS boundaries. This is accomplished by exchanging these loopbacks as labeled-unicast routes between the ASBRs (e.g., using address-family ipv4 labeled-unicast). This allows the PEs to build a recursive LSP to the remote PE's next-hop. Redistributing into the IGP would be a massive scalability and security issue.

In IOS-XR, the install add source test command is specifically designed for pre-installation checks. It performs a dry run of the installation process, which includes verifying the package's integrity, checking for dependencies and prerequisites, and ensuring there are no conflicts, all without making any changes to the system. This is a critical best practice before applying any software update to a production device.

When a process like BGP shows high CPU usage, it's often a single thread within that process causing the issue. The show processes detail command is the best first step as it breaks down the process into its individual threads and shows the CPU time consumed by each. This allows the engineer to pinpoint the specific function (e.g., scanner, router, I/O) that is misbehaving, which is essential for targeted debugging. Restarting the process is a last resort, and simply confirming the high usage doesn't provide new diagnostic data.

The configure exclusive command provides a system-wide lock, preventing any other user from entering configuration mode until the current user exits. The lock command is less restrictive; it is issued from within an existing configuration session and allows other users to enter configuration mode and make changes in their own sessions, but it prevents anyone from committing their changes until the lock is released.

A 'No Label' entry in the LFIB indicates that the router has no outgoing label for the prefix. This is the expected behavior for the Egress Label Switched Router (LSR) when Penultimate Hop Popping (PHP) is active (which it is by default). The egress router does not need to forward the packet with a label; instead, it pops the final label and performs an IP lookup to forward the native IP packet to its destination. The Penultimate Hop router would show an 'Implicit-Null' or 'Pop' label, not 'No Label'.

While Stateful Switchover (SSO) ensures the standby RP is ready to take over control plane functions, it does not inherently preserve routing protocol adjacencies. Non-Stop Routing (NSR) is the feature that works with SSO to synchronize routing protocol state information between the active and standby RPs. With NSR enabled, peers do not see the RP switchover, and adjacencies are maintained, preventing a routing reconvergence and the associated traffic loss.

To track which user issues which commands, AAA (Authentication, Authorization, and Accounting) must be implemented. Specifically, the 'Accounting' component is responsible for logging actions. By configuring accounting commands to send logs to a TACACS+ or RADIUS server, every command entered (including configuration changes and commits) is logged along with the authenticated username, providing a clear audit trail.

The copy running-config tftp: command is the standard and direct method on IOS-XR (and classic IOS) to copy the currently active configuration from the router's memory to a remote TFTP server. The system will then prompt for the IP address of the TFTP server and the destination filename.

The show memory-leaks command is a powerful, specialized tool in IOS-XR designed specifically for tracking down memory leaks. When used with the process keyword, it allows an engineer to monitor memory allocations within a specific process over time. The system takes snapshots of memory usage and can report on memory blocks that are allocated but never freed, which is the definition of a leak. This is far more effective than general memory commands for this specific troubleshooting task.