Troubleshooting Methods Flashcards

Which Junos command captures live packet data on an interface for analysis?

Answer: monitor traffic interface ge-0/0/0

The 'monitor traffic interface' command in Junos operational mode captures and displays live packet headers (similar to tcpdump) on the specified interface for real-time troubleshooting.

What does 'show interfaces ge-0/0/0 extensive' display that 'show interfaces ge-0/0/0' does not?

Answer: Detailed error counters including input/output errors, drops, framing errors, and CoS queue statistics

The 'extensive' keyword adds granular error counters (CRC errors, giants, runts, drops), CoS queue statistics, active alarms, and detailed physical layer information to the standard interface output.

In Junos, how do you trace the path a packet takes through the network?

Answer: traceroute [destination]

The 'traceroute' command in Junos operational mode sends probes with increasing TTL values to discover each hop between the local router and the destination.

What is the purpose of Junos 'traceoptions' in protocol configuration?

Answer: Enables detailed debug logging for specific protocols to a file for troubleshooting

Traceoptions in Junos configuration enables protocol-level debug logging (e.g., OSPF packet exchange, BGP UPDATE messages) to a specified file in /var/log/ for detailed troubleshooting.

Which command in Junos shows the status of all BGP peers?

Answer: show bgp summary

'show bgp summary' provides a concise table of all BGP neighbors with their state (Established, Active, Idle), received prefixes, and uptime — the fastest way to assess BGP health.

What does a 'martian' route mean in Junos troubleshooting context?

Answer: A route that Junos refuses to install because the destination is a reserved or invalid address (e.g., 0.0.0.0/0, 127.x.x.x)

Martian routes are addresses that should never appear as routable destinations (loopback, link-local, broadcast, multicast used as unicast destinations). Junos drops these to prevent routing anomalies.