201 · Question #159
A 8IG-IP Administrator configures a node with a standard icmp Health Monitor. The Node shows as DOWN although the Backend Server is configured to answer ICMP requests. Which step should the…
The correct answer is C. Runatcpdump. To diagnose why an ICMP health monitor reports a node as DOWN despite the backend server responding to ICMP, the administrator should run 'tcpdump'. This utility captures network traffic, allowing inspection of ICMP packets between the BIG-IP and the server to identify…
Question
A 8IG-IP Administrator configures a node with a standard icmp Health Monitor. The Node shows as DOWN although the Backend Server is configured to answer ICMP requests. Which step should the administrator take next to find the root cause of this issue?
Options
- ARun a curl Run a qkview
- BRun a qkview
- CRunatcpdump
- DRunanssldump
How the community answered
(60 responses)- A12% (7)
- B7% (4)
- C78% (47)
- D3% (2)
Why each option
To diagnose why an ICMP health monitor reports a node as DOWN despite the backend server responding to ICMP, the administrator should run 'tcpdump'. This utility captures network traffic, allowing inspection of ICMP packets between the BIG-IP and the server to identify connectivity or routing issues.
'curl' is used for making HTTP/HTTPS requests and is irrelevant for diagnosing ICMP connectivity issues; 'qkview' collects system diagnostic information but does not provide real-time packet-level insight into a specific ICMP health check failure.
'qkview' collects comprehensive system diagnostic information, which is useful for F5 Support, but it does not provide the real-time, granular packet-level view necessary to debug a specific live ICMP communication failure.
'tcpdump' is a command-line packet analyzer used to capture and display network packets. Running 'tcpdump' on the BIG-IP device while the health monitor is active will show if ICMP requests are being sent to the server, if replies are being received, and if any network devices are blocking or altering the traffic, thus pinpointing the communication failure.
'ssldump' is used for analyzing SSL/TLS encrypted traffic, which is not applicable to a standard ICMP health monitor as ICMP is an unencrypted Layer 3 protocol.
Concept tested: Troubleshooting BIG-IP health monitor with tcpdump
Source: https://support.f5.com/csp/article/K411
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