A practical network troubleshooting method
A repeatable troubleshooting method starts with a precise symptom and ends with a verified outcome.
Define the flow
Write down the source, destination, direction, protocol, and port. A successful ICMP probe does not establish that HTTPS is permitted. Use the same flow the user reports.
Locate the first unexpected decision
Compare a packet trace with the routing table at the failing hop. A route may point to a discard interface, return traffic may lack a route, or a filter may block a permitted service.
Verify the fix and the boundaries
Retest the reported service in both directions. Then check a flow that should still be blocked. Removing an access list can restore connectivity while creating a new exposure.
Protocol reference: IPv4 router forwarding requirements — RFC 1812.
Green links. Broken checkout.
Chicago payments network. Four routed metro nodes form a ring; the service gateway has a separate handoff. Route checks and ICMP succeed. The primary service transport fails even though an allow rule appears in the service access list. Investigate the two service networks from R2: 10.201.130.0/24 to 10.201.136.0/24 (TCP/443), and 10.201.131.0/24 to 10.201.137.0/24 (TCP/8443).
Link addressing (5)
- R1 R2
10.201.144.0/30 - R2 R3
10.201.145.0/30 - R3 R4
10.201.146.0/30 - R4 R1
10.201.147.0/30 - R4 R5
10.201.148.0/30
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