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Difficulty: MediumTroubleshooting Routing, Default Gateways, and ACLs

A network technician is troubleshooting a connectivity issue where hosts on VLAN 20 (192.168.20.0/24192.168.20.0/24) are unable to access an enterprise application server at 10.100.50.2510.100.50.25. Place the following diagnostic and remediation steps in the correct order according to standard CompTIA network troubleshooting methodology, from first step to last step.

  1. 1Ping the local default gateway interface (192.168.20.1192.168.20.1) from a VLAN 20 workstation to verify local Layer 3 reachability.
  2. 2Execute a traceroute command to 10.100.50.2510.100.50.25 to pinpoint the intermediate router hop where traffic stops advancing.
  3. 3Inspect the IP routing table on the identified router to confirm a valid static or dynamic route to destination subnet 10.100.50.0/2410.100.50.0/24 exists.
  4. 4Review ingress and egress Access Control Lists (ACLs) on the router interface to check for misconfigured rules or an implicit deny statement blocking traffic.
  5. 5Modify the routing table or ACL rule configuration, then test reachability to 10.100.50.2510.100.50.25 to verify full end-to-end functionality.

Answer

The correct troubleshooting order begins with testing local gateway reachability, followed by using traceroute to locate the failing hop, inspecting the routing table at that hop, reviewing ACL rules on the interface, and finally implementing the fix to verify restored connectivity.
Network troubleshooting follows a logical divide-and-conquer path: verify local gateway access first, trace the path to locate the failure hop, verify routing table entries at that hop, audit interface ACL policies, and conclude by executing the fix and verifying full end-to-end application access.

Step-by-Step Solution

1
Ping the local default gateway (192.168.20.1192.168.20.1)
Confirms local network link and IP configuration on the client workstation are working.
Troubleshooting should always begin at the local segment before analyzing remote network infrastructure.
2
Run traceroute to target IP 10.100.50.2510.100.50.25
Identifies the exact intermediate router where packet forwarding ceases.
Traceroute narrows down the problem area across a multi-hop routed infrastructure.
3
Check the routing table on the target router
Verifies if the router possesses an active next-hop route to 10.100.50.0/2410.100.50.0/24.
Unroutable traffic is immediately dropped by routers lacking a matching route entry.
4
Examine interface ACL configurations
Identifies any explicit deny statements or implicit deny rules dropping packets on the active path.
Security filters override routing logic when configured to drop specific source/destination traffic.
5
Apply resolution and perform end-to-end verification
Restores full communication between VLAN 20 hosts and 10.100.50.2510.100.50.25.
Standard methodology requires verifying full system functionality after implementing a fix.

Key Concept

Methodological troubleshooting of routed networks by isolating issues from local gateway reachability to path routing tables and ACL security filters.
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Topics

Troubleshooting Routing, Default Gateways, and ACLs

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