When you install a firewall or make configuration changes to one, you might need to verify that it can communicate on all its interfaces. Users might also report problems they experience when trying to pass through the firewall. You need a logical approach to verifying the firewall's operation and troubleshooting its connectivity.
You can follow these basic steps to verify that a firewall can communicate with its neighboring networks:
Test with ping packets.
Check the ARP cache.
Check the routing table.
Use traceroute from a workstation to verify the forwarding path through the firewall.
Check the access lists.
Verify address translation operation.
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