Grading Checklist: Proxy ARP Causing Unexpected Routing Behavior

• Identified proxy ARP as the mechanism allowing cross-subnet communication
• Explained how proxy ARP works: router responds to ARP requests for IPs on other connected subnets
• Checked router interface configuration for ip proxy-arp setting
• Examined host ARP tables and identified router MAC for remote IPs
• Noted that traceroute appears as one hop because ARP resolution is "local"
• Explained the security implications of proxy ARP bypassing subnet segmentation
• Proposed disabling proxy ARP: no ip proxy-arp on router interfaces
• Warned that disabling proxy ARP may break hosts without a default gateway configured
• Verified that all hosts have correct default gateway settings before disabling
• Mentioned that proxy ARP is enabled by default on many Cisco platforms
• Discussed alternative scenarios where proxy ARP is legitimate (e.g., DHCP relay, unnumbered interfaces)
• Recommended flushing ARP caches on hosts after disabling proxy ARP