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Questions: Proxy ARP Causing Unexpected Routing Behavior

  • Is proxy ARP enabled on the router's interfaces (check ip proxy-arp or equivalent)?
  • What does the ARP table on the affected hosts show for remote subnet IPs?
  • Does the MAC address for remote IPs in the ARP table match the router's interface MAC?
  • What does traceroute show for the path between hosts on different subnets?
  • Are there ACLs or firewall rules that should be blocking this cross-subnet traffic?
  • What is the subnet mask configured on the hosts -- could a misconfigured mask cause ARP for remote IPs?
  • Was proxy ARP intentionally enabled for a specific purpose, or is it a default?
  • Does disabling proxy ARP on the router break any legitimate functionality?
  • Are hosts configured with a proper default gateway?