ARP table issues can lead to network connectivity problems, packet loss, slow performance, or even security vulnerabilities like ARP spoofing. This step-by-step guide will help you identify and fix ARP table issues by clearing and updating the ARP cache to restore proper network. What can cause incomplete arp table for a fast ethernet connection on a cisco router? If the device connected to the cisco is connected but power off or in standby, would cisco issue an incomplete arp or would it remove the arp from the table completely? Thanks 10-13-2007 05:20 PM Dan Perhaps there. What are the reasons for seeing an incomplete ARP? As was mentioned in this post: The reason for seeing an incomplete ARP is that "An ARP request was sent for that address, but the host with that address is not up and running on the LAN, so there is no reply" So, if a multilayer switch sends an ARP. The Address Resolution Protocol (ARP) is essential for mapping IP addresses to MAC addresses, enabling seamless communication in a local network. This. If the MAC ADDRESS field of an ARP entry in the display arp command output displays Incomplete, the ARP entry is temporary. When IP packets trigger ARP Miss messages, the switch generates temporary ARP entries based on the ARP Miss messages, and sends ARP request packets to the destination network. At a rough guess this is a vlan issue. The arp table shows multiple subnets attached to vlan 20. it also shows IP addresses in vlan 20 that match your gig0/0 routed interface - which should not be possible. Is the firewall directly connected to gi0/0 ? Gi0/2 is showing as using vlan 1 but it seems. Incorrect or out-of-date entries in the ARP table can cause network issues.