AR18-22-24 E1/0 connects external network and enables NAT. IP address of E 3/0 (L3 interface) is the gateway of private network. E 3/0 connects L2 switch and the switch attaches PC.
Parts of PC users cannot access network. Change users’ IP address and they can access network.
Check attack source and troubleshoot it. The problem is solved.
Check ARP entry of the router. For the users cannot access network, their MAC is 0000-0000-0001, 0000-0000-0002. These MAC address does not match users’actual MAC.
There is ARP attack in LAN.