Sometimes attaching a device to a DrayTek router may appear to be not correctly connected to the network.

In the SysLog you may see a number of entries referring to ARP MISMATCH or INVALID ARP.  

This indicates that invalid ARP packets are being blocked by the router.  Be aware that this is an issue with whatever device is connecting to the router and sending invalid packets. 

The router is doing its job by blocking illegal ARP messages. However, this is not ideal if you want to ignore those bad packets and allow the new device to access your network.

To resolve this issue and allow invalid ARP packets through the router, telnet to the router and execute the following command to allow illegal source MAC address;

ip arp accept 1

If the issue persists you may also need to allow illegal destination MAC address and / or allow VRRP MAC entries into the ARP table with the following commands;

ip arp accept 3

ip arp accept 5

To see the status of the ARP accept rules use this command;

ip arp accept status

Make sure that the settings are stored by using the sys commit command

sys commit

Here is a sample of what the commands look like.