There are no 56 option in the DHCP NAK packet, that is, there is no message about the error that occurred according to rfc2131 / rfc2132. There is also mention of the use of 54 option, which is also not in the DHCP NAK packet. As a consequence, SOHO routers of some manufacturers ignore DHCP NAK from accel.
This option is used by a DHCP server to provide an error message to a DHCP client in a DHCPNAK message in the event of a failure. A client may use this option in a DHCPDECLINE message to indicate the why the client declined the offered parameters. The message consists of n octets of NVT ASCII text, which the client may display on an available output device. The code for this option is 56 and its minimum length is 1. Code Len Text +-----+-----+-----+-----+--- | 56 | n | c1 | c2 | ... +-----+-----+-----+-----+---