Devices that process datagrams may not be able to forward a datagram due to some type of error in the header. This error does not relate to the state of the destination host or network but still prevents the datagram from being processed and delivered. In this case, an ICMP type 12 parameter problem message is sent to the source of the datagram. Figure shows the parameter problem message header.

The parameter problem message includes the pointer field in the header. When the code value is 0, the pointer field indicates the octet of the datagram that produced the error.