HowTo: Understanding a packet header

Let's take a look at some of the packets we already know and understand. First of a few basics as a reminder:

1. each and every packet has a header and a body
2. the header is fixed size, the body is variable in size
3. the header is fixed in content, the body varies

For now let's focus on what we know about the header.

Bytes	Description	Length
0x00-0x01	The session ID. The server and the client each have a session ID.	2
0x02-0x03	The length of the packets body in bytes	2
0x04-0x07	The command (aka action aka OP code) this packet will perform	4
0x08-0x0B	The sequence number of the packet (necessary for ordering UDP packets)	4
0x0C-0x0F	The checksum of the packets body	4
0x10-0x11	Packet group number (e.g. 0xffeb, confirmed in the 08004002 packet)	4
0x12-0x13	Unclear, get increased by the server	4