+
20040101 - Simple IP Reference
+
+
________________________________________________________________
+
+ SIMPLE IP REFERENCE - USE RFC'S FOR FULL REFERENCE
+
+
+ This is a minimal reference for programming a simple operating
+ system's internet related code. Note network byte order is big
+ endian (most significant byte first), keep this in mind when
+ sending multibyte sized numbers. This assumes some basic
+ knowledge of IP networking, and is not a complete reference.
+
+________________________________________________________________
+SMTP - SIMPLE MAIL TRANSPORT PROTOCOL
+
+ In progress...
+
+
+________________________________________________________________
+POP3 - POST OFFICE PROTOCOL
+
+ Access a maildrop via TCP port 110. The following are used to
+ describe,
+
+ [optional] -> optional arguments
+ (grouping) -> used only to describe repeating
+ ... -> repeats last grouping
+ -> decimal 32
+ -> decimal 46
+ -> decimal
+ -> decimal
+ "text" -> text to be sent as is
+
+ The formatting is as follows,
+
+ client sends: (command)...
+ command: keyword [( argument)...]
+ keywords: are 3-4 characters long and case insensitive
+ arguments: are up to 40 characters long
+
+ server sends: (responce)...
+ responce: first [(extra)... ]
+ first: status_indicator keyword
+ [(
+ extra: data
+ first: may be up to 512 characters long
+ status_indicator: will be "+OK" or "-ERR"
+ always in upper case
+ data: if first character is then it
+ will actually be
+
+ The connection happens in states,
+
+ client: connects to server
+ server: "+OK" SPACE "POP3" safe_to_ignore_data
+
+ AUTHORIZATION STATE
+ The client needs to identify itself before accessing mail.
+
+ client: "USER" name
+ server: responds if good, "+OK" safe_to_ignore_data
+ server: responds if bad, "-ERR" safe_to_ignore_data
+
+ then,
+
+ client: "PASS" password
+ server: responds if good, "+OK" safe_to_ignore_data
+ server: responds if bad, "-ERR" safe_to_ignore_data
+
+ loop if bad
+
+ TRANSACTION STATE
+ In this state the mailbox is locked, all messages get
+ assigned a decimal number starting with "1" and going in
+ incremental order. All messages are flagged as not deleted.
+
+ client: "STAT"
+ server: "+OK" number_of_messages
+ mail_size_in_bytes safe_to_ignore_data
+ server: responds if bad, "-ERR" safe_to_ignore_data
+ server: does not count deleted messages in the total
+
+ client: "LIST" [ message_number]
+ server: for message_number option,
+ "+OK" size_of_message safe_to_ignore_data
+
+ server: otherwise gives multiline responce,
+ "+OK" safe_to_ignore_data
+ [(message_number message_size safe_to_ignore
+ )...]
+ server: responds if bad, "-ERR" safe_to_ignore_data
+ server: does not list deleted messages
+
+ client: "RETR" message_number
+ server: "+OK" safe_to_ignore
+ lines_of_message_remember_special_dot_dot_encoding
+
+ server: responds if bad,
+ "-ERR" safe_to_ignore_data
+ server: should not send a deleted message
+
+ client: "DELE" message_number
+ server: marks message as deleted,
+ "+OK" safe_to_ignore
+ server: responds if bad,
+ "-ERR" safe_to_ignore_data
+ server: will respond in error if already deleted
+ server: does not actualy delete message until update state
+
+ client: "NOOP"
+ server: "+OK"
+
+ client: "RSET"
+ server: messages set not deleted,
+ "+OK" safe_to_ignore
+ server: responds if bad, "-ERR"
+ safe_to_ignore_data
+
+ client: "QUIT"
+ server: changes to update state
+
+ UPDATE STATE
+ server: "+OK" safe_to_ignore_data
+ server: responds if bad, "-ERR"
+ safe_to_ignore_data
+ server: will perminatly delete messages marked as deleted
+
+ Reported email message size may be different than actual sent
+ size of message, the characters should not be counted
+ twice even though they are sent that way.
+
+
+________________________________________________________________
+SLIP - SERIAL LINE IP
+
+ Use 1006 byte datagrams (not including the adjusted characters
+ below). To send a packet just send data. If data byte is 192,
+ then send 219 and 220 instead. If data byte is 219, then send
+ 219 and 221 instead. When the last byte of the packet is sent
+ then send 192.
+
+
+________________________________________________________________
+ETHERNET
+
+ Ethernet Header
+
+ offset bytes meaning
+ 0 6 destination 48bit Ethernet MAC
+ 6 6 source 48bit Ethernet MAC
+ 12 2 type, ARP=0x806, IP=0x800
+ 14 total size (offset of IP header)
+
+ When get IP from network, save source MAC to IP mapping if
+ source IP is on the local network (hence the requirement of a
+ netmask). When put IP to network, set destination MAC to
+ correct MAC for destination IP (if on local network) or
+ address of default router (not on local network).
+
+ Ethernet ARP (Address Resolution Protocol) Header
+
+ offset bytes meaning
+ 14 2 hardware type: 1=ethernet
+ 16 2 protocol: IP=0x800
+ 18 1 hardware length: 6 (for 48bit Ethernet MAC)
+ 19 1 protocol length: 4 (for 32bit IP)
+ 20 2 opcode: request=1, reply=2
+ 22 6 source MAC
+ 28 4 source IP
+ 32 6 destination MAC
+ 38 4 destination IP
+
+ These packets are used to resolve IP addresses into MAC
+ addresses. After initial resolution the translation should be
+ cached. Probably should use 20 minutes as default for ARP
+ cache entry timeout (this is BSD default). If ARP request, and
+ destination IP equals host IP, then send reply with source set
+ to host info and destination set to source info from request.
+ To send an ARP request set ethernet header destination MAC to
+ all 0xFF, ARP header destination MAC to all 0x00, and set
+ source to host.
+
+
+________________________________________________________________
+DNS HOST NAME TO IP ADDRESS RESOLUTION
+
+ DNS uses UDP packets at port 53. This only gives the minimal
+ amount of into to write a simple resolver. DNS messages
+ encode host names with a special format, host dot seperated
+ substring,
+
+ offset bytes meaning
+ 0 1 n, size of string or 0 for end of string
+ 1 n the characters for the string (skips .)
+
+ This may be repeated multiple times to encode a string
+ with many '.' characters. So to encode "this.name.com",
+
+ 4,'this',4,'name',3,'com',0,
+
+ DNS Message Header
+ offset bytes meaning
+ 0 2 id (could be used for resolver table entry)
+ 2 1 flags
+ 0x80 response
+ 0x01 query
+ 3 1 flags
+ 0xf error mask
+ 0x3 error name
+ 0x0 error none
+ 4 2 number of questions, 1
+ 6 2 number of answers, 0 for query
+ 8 2 number of authority, 0
+ 10 2 number of additional, 0
+ 12 total size
+ for query
+ special formated host name follows
+ for request
+ special formated host name follows
+ then DNS answer messages follows
+
+ DNS Answer Message First Part (2 options)
+ 0 1 c0 (compressed record)
+ 1 1 skip
+
+ or a DNS encoded host name
+
+ DNS Answer Message Second Part
+ offset bytes meaning
+ 0 2 type, 1
+ 2 2 class, 1
+ 4 2 time to live
+ 6 2 length, 4
+ 8 4 IP
+ 12 total size
+
+ To query for IP address for hostname, the hostname must be
+ encoded after the message header in the special dot broken
+ encoding, followed by the following sequence of bytes:
+ 0,1,0,1. So to encode "this.name.com",
+
+ 4,'this',4,'name',3,'com',0, 0,1,0,1
+
+ When reading a DNS responce, and the second flag byte to error
+ mask to check for error. The question name is entered
+ immediately following the message header. To get to the
+ answers this name must be parsed by reading a number and then
+ skipping that number of characters, until the number read is
+ zero. You should probably check that the question matches the
+ hostname under question for security. The answers follow. The
+ answer may contain compressed name records or normal host name
+ records (with the dot broken encoding). Choose an answer with
+ a valid IP address.
+
+
+________________________________________________________________
+IP PACKETS
+
+ Offsets from Link Level Header (ethernet=14),
+
+ IP HEADER
+ offset bytes meaning
+ 0 1 vhl
+ 1 1 type of service
+ 2 2 length of packet
+ 4 2 ip id
+ 6 2 ip offset
+ 8 1 time to live, set to maximum 255 hops
+ 9 1 protocol, 1=ICMP, 6=TCP, 17=UDP
+ 10 2 ip checksum
+ 12 4 source ip address
+ 16 4 destination ip address
+ 20 total size
+
+ TCP HEADER
+ offset bytes meaning
+ 20 2 source port
+ 22 2 destination port
+ 24 4 sequence number
+ 28 4 acknowledge number
+ 32 1 tcp offset
+ 33 1 flags
+ 34 2 window
+ 36 2 tcp checksum
+ 38 2 urgp
+ 40 total size
+
+
+________________________________________________________________
+ICMP - INTERNET CONTROL MESSAGE PROTOCOL
+
+ ICMP Header
+
+ offset bytes meaning
+ 0 1 type (8=echo, 0=reply)
+ 1 1 icode (0)
+ 2 2 icmp checksum
+ 4 2 id (0 or number to help match echos and replies)
+ 6 2 sequence number (0 or like id byte)
+ 8 total size
+
+ This is only enough to do a ping. The ICMP checksum is the
+ 16bit one's complement of the one's complement of the sum of
+ the ICPM message starting at the type byte. What ever data
+ sent after the ICMP header in a echo should be returned in the
+ reply.
+
+
+________________________________________________________________
+UDP - USER DATAGRAM PROTOCOL
+
+ UDP Header
+
+ offset bytes meaning
+ 0 2 source port
+ 2 2 destination port
+ 4 2 udp length (udp header + data)
+ 6 2 udp checksum (use zero here when computing this)
+ 8 total size
+
+ The UPD packet sits on top of the IP packet. The length for a
+ zero data size packet is 8. The checksum is the 16bit one's
+ complement of the one's complement sum of a pseudo header of
+ information from the IP header, the UDP header, and the data
+ padded with zeros if necessary to make a multiple of 2 bytes.
+ The pseudo header is as follows,
+
+ offset bytes meaning
+ 0 4 source IP address
+ 4 4 destination IP address
+ 8 1 zero
+ 9 1 protocol (17 for UDP)
+ 10 2 udp length
+
+ If the computed checksum is zero it is sent as all ones. An
+ all zero checksum means that there is no checksum.
+
+
+________________________________________________________________
+FTP - FILE TRANSFER PROTOCOL
+
+ Work in progress...
+
+
+________________________________________________________________
+TCP
+
+ Work in progress...
+
+
+
+________________________________________________________________
+
+
+