Internet Message Formats

Here are related Message Format Structure  information:
We will use a HTTP request message captured using Ethereal package to give examples of the fields and their values.
It is the frame 11 in http://cs.uccs.edu/~cs522/ethereal/ethdetail.txt.

Ethereal provides pretty good explanation of each fields in the protocol message.  It is available at http://www.ethereal.com/.

This is a HTTP request message generated  by typing "cs.uccs.edu/~cs522/" on a browser on wait.uccs.edu.
Wait  is a Dell machine with one of its NIC (network inteface card) configured with the IP address of 128.198.192.202 and it is on subnet 128.198.192/21.
The NIC card's burn in Ethernet address or MAC address is 00:a0:24:56:9c:33. (hexadecimal representation).
The browser application has a socket connection with port number=1089.
Note that this ethernet frame will be received by the router, 00:50:80:d1:36:00 (cs-old-loadbalancing-router.uccs.edu) with IP address 128.198.192.1 , which will look up its routing table to route the IP packet to the cs.uccs.edu machine.

        Ethernet Frame Format:

Example:
Ethernet II
    Destination: 00:50:80:d1:36:00 (cs-old-loadbalancing-router.uccs.edu)
    Source: 00:a0:24:56:9c:33 (wait.uccs.edu)
    Type: IP (0x0800)
 

IP Header Format, Page 548:



Version: 4=IPv4, 5=ST2, 6=IPv6

IHL: Internet Header Length, if no option, IHL=5 words (32bits/word)

Options: used to indicate security, source routing, timestamp at each router

Total length: bytes including header and data

TTL: TimeToLive, # of hops allowed to traverse the net.

TOS: type of Service: indicate priority, delay, thruput, reliability, cost.

Protocol: 1=ICMP, 6=TCP, 17=UDP

Example:
Internet Protocol
   Version: 4
    Header length: 20 bytes
    Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
        0000 00.. = Differentiated Services Codepoint: Default (0x00)
        .... ..0. = ECN-Capable Transport (ECT): 0
        .... ...0 = ECN-CE: 0
    Total Length: 338
    Identification: 0x022a
    Flags: 0x04
        .1.. = Don't fragment: Set
        ..0. = More fragments: Not set
    Fragment offset: 0
    Time to live: 64
    Protocol: TCP (0x06)
    Header checksum: 0xd2e0 (correct)
    Source: wait.uccs.edu (128.198.192.202)
    Destination: cs.uccs.edu (128.198.162.68)
 

TCP Header, Page 575:


 

Example:

Transmission Control Protocol, Src Port: 1089 (1089), Dst Port: www (80), Seq: 4211769965, Ack: 4202585077
    Source port: 1089 (1089)
    Destination port: www (80)
    Sequence number: 4211769965
    Next sequence number: 4211770251
    Acknowledgement number: 4202585077
    Header length: 32 bytes
    Flags: 0x0018 (PSH, ACK)
        0... .... = Congestion Window Reduced (CWR): Not set
        .0.. .... = ECN-Echo: Not set
        ..0. .... = Urgent: Not set
        ...1 .... = Acknowledgment: Set
        .... 1... = Push: Set
        .... .0.. = Reset: Not set
        .... ..0. = Syn: Not set
        .... ...0 = Fin: Not set
    Window size: 32120
    Checksum: 0xee84 (correct)
    Options: (12 bytes)
        NOP
        NOP
        Time stamp: tsval 131162, tsecr 25793513
 

UDP Header, Page 569:



HTTP Messages:

Example:
Hypertext Transfer Protocol
    GET /~cs522/ HTTP/1.0\r\n
    Connection: Keep-Alive\r\n
    User-Agent: Mozilla/4.77 [en] (X11; U; Linux 2.2.16-3 i686)\r\n
    Host: cs.uccs.edu\r\n
    Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, image/png, */*\r\n
    Accept-Encoding: gzip\r\n
    Accept-Language: en\r\n
    Accept-Charset: iso-8859-1,*,utf-8\r\n
    \r\n