Jan 26
continue discussion of binary and hex
Protocol Layers
(Lots of background / terminology here. Maybe we should start a glossary page ...)
Discuss section 2.1 of Matthews text.
- Launch Wireshark. Open simpleHttp.cap.
- How many computers? What are they?
- What are the protocols? What does "nested" mean?
- Click on the protocols in the middle pane; see which bytes are selected.
- Use middle pane to see what the numbers mean.
Note however that the text is a bit dated;
the protocols displayed are probably not what
you'll actually see. And our Wireshark doesn't
really unpack the "data" part of these packets.
Look at a capture of mine from last night; loading
a wikipedia page.
A few protocols briefly:
- 0 link) Ethernet - network (wireless or cable plugged in)
- 1 net) IP - internet protocol (from 10.1.2.3 to 10.1.2.4)
- 2 xfer) TCP - transmission control (from port 5513, to port 80, seq 143)
- 2 xfer) UDP - instead of TCP : video/audio streams
- 3 app) HTTP - HyperText Transfer Protocol (web pages)
- 3 app) SMTP - simple mail transfer protocol
- 3 app) FTP - file transfer protocol
- 3 app) DNS - domain name system (www.marlboro.edu has which IP?)
Most of these are defined by "RFC's" :
RFC : request for comments
Buzzwords and acronyms to understand :
- protocol
- protocol layering
- MAC address (ethernet address; stamped onto network card)
- IP address ( 10.1.2.23 ; assigned to computer by router)
- router (computer between you and rest of internet)
- port (address within a computer; running programs connect to ports)
- TCP (port + sequence numbers; makes packets look like 2-way flow)
- UDP (simpler than / instead of TCP; used for streams)
- HTTP (web pages)
- DNS (lookup for names like www.marlboro.edu)
Questions:
For each type of address (MAC / IP / DNS)
- What are they?
- How many can/should one computer have?
- How does a computer get one?
- How does another computer A find out what it is for computer B?
Much of this is jumping ahead; the Matthews' book
starts at the top (application layer) and looks at
the lower layers in more detail later.
chapter 2
An application protocol : HTTP
Discuss server/client paradigm.
( ... see how far we get ... assignment will be from chap 2 )
