Unit 3
Chapter 1
Network Commands
arp # (Linux and Windows) ping # (Linux and Windows) ipconfig # (Windows) ifconfig # (old Linux command; deprecated) ip # (new Linux command) iwconfig # (Linux wifi) nslookup # (Linux and Windows) dig # (Linux native, Windows installable) traceroute # (Linux) tracert # (Windows) net # (Windows) netstat # (Windows and Linux) nbtstat # (Windows) netsh # (Windows)
Wi
Client / Server Model
Hosts
Clients: Either a physical machine like your PC or workstation, or more accurately, a “receiving end” application like your web browser. The client will connect to the server’s IP address and the service’s port number, eg.
175.63.20.6:80
Servers: either physical machines or service daemons, like web servers, mail servers, streaming servers, etc.). The server will accept connections from clients at the server’s IP address and port number.
There’s more to this, so don’t forget this model.
Local Area Networks (LANs)
The TCP/IP Model and the OSI Model
Layer 1 of the OSI Model: the Physical Layer
Physical media: What carries the signal (think of telegraph wire)
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- Wire
- Fiber optic cable
- Radio waves
- Infrared
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Layer 2: The Data Link Layer
Layer 2 of the OSI is … a mistake. ISO ignores the fact that there are two protocols at work there: a Logical Link Control layer that sets up sessions and handles multiplexing, and a Media Access Control layer that handles addressing using MAC addresses.
Logical Link Control (LLC)
https://en.wikipedia.org/wiki/Logical_link_control
Media Access Control (MAC)
https://en.wikipedia.org/wiki/Data_link_layer
MAC Addresses
NICs have “permanent” hardware addresses (Physical Addresses in Windows): MAC Addresses.
Mac Addresses are written in hexadecimal:
Base 16 notation, using 0-9 and A-F to express numbers from 0-15:
0 1 2 3 4 5 6 7 8 9 a b c d e f
Grouped in six pairs of hex numbers with a separator in between:
Generic hex numbers in the wild look like this:
0f38 – just the number
0x0f38 – “0x” means “hex”
0f38h – “h” means “hex”
So actual MAC addresses look like this:
92-fb-ad-07-64-3a
92:fb:ad:07:64:3a
92:FB:AD:07:64:3A
And the delimiter can be a colon ( : ), a dash ( – ), or anything else. The delimiters aren’t really there; they are put in for our feeble human minds.
Signal Protocols: How the message gets passed (think of Morse Code)
Ethernet, Token Ring, DECnet, X.25, IPXSPX, Banyan Vines, etc.
Today, mostly Ethernet
Ethernet passes frames. (You could call them packets, but the other kids on the playground will make fun of you.)
Ethernet cards are NICs (network interface cards, also called “host adapters”).
Full vs. Half-duplex
It wasn’t until we got switches that we could use full duplex communication. In other words, both hosts can talk non-stop, and listen non-stop, full-time, with no collisions!
This was a huge step. Every session between hosts is on its own private collision domain: there ARE no collisions. Ethernet became hugely faster with this innovation.
LAN Models and Network Operating Systems
The oldest network model:
Application
Communication
Physical
Network Operating Systems
Models
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- Client/Server
- Peer-to-Peer
- Resource-Based (Workgroup)
- Server-Based (Domain)
- Organization-Based (Directory)
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https://en.wikipedia.org/wiki/LAN_Manager
NetBEUI/NetBIOS – IBM and MS
LAN only, using MAC addresses for addressing and NetBios for naming.
NetBIOS name: 15 chars. max
NetBIOS NW Model:
Application
NetBIOS (naming)
NetBEUI (addressing)
Physical
Novell/Netware
IPX/SPX
LAN only
WINS
A cheat to resolve NetBIOS names across IP subnets. Normally NetBIOS stuff is confined to the local network.