- Network+ Certification
- Network+ Certification – Introductions and Resources
- Network+ : From Physical Topologies to Media and Network Devices
- Network+ : Networking Variants, Physical Installation
- Network+ : TCP/IP and Network Operations
- Network+ : Network Naming and Sharing Resources
- Network+ : IPv6
- Network+ : Remote, Secure and Cross-Platform Networking
- Network+ : Servers and Support
- Network+ : WiFi
- Routing and Firewalls
- Network+: Routing Protocols
- Network+: Network Monitoring
Day 2: Chapters 3, 4 and 5
Client / Server Model
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.
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)
Layer 1 of the OSI Model: the Physical Layer
Physical media: What carries the signal (think of telegraph wire)
- Fiber optic cable
- Radio waves
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)
Media Access Control (MAC)
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:
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.
Ring: Token Ring
Mesh: Full vs Partial Mesh
Physical vs. Logical
Now we go one layer deeper.
A bus is a linear network – both physically and logically.
A star topology is physically a star (think of a hub or switch at the center of a group of hosts.
But a star topology in Ethernet physically looks like a start – but at the logical level, the way it actually functions, it uses a bus topology. Think of it this way: if you took all the wiring out of a hub and laid it out, you’d find it’s actually arranged as a bus.
This creates a “Physical Star but Logical Bus” topology. Ethernet hubs and switches use it, but so do Token Ring concentrators.
RG-8 – 10Base5
RG-58 – 10Base2
MAU or MSAU
Connectors: BNC (“bayonet”) – a steel, stick and twist connector
RG-6 – Cable TV service, analog service, security cameras
RG-62 – TV
RG-59 – Cable service : Siamese (TwinAxial) cable: coax bonded to two conductor wires (primitive “power over ethernet” – analog)
Twisted Pair Ethernet
Twisted pair Ethernet cable has 4 pairs (8 wires), but only 2 pairs are used. Theoretically this supports 2 Ethernet ports per cable, though this feature usually goes unused. Ports and jacks use the RJ-45 standard, similar to the telephone RJ-11 jack.
Get familiar with the T-568A & B jack and plug pinout configuration. Memorize the B pinouts and learn to use the acronym GO to get the A pinouts. For some reason everyone uses B most of the time. This site is clear and to-the-point:
Almost all standards for Twisted Pair call for runs of a maximum of 100 meters. In-wall cable is usually limited to 90 meters to allow patch cables at both ends.
Shielded Twisted Pair
Was mostly used with Token Ring.
Use in high-EMI/RFI areas where shielding is needed.
Unshielded Twisted Pair
10BaseT: minimum Cat 3
100BaseTX, which became simply
100BaseT: minimum Cat 5
100BaseT4: an early alternative that used all 4 pairs in a Cat 3 cable
1000BaseT or 1GBaseT: Cat5e
10GBaseT: Cat 6 will get you 55 meters, Cat 6a will get you 100 meters.
LEDs – short distance
Lasers – long distance
Multimode fiber: usually orange; short distance; uses multiplexing, for instance three different signals: red, green and blue
Single-mode fiber: usually yellow; long distance; simplex: only one signal stream
Physical Contact (PC) Connectors
Ultra Physical Contact (UPC)
Angled Physical Contact (APC)
10BaseFL – early fiber optic
1000BaseSX: “S for short” distance, up to 500 meters
1000BaseLX: “L for long” distance, up to 5 kilometers
ATM over SONET rings
The national long-distance telephone system.
ATM used 53 byte cells
Metro Ethernet over SONET
Uses SONET rings, so 10GB
10GBaseSR: S for short; R is for eth-R-net; multimode; 300 meters
10GBaseSW: W is for WAN (meaning ATM signaling, not Ethernet); multimode; 300 meters
10GBaseLR: Ethernet, single-mode; 10 kilometers
10GBaseLW: WAN/ATM; 10 km
10GBaseER: E is for extra-long; ethernet; 40 km
10GBaseEW: WAN/ATM; 40 km
ST – Stick and Twist
SC – Stick and Click
LC – the “Little Connector” (actually Lucent)
Early Gigabit Media
1000BaseCX (copper, 25 yd)
1000BaseSX (“short” fiber-optic)
1000BaseLX (“long” fiber-optic)
Repeater – Layer 1 – usually for coaxial, but there are twisted pair repeaters too.
Bridge – Layer 2 – also usually for coax, and essentially a 2-port switch, i.e. it keeps a MAC table.
Hub – Layer 1 – has no MAC filtering.
Switch – Layer 2 – isolates traffic based on MAC addresses.
Router – Layer 3 – routes internet traffic based on IP addresses. This is the only Layer 3 box in this list.