# CCNA Quick Reference Notes

- Computer Network: Digital Telecommunications network that allows nodes to share resources
- Switches: Layer 2 devices that with many ports that connect hosts on a LAN.
- Router: Layer 3 devices that have fewer ports and connects LANs together.
- Ethernet: A collection of network protocols and standards
- Ethernet standards: IEEE 802.3 (1983)
    - 10Mbps Ethernet: 802.3i 10BASE-T 100m
    - 100Mbps Fast Ethernet: 802.3u 100BASE-T 100m
    - 1000Mbps Gig. Ethernet: 802.3ab 1000BASE-T 100m
    - 10Gbps 10 Gig. Ethernet: 802.3an 10GBASE-T 100m
- PCs - Transport (TX) data on pins one and two.
- Switches - Recieve (RX) data on pins one and two.
- PCs - RX on pins three and six.
- Switches - TX on three and six.
- Fiber Optic Connections: IEEE 802.3.ae
- Single mode:
    - Narrower than multimode
    - Light enters at a single angle from a laser based transmitter.
    - Allows longer cables then UTP and multimode fiber.
    - More expensive then multimode.
- Multimode fiber:
    - Wider than single mode.
    - Allows multiple light waves to enter the core.
    - Allows longer cables than UTP but shorter than single mode.
    - Cheaper than single mode being LED-based.
- Fiber Optic Standards:
    - 1000BASE-LX 802.3Z 1Gbps multi/single 5km single
    - 10GBASE-SR 802.3ae 10Gbps multi 400km
    - 10GBASE-LR 802.3ae 10Gbps single 10kilo
    - 10GBASE-ER 802.3ae 10Gbps single 30kilo

## OSI Model

Application
Presentation
Session
Transport
Network
Data Link
Physical

MAC Address: 6 bytes (48-bits)

## VLANs

- A LAN is a single broadcast domain.
- A broadcast domain is a group of devices which will receieve a broadcast frame. (Destination MAC: FFFFF:FFFFF:FFFFF)
- Lots of unnecessary broadcasts traffice can reduce network performance

### What is a VLAN?

- Logically seperates end-hosts at Layer 2.
- Are configured on Layer 2 switches on a per-interface bases.
- Any end host connected to that interface is part of the VLAN.

### Configuring a VLAN

- `# sh vlan br`
- `# switchport mode access`

An access port is a port is a port that belongs to a single VLAN, untagged port.

Switchports that carry multiple VLANs are called trunk ports, tagged ports.