Free CCNA | Interfaces and Cables | Day 2 | CCNA 200-301 Complete Course

Interfaces and Cables

This CCNA lesson explains how network devices connect over copper and fiber-optic cables, how Ethernet cabling standards work, and when different cable types are appropriate.

Interfaces, Ethernet, and Data Rates

• Switches commonly provide multiple RJ-45 ports for connecting end devices. RJ-45 connectors are used with copper Ethernet cables.
• Ethernet is a family of network protocols and standards. Industry standards allow devices and cables from different manufacturers to connect and communicate.
• Network speeds are measured in bits per second. A byte is 8 bits, so a gigabyte is eight times the size of a gigabit.
• Common copper Ethernet standards include:
  • 10BASE-T: 10 Mb/s
  • 100BASE-T: 100 Mb/s
  • 1000BASE-T: 1 Gb/s
  • 10GBASE-T: 10 Gb/s
• These standards are part of IEEE 802.3. The “T” indicates twisted-pair cabling. The lesson gives 100 meters as the maximum distance for these UTP connections.

Copper UTP Cables and Pin Use

UTP means Unshielded Twisted Pair. A cable contains four twisted pairs, for a total of eight wires. Twisting helps reduce electromagnetic interference, although unshielded cable can still be susceptible to it.

10BASE-T and 100BASE-T use two pairs:

• Pins 1–2
• Pins 3–6

PCs, routers, and firewalls transmit on pins 1–2 and receive on pins 3–6. Switches use the opposite arrangement: they receive on pins 1–2 and transmit on pins 3–6.

• Straight-through cables connect corresponding pins at both ends. They are conventionally used between unlike device types, such as a PC and a switch.
• Crossover cables swap the 1–2 and 3–6 pairs. Traditionally, they were needed to connect like device types, such as two switches or two routers, or to connect a PC directly to a router.
• Many modern devices support Auto MDI-X, which detects the other device’s transmit and receive wiring and adjusts automatically. This generally removes the need to choose between straight-through and crossover cables manually.

1000BASE-T and 10GBASE-T use all four wire pairs. In these standards, each pair is bidirectional rather than being assigned only to transmit or receive.

Fiber-Optic Cabling

Fiber uses light transmitted through glass fibers rather than electrical signals over copper. Devices typically use SFP transceivers to connect fiber cables. A duplex fiber connection has separate paths for transmitting and receiving.

A fiber-optic cable includes a glass core, reflective cladding, a protective buffer, and an outer jacket.

Multimode Fiber

• Multimode fiber (MMF) has a wider core and allows multiple light paths, or modes.
• It supports longer distances than UTP, but shorter distances than single-mode fiber.
• It is generally less expensive than single-mode fiber because it can use cheaper, often LED-based transmitters.

Single-Mode Fiber

• Single-mode fiber (SMF) has a narrower core and carries light along a single mode, using a laser-based transmitter.
• It supports the longest distances, but is generally more expensive.

The lesson reviews these example fiber standards and maximum distances:

Standard Fiber type Maximum distance 1000BASE-LX Multimode 550 m 1000BASE-LX Single-mode 5 km 10GBASE-SR Multimode 400 m 10GBASE-LR Single-mode 10 km 10GBASE-ER Single-mode 30 km

Cable Trade-Offs

• UTP is less expensive and widely used to connect end hosts to switches. It is limited to about 100 m, may be vulnerable to electromagnetic interference, and may leak a faint signal outside the cable.
• Fiber is more expensive, including its transceivers, but supports longer distances. It is not affected by electromagnetic interference and does not emit a signal outside the cable in the way described for UTP.
• Single-mode fiber and its ports are typically more expensive than multimode fiber and its ports.

Quiz and Study Materials

The video includes a five-question review quiz. Its key conclusions are:

1. Two older routers connected with a straight-through cable may fail to communicate. If Auto MDI-X is unavailable, a crossover cable is the traditional fix.
2. For a 150-meter building-to-building link where cost matters, multimode fiber is suitable.
3. For a 3-kilometer link, single-mode fiber is required among the options given.
4. Auto MDI-X-enabled switches can communicate normally over a straight-through cable.
5. UTP is the standard choice for connecting many nearby office end hosts to a switch.

The presenter recommends downloadable Anki flashcards for review and mentions a Packet Tracer practice lab released separately.

Main speaker/source: Jeremy of Jeremy’s IT Lab. The lesson references IEEE 802.3 Ethernet standards.