cable,route,interview

Cat5

Cat5 is an older Ethernet copper cable. In practice, it was mainly used for 100 Mbps networks, with a maximum distance of around 100 meters.

Cat5e

Cat5e is still very common in office networks. It can support 1 Gbps Ethernet up to 100 meters, so it is usually enough for normal PCs and printers.

Cat6

Cat6 is a better copper cable than Cat5e. It supports 1 Gbps up to 100 meters and can support 10 Gbps only at shorter distances, usually around 55 meters or less.

Cat6A

Cat6A is a good choice for new office cabling. It supports 10 Gbps Ethernet up to 100 meters and is more future-proof than Cat5e or Cat6.

Cat7

Cat7 is a shielded copper cable that can support high speed such as 10 Gbps, but it is not as commonly used in normal enterprise LAN deployments as Cat6A.

Cat8

Cat8 is a very high-speed copper cable, mainly used in data centers. It can support 25G or 40G, but only over short distances, usually up to about 30 meters.

UTP

UTP means Unshielded Twisted Pair. It is the most common Ethernet cable type in offices because it is cheaper, flexible, and easy to install.

STP cable

STP means Shielded Twisted Pair. It has extra shielding to reduce interference, but it needs proper grounding to work well.

RJ45

RJ45 is the common connector used for Ethernet copper cables like Cat5e, Cat6, and Cat6A.

T568A and T568B

T568A and T568B are two wiring standards for terminating RJ45 cables. In practice, T568B is very common, but either one works if both ends are consistent.

Straight-through cable

A straight-through cable uses the same wiring standard on both ends, such as T568B to T568B. It is commonly used to connect a PC to a switch.

Crossover cable

A crossover cable swaps the transmit and receive pairs. It was used for connecting similar devices, like switch to switch, but modern ports usually support Auto MDI-X.

Auto MDI-X

Auto MDI-X allows modern Ethernet ports to automatically detect cable type, so straight-through cables usually work even between similar devices.

100BASE-TX

100BASE-TX is Fast Ethernet over copper. It supports 100 Mbps up to 100 meters and uses two pairs of wires.

1000BASE-T

1000BASE-T is Gigabit Ethernet over copper. It supports 1 Gbps up to 100 meters and uses all four pairs of wires.

10GBASE-T

10GBASE-T is 10 Gigabit Ethernet over copper. For reliable 10G over 100 meters, Cat6A is normally preferred.

Copper Ethernet distance

The typical maximum distance for copper Ethernet is 100 meters. In real installations, this includes the cable in the wall plus patch cords.

Permanent link

A permanent link is the fixed cable path, usually from patch panel to wall outlet. It is usually designed to stay within about 90 meters.

Channel link

A channel link includes the permanent cable plus patch cords at both ends. The common maximum length is around 100 meters.

PoE

PoE means Power over Ethernet. It allows one Ethernet cable to carry both data and power for devices like IP phones, cameras, and wireless access points.

PoE 802.3af

802.3af is the basic PoE standard. It can provide up to 15.4 watts from the switch side.

PoE+ 802.3at

802.3at is also called PoE+. It can provide up to 30 watts from the switch side and is common for access points and cameras.

PoE++ 802.3bt

802.3bt is also called PoE++ or 4PPoE. It provides higher power and is used for devices like Wi-Fi 6 APs, PTZ cameras, or thin clients.

Fiber-optic cable

Fiber-optic cable uses light to transmit data. It is better than copper for long distance, high speed, and areas with electrical interference.

Multimode fiber

Multimode fiber is usually used for short-distance links, such as inside a building, between floors, or inside a data center.

Single-mode fiber

Single-mode fiber is used for longer distances, such as between buildings, campus networks, ISP links, and long-distance uplinks.

OM3

OM3 is a common multimode fiber type. It is often used for 10G short-reach links, especially inside buildings or data centers.

OM4

OM4 is an improved multimode fiber type. It supports longer high-speed links than OM3 and is common in modern data centers.

OS2

OS2 is a common single-mode fiber type. It is used for long-distance fiber links and can support several kilometers depending on the transceiver.

LC connector

LC is a small fiber connector commonly used with SFP, SFP+, SFP28, and many modern switch modules.

SC connector

SC is a larger fiber connector. It is often seen in older fiber patch panels or ISP handoff points.

SFP

SFP is a small transceiver module commonly used for 1 Gbps fiber or copper links.

SFP+

SFP+ is similar to SFP but supports higher speed, commonly 10 Gbps.

SFP28

SFP28 is commonly used for 25 Gbps links, especially in server and data center networks.

QSFP+

QSFP+ is commonly used for 40 Gbps links.

QSFP28

QSFP28 is commonly used for 100 Gbps links.

SR transceiver

SR means Short Reach. It is usually used with multimode fiber for short-distance links, such as inside a data center.

LR transceiver

LR means Long Reach. It is usually used with single-mode fiber for longer-distance links, often up to several kilometers depending on the module.

ER transceiver

ER means Extended Reach. It is used for longer fiber distances than LR, depending on the transceiver and fiber quality.

DAC cable

DAC means Direct Attach Copper. It is used for short, high-speed connections, usually inside the same rack or between nearby racks.

AOC cable

AOC means Active Optical Cable. It is used for high-speed links like DAC, but it uses optical technology and can support longer distances than DAC.

Fiber link troubleshooting

If a fiber link does not come up, I would check the transceiver type, fiber type, connector cleanliness, TX/RX polarity, distance, and switch compatibility.

Wi-Fi 4

Wi-Fi 4 is based on 802.11n. It supports 2.4 GHz and 5 GHz, but in practice it is older and slower than Wi-Fi 5 or Wi-Fi 6.

Wi-Fi 5

Wi-Fi 5 is based on 802.11ac. It mainly works on 5 GHz and is faster than Wi-Fi 4, but it is not as efficient as Wi-Fi 6 in dense environments.

Wi-Fi 6

Wi-Fi 6 is based on 802.11ax. It improves speed, latency, and capacity, especially when many users connect to the same wireless network.

Wi-Fi 6E

Wi-Fi 6E is basically Wi-Fi 6 extended to the 6 GHz band. It provides more clean channels, but both the AP and client must support 6 GHz.

Wi-Fi 7

Wi-Fi 7 is based on 802.11be. It is designed for higher throughput, lower latency, wider channels, and better performance with modern devices.

2.4 GHz Wi-Fi

2.4 GHz Wi-Fi has better range and wall penetration, but it is slower and more crowded because many devices use this band.

5 GHz Wi-Fi

5 GHz Wi-Fi is faster and usually less crowded than 2.4 GHz, but it has shorter range and weaker wall penetration.

6 GHz Wi-Fi

6 GHz Wi-Fi has more available channels and less interference, but the range is shorter and it requires Wi-Fi 6E or Wi-Fi 7 devices.

OFDMA

OFDMA is a Wi-Fi 6 feature that allows an access point to serve multiple clients more efficiently by splitting the channel into smaller resource units.

MU-MIMO

MU-MIMO allows an access point to communicate with multiple clients at the same time, improving performance in multi-user environments.

Target Wake Time

Target Wake Time is a Wi-Fi 6 feature that helps client devices save battery by scheduling when they wake up to send or receive data.

SSID

SSID is the Wi-Fi network name that users see when they connect to wireless.

BSSID

BSSID is the MAC address of a specific access point radio. One SSID can have multiple BSSIDs if many APs broadcast the same Wi-Fi name.

Wired backhaul

Wired backhaul means the access point connects back to the network using Ethernet. It is usually more stable and faster than wireless mesh backhaul.

Wireless mesh backhaul

Wireless mesh backhaul means APs connect to each other wirelessly. It is easier to install but usually has lower performance than wired backhaul.

802.1Q

802.1Q is the VLAN tagging standard. It allows multiple VLANs to travel across one trunk link by adding a VLAN tag to Ethernet frames.

VLAN

A VLAN is a logical Layer 2 network. It separates devices into different broadcast domains, such as Users, Guests, Cameras, and Servers.

Access port

An access port carries traffic for one VLAN only. It is usually used for end devices like PCs, printers, cameras, and IP phones.

Trunk port

A trunk port carries multiple VLANs over one physical link. It is commonly used between switches, or between a switch and a router, firewall, or access point.

Native VLAN

The native VLAN is the VLAN used for untagged traffic on an 802.1Q trunk. In practice, it should be configured carefully for security.

Allowed VLAN list

An allowed VLAN list controls which VLANs can pass through a trunk. It helps reduce unnecessary traffic and improves security.

Inter-VLAN routing

Inter-VLAN routing allows devices in different VLANs to communicate. It requires a Layer 3 device like a router, Layer 3 switch, or firewall.

Router-on-a-stick

Router-on-a-stick uses one physical router interface with multiple subinterfaces. Each subinterface handles one VLAN using 802.1Q tagging.

Subinterface

A subinterface is a logical interface under a router physical interface. It is often used in router-on-a-stick for different VLAN gateways.

SVI

An SVI is a virtual Layer 3 interface for a VLAN on a Layer 3 switch. It is commonly used as the default gateway for that VLAN.

Routed port

A routed port is a physical Layer 3 port on a Layer 3 switch. It has an IP address and works like a router interface.

Default gateway

A default gateway is the IP address a host uses to reach other networks. For example, a PC in VLAN 10 may use 192.168.10.1 as its gateway.

Directly connected network

A directly connected network is a network that is directly attached to one of the router or Layer 3 switch interfaces.

Static route

A static route is a manually configured route. It tells the router where to send traffic for a specific remote network.

Dynamic routing

Dynamic routing uses protocols like OSPF or EIGRP to automatically learn and update routes between routers.

OSPF

OSPF is a dynamic routing protocol used to find the best path between IP networks. It is common in enterprise networks.

EIGRP

EIGRP is a dynamic routing protocol developed by Cisco. It can quickly learn routes and find efficient paths.

STP

STP prevents Layer 2 loops in a switched network. It blocks redundant paths but can unblock them if the main link fails.

EtherChannel

EtherChannel combines multiple physical switch links into one logical link. It improves redundancy and can increase total bandwidth.

Port-channel

A port-channel is the logical interface created by EtherChannel. In practice, we configure trunk or access settings on the port-channel interface.

LACP

LACP is a standard protocol used to negotiate and manage EtherChannel links between devices.

Broadcast domain

A broadcast domain is an area where broadcast traffic can reach all devices. Each VLAN is usually one broadcast domain.

Collision domain

A collision domain is an area where Ethernet collisions can happen. It is mostly a legacy concept because modern switched Ethernet is full-duplex.

Why can a Cat6 cable link only show 100 Mbps?

Even if the cable says Cat6, the link may drop to 100 Mbps if the cable is damaged, terminated incorrectly, has bad pairs, or connects to a 100 Mbps port.

Why can a 1 Gbps network feel slow?

A 1 Gbps link only shows the physical link speed. Real performance can be lower because of disk speed, server load, congestion, bad cables, or application limits.

Why does Wi-Fi not reach the advertised speed?

Wi-Fi speeds are theoretical maximums. Real speed depends on distance, walls, interference, channel width, number of users, and client device capability.

Why is Cat6A better than Cat6 for 10G?

Cat6A is designed to support 10G up to 100 meters, while Cat6 can usually support 10G only at shorter distances.

Why use fiber between floors or buildings?

Fiber is better for uplinks because it supports longer distance, higher speed, and is not affected by electrical interference like copper.

Why should copper Ethernet stay under 100 meters?

After about 100 meters, signal quality becomes worse, which can cause errors, packet loss, or lower negotiated speed.

Why do we need VLANs?

We use VLANs to separate different types of devices, reduce broadcast scope, improve security, and make the network easier to manage.

Why do devices in different VLANs need routing?

Different VLANs are separate Layer 2 networks. To communicate between them, traffic must go through a Layer 3 device.

Why does a trunk need VLAN tagging?

A trunk carries multiple VLANs on one link, so VLAN tags are needed to identify which frame belongs to which VLAN.

Why use an allowed VLAN list on a trunk?

An allowed VLAN list prevents unnecessary VLANs from passing through the trunk and reduces security risk.

Why use SVI on a Layer 3 switch?

An SVI is used as the default gateway for a VLAN and allows the Layer 3 switch to route between VLANs.

Why use a firewall between LAN and Internet?

A firewall controls traffic between trusted and untrusted networks, performs NAT, applies security policies, and protects internal systems.

Why is wired backhaul better for APs?

Wired backhaul gives each AP a stable Ethernet connection. It usually provides better speed and reliability than wireless mesh backhaul.

Why should AP transmit power not always be set to maximum?

Maximum transmit power can create interference and poor roaming. Clients may stay connected to a far AP instead of moving to a closer one.

Why is channel planning important for Wi-Fi?

Channel planning reduces interference between APs and improves wireless stability and performance.

Why is cable labeling important?

Cable labeling helps engineers quickly identify where each cable goes, which switch port it connects to, and how to troubleshoot issues.

Why should cable testing be done after installation?

Cable testing checks wire map, length, signal quality, and termination errors before the network goes into production.

Why can a fiber link fail even if the cable is correct?

A fiber link can fail because of dirty connectors, wrong transceiver type, wrong fiber type, TX/RX reversed, unsupported modules, or distance mismatch.

Theory vs real deployment

In theory, standards show maximum speed and distance. In real deployment, performance depends on cable quality, installation, connectors, device support, interference, and testing.

Cat5e vs Cat6A

Cat5e is usually enough for 1G up to 100 meters. Cat6A is better for new cabling because it supports 10G up to 100 meters.