CompTIA A+ Networking Summary

HTTPS is web traffic protected by encryption, and it uses port 443 by default. Plain HTTP uses port 80. Remember the pair: 80 for HTTP, 443 for HTTPS.

Wrong choices

• 80: Port 80 is used by HTTP, the unencrypted version of web traffic.
• 3389: Port 3389 is used by Remote Desktop Protocol (RDP).
• 22: Port 22 is used by SSH for secure remote command-line access.

SSH (Secure Shell) uses port 22 and encrypts the whole session, including the login. It is the standard way to manage Linux servers and network devices from the command line.

Wrong choices

• Telnet: Telnet also gives remote command-line access, but it sends everything, including passwords, in plain text.
• FTP: FTP transfers files. It is not used for a remote command line, and basic FTP is not encrypted.
• RDP: RDP gives a graphical remote desktop, mainly for Windows, not a command-line session to a Linux server.

When a Windows PC is set to get an address automatically but no DHCP server answers, it assigns itself an APIPA address in the 169.254.x.x range. With this address it can only talk to nearby devices on the same network, so it cannot reach the internet. Check the cable or Wi-Fi link and the DHCP server.

Wrong choices

• The DNS server is not answering: A DNS problem stops names from resolving, but it does not cause the PC to give itself a 169.254 address.
• The PC has a correctly set static IP address: A 169.254 address is assigned automatically when DHCP fails. It is not a normal static address.
• The PC has a public internet address from the ISP: 169.254.x.x is a link-local (APIPA) range. It is never a public internet address.

DNS (Domain Name System) works like a phone book for networks. It turns names that people remember into the IP addresses computers use. DNS uses port 53.

Wrong choices

• SMTP: SMTP sends email. It does not translate names into addresses.
• DHCP: DHCP hands out IP addresses to devices. It does not look up names.
• LDAP: LDAP is used to look up users and objects in a directory, not to turn web names into IP addresses.

Here is how to narrow it down:

1. The ping by IP address works, so the cable, IP address, and gateway are fine.
2. Only the name fails, and turning a name into an address is the job of DNS.
3. So the next thing to check is which DNS server the PC uses and whether it answers.

Wrong choices

• The network cable on the user's PC: The ping by IP proves the cable and network link are working.
• The DHCP lease on the user's PC: The PC already has a working address, since the ping by IP succeeds. DHCP is not the issue.
• The default gateway setting: The ping by IP address reached the server, so traffic is already leaving the local network. The gateway is working.

A router connects different networks and decides where to send traffic based on IP addresses. In a home or small office, it sits between the local network and the internet provider's network.

Wrong choices

• Wireless access point: An access point adds Wi-Fi to an existing network. It does not route between networks.
• Switch: A switch connects devices within the same network. It does not route traffic between different networks.
• Patch panel: A patch panel is a passive connection point for cables. It does not forward traffic on its own.

A toner probe has two parts. The tone generator connects to the cable at the wall jack and sends a signal down it. The technician then moves the probe across the patch panel until it picks up the tone, which shows the matching cable.

Wrong choices

• Crimper: A crimper attaches RJ45 plugs to the ends of network cables. It does not trace cables.
• Punchdown tool: A punchdown tool presses wires into a patch panel or keystone jack. It does not find which cable is which.
• Loopback plug: A loopback plug tests whether a network port can send and receive. It does not trace a cable through a wall.

SMTP (Simple Mail Transfer Protocol), port 25, sends email from a client to a server and between mail servers. To receive mail, clients use POP3 (port 110) or IMAP (port 143).

Wrong choices

• SNMP: SNMP is used to monitor network devices. It has nothing to do with sending email.
• POP3: POP3 is used to download email from the server to the device, not to send mail.
• IMAP: IMAP is used to read and manage email that stays on the server, not to send mail.

Channels in the 2.4 GHz band are close together and each one is wide enough to spill into its neighbors. Channels 1, 6, and 11 are far enough apart that they do not overlap, so nearby access points on those channels interfere with each other less.

Wrong choices

• 6, 7, and 8: These channels are side by side and overlap almost completely.
• 1, 2, and 3: These channels sit right next to each other and overlap heavily in the 2.4 GHz band.
• 2, 4, and 6: These channels are only two apart, so they still overlap with each other.

Non-secure websites use HTTP on port 80, and secure websites use HTTPS on port 443. Allowing both ports lets users open either kind of site.

Wrong choices

• 53 and 3389: Port 53 is DNS, which browsing needs but is not web traffic itself, and 3389 is Remote Desktop.
• 21 and 22: Ports 21 and 22 are used by FTP and SSH, not web browsing.
• 25 and 110: Ports 25 and 110 are used by SMTP and POP3 for email, not web browsing.