Switches and Routers Quiz 2

ARP

Address Resolution Protocol maps IP addresses to MAC addresses - it finds the hardware address when you know the IP address.

RARP

Reverse ARP maps MAC addresses to IP addresses, allowing a device to discover its own IP address when it only knows its MAC address.

SSH

Secure Shell encrypts all communication, providing secure remote access with authentication and data protection.

Telnet

Transmits data in plain text, including passwords, making it insecure.

OSI Model Layer 7

Application: User interface and application services (HTTP, FTP, DNS).

OSI Model Layer 6

Presentation: Data formatting, encryption, compression.

OSI Model Layer 5

Session: Establishes, manages, and terminates sessions.

OSI Model Layer 4

Transport: End-to-end communication, flow control (TCP, UDP).

OSI Model Layer 3

Network: Logical addressing and routing (IP).

OSI Model Layer 2

Data Link: Physical addressing, frame formatting (MAC addresses).

OSI Model Layer 1

Physical: Raw bit transmission over physical media.

DOD Model

The DOD (TCP/IP) model has 4 layers while OSI has 7.

TCP

Transmission Control Protocol is connection-oriented, reliable, and provides sequencing, acknowledgments, flow control, and error checking.

UDP

User Datagram Protocol is connectionless, unreliable, and faster than TCP.

Well-known Ports

Ports (0-1023) reserved for standard services and require administrative privileges (HTTP-80, HTTPS-443, FTP-21, SSH-22).

Dynamically Assigned Ports

Ephemeral ports (49152-65535) temporarily assigned by the OS for client-side connections.

Registered Ports

Ports (1024-49151) that fall in between well-known and dynamically assigned ports.

DHCP

Dynamic Host Configuration Protocol automatically assigns IP addresses and network configuration to devices on a network.

DORA Process

Discover, Offer, Request, Acknowledge - the process used by DHCP.

DNS

Domain Name System translates human-readable domain names (like google.com) into IP addresses.

ICMP

Internet Control Message Protocol is a network layer protocol used for error reporting and diagnostic functions.

Ping

A tool that uses ICMP to check the reachability of a host on a network.

Traceroute

A tool that uses ICMP to trace the path packets take to a network destination.

ICMP Troubleshooting Steps

Ping localhost (127.0.0.1) to verify TCP/IP stack, Ping your own IP address to verify NIC functionality, Ping default gateway to test local network connectivity, Ping remote host to test internet/WAN connectivity, Use traceroute to identify where packets are failing, Check for ICMP blocking by firewalls if no response.

Unicast

One-to-one communication (single sender to single receiver).

Broadcast

One-to-all communication (single sender to all devices on network, uses 255.255.255.255 or subnet broadcast).

Multicast

One-to-many communication (single sender to specific group of interested receivers, uses 224.0.0.0-239.255.255.255).

Loopback Address

127.0.0.1 is the loopback address (localhost) used to test if the TCP/IP stack is properly installed on your computer. Traffic sent to this address never leaves the machine - it loops back to itself. The entire 127.0.0.0/8 range is reserved for loopback.

IPv4 Subnet Mask

In binary format, ones (1s) represent the network portion of the address, while zeros (0s) represent the host portion. For example, 255.255.255.0 in binary is 11.10, meaning the first 24 bits are the network and the last 8 bits are for hosts.

Class A Networks

First octet: 1-126 (0 and 127 reserved), Default mask: 255.0.0.0 (/8), First bit always 0, 126 networks available, 16,777,214 hosts per network, Used for very large networks.

Class B Networks

First octet: 128-191, Default mask: 255.255.0.0 (/16), First two bits always 10, 16,384 networks available, 65,534 hosts per network, Used for medium to large networks.

Class C Networks

First octet: 192-223, Default mask: 255.255.255.0 (/24), First three bits always 110, 2,097,152 networks available, 254 hosts per network, Used for small networks.

Using Ping for Troubleshooting

Follow systematic steps: ping 127.0.0.1 (loopback), ping local IP (NIC test), ping default gateway (local network), ping DNS server, ping remote IP (bypasses DNS), ping remote hostname (tests DNS). Analyze results: 100% loss = no connectivity, partial loss = congestion/intermittent issues, high latency = slow connection, TTL expired = routing loops.

Host-to-Host Layer Protocols

The main protocols are TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). This layer also includes SPX (Sequenced Packet Exchange) in IPX/SPX networks. These protocols provide end-to-end communication services and handle port numbers for multiplexing.

Subnet Calculations

Convert subnet mask to binary to find network bits, Subnet address: Set all host bits to 0, Broadcast address: Set all host bits to 1, First usable: Subnet address + 1, Last usable: Broadcast address - 1. Example: 192.168.1.65/26 → Subnet: 192.168.1.64, First: .65, Last: .126, Broadcast: .127.

VLSM Network Design

List all subnets and required host counts in descending order, Start with the largest subnet requirement, Choose the appropriate subnet mask (2^n - 2 ≥ hosts needed), Assign the subnet starting address, Calculate the next available subnet address, Repeat for remaining subnets in order. VLSM allows efficient IP address utilization by using different mask lengths for different subnets.