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Networking 101 v2

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Rupert Pattisson
Rupert Pattisson

This document provides an overview of networking terminology and troubleshooting techniques. It defines common networking terms like DNS, DHCP, and IP configurations. It also explains the bottom three layers of the OSI model: layer 1 deals with physical connections, layer 2 with data linking within a local network using MAC addresses, and layer 3 handles routing packets between local networks using IP addresses. Finally, it provides a troubleshooting checklist to methodically diagnose network issues starting with basic connectivity tests and escalating to external routing.

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Networking 101:1 Onsites Bench Team Meeting
Terminology/Toolkit Infrastructure DNS DHCP Gatekeeper Statically configured devices Command line getmac /v ipconfig on Windows, ifconfig on OSX/Linux tracert eg tracert yahoo.com nslookup Ping Arp -a
More terminology IPv4 addresses Valid IP/Lease Internal -10.10.x.x used for FIT phones, 172.16.x.x used for FIT network infrastructure These cannot be externally routed over the internet External or Public 163.118.x.x Invalid 169.254.x.x, or 192.168.x.x in a dorm, unless behind a student router The subnet mask Defines the specific network If entered wrongly, on a statically configured device, it will not communicate! The gateway This is actually the router Set by/implied by the subnet mask If entered wrongly, on a statically configured device, it will not communicate!
Some technical background.. Know the bottom three layers of the OSI model 7 - Application 6 - Presentation 5 - Session 4 - Transport 3 - Network do you have a valid IP can you ping externally? can you tracert to an external host 2 - Datalink can you ping the gateway? Arp-a 1 - Physical does it have a link?
Layer 1 - Physical Signal consists of high and low voltage, which is transformed into a bitstream Equipment Cables, Jacks, Connectors, NICs Can be intercepted - reason why encryption is needed!
Layer 2 Data-Link Converts bits to frames Connects hosts in the LOCAL network No frames leave the local network Bridges between layers 1 and 3 No IPs, only MACs used between hosts ARP table MAC addresses globally unique * Broadcasts/Collisions Equipment Switches
Layer 3 Network Converts Frame into a Packet by encapsulation Responsible for routing from source to destination Used to connect LOCAL networks together
Another diagram of routing
Troubleshooting Order network checklist Start by checking device registration Do you have a link? Can you ping the loopback 127.0.0.1 address? Can you ping the default gateway Do you have a valid IP? Can you tracert to an external IP address eg 8.8.8.8 (google) or yahoo.com?

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Networking 101 v2

  • 2. Terminology/Toolkit Infrastructure DNS DHCP Gatekeeper Statically configured devices Command line getmac /v ipconfig on Windows, ifconfig on OSX/Linux tracert eg tracert yahoo.com nslookup Ping Arp -a
  • 3. More terminology IPv4 addresses Valid IP/Lease Internal -10.10.x.x used for FIT phones, 172.16.x.x used for FIT network infrastructure These cannot be externally routed over the internet External or Public 163.118.x.x Invalid 169.254.x.x, or 192.168.x.x in a dorm, unless behind a student router The subnet mask Defines the specific network If entered wrongly, on a statically configured device, it will not communicate! The gateway This is actually the router Set by/implied by the subnet mask If entered wrongly, on a statically configured device, it will not communicate!
  • 4. Some technical background.. Know the bottom three layers of the OSI model 7 - Application 6 - Presentation 5 - Session 4 - Transport 3 - Network do you have a valid IP can you ping externally? can you tracert to an external host 2 - Datalink can you ping the gateway? Arp-a 1 - Physical does it have a link?
  • 5. Layer 1 - Physical Signal consists of high and low voltage, which is transformed into a bitstream Equipment Cables, Jacks, Connectors, NICs Can be intercepted - reason why encryption is needed!
  • 6. Layer 2 Data-Link Converts bits to frames Connects hosts in the LOCAL network No frames leave the local network Bridges between layers 1 and 3 No IPs, only MACs used between hosts ARP table MAC addresses globally unique * Broadcasts/Collisions Equipment Switches
  • 7. Layer 3 Network Converts Frame into a Packet by encapsulation Responsible for routing from source to destination Used to connect LOCAL networks together
  • 9. Troubleshooting Order network checklist Start by checking device registration Do you have a link? Can you ping the loopback 127.0.0.1 address? Can you ping the default gateway Do you have a valid IP? Can you tracert to an external IP address eg 8.8.8.8 (google) or yahoo.com?