Posted on by Glenn

Network+ : Ethernet Basics

  1. Network+ Certification (N10-007): Syllabus
  2. Network+ : Introductions and Resources
  3. Network+ : Network Models
  4. Network+: Cabling
  5. Network+ : Topologies
  6. Network+ : Ethernet Basics
  7. Network+ : Contemporary Ethernet
  8. Network+ : Installing a Physical Network
  9. Network+ : Booting and Getting On the Network
  10. Network+ : TCP/IP Basics
  11. Network+ : Subnetting
  12. Network+: Routing Protocols
  13. Network+ : Routing and Firewalls
  14. Network+ : TCP/IP Ports and Applications
  15. Network+ : Network Naming and Sharing Resources
  16. Network+ : Secure Networking
  17. Network+ : Advanced Networking Devices
  18. Network+ : IPv6
  19. Network+ : Remote Connectivity
  20. Network+ : WiFi
  21. Network+ : Virtualization
  22. Network+ : Mobile Networking
  23. Network+ : Building a Real-World Network
  24. Network+ : Managing Risk
  25. Network+ : Protecting Your Network
  26. Network+ : Network Monitoring
  27. Network+ : Network Troubleshooting
  28. Network+: Network Monitoring

Unit 6

Chapter 3

MAC Discovery and Resolution

Ethernet uses frames (with MAC addresses in the headers).

The Broadcast MAC address for local, Ethernet networks is

ff:ff:ff:ff:ff:ff

(12 Fs, or 12 nybbles, or 48 bits).

At boot, your PC sends a frame to the ethernet broadcast, from its MAC address. The nearest switch detects this broadcast and maps your MAC address to the physical port you’re plugged into. Now it can send traffic bound to you out the correct port.

Resolving MAC Addresses to IP Addresses

We do this only on local networks. Local Ethernet cares about your MAC address, but nothing outside your router does, except aspiring hackers. That’s why you’ll blur our MAC addresses in images you post.

The Address Resolution Protocol (ARP) makes the magic happen, resolving MAC to IP. It keeps a cache of addresses it’s already looked up, which you can see, and possibly delete, with these two commands.

arp -a
arp -d *

Notice how deleting the cache requires Admin permissions, so kiddies with a copy of Ettercap can’t quite so easily hack your ARP table – though they will still be able to do it.

Parts of an Ethernet frame: https://www.techwalla.com/articles/what-is-an-ethernet-preamble