CCNA-Notes/06. Ethernet LAN Switching (part 2).md

id, aliases, tags

id	aliases	tags
06. Ethernet LAN Switching (part 2)		CCNA

Ethernet LAN Switching (part 2)

Ethernet Frame

• The preamble + SFD is usually not considered part of the Ethernet header
• therefore the size of the Ethernet header + trailer is 18 bytes (6+6+2+4)
• the minimum size for an Ethernet frame (Header + payload (Packet) + trailer) is 64 bytes
• 64 bytes - 18 bytes (header + trailer size) = 46 bytes
• therefore the minimum payload (packet) size is 46 bytes
• if the payload is less than 46 bytes, padding bytes are added
• ie. 34-byte packet + 12-byte padding = 46 bytes

ARP

• ARP stands for 'Address Resolution Protocol'
• ARP is used to discover the Layer 2 address Mac address of a known Layer 3 address IP address
• Consists of two messages:
  • ARP Request
    • ARP Request is broadcast = sent to all hosts on the network
  • ARP Reply
    • ARP REply is unicast = sent only to one host (the host that sent the request)

ARP Table

• command to view the ARP table
  • use arp -a (Windows, macOS, Linux)
  • use show arp (Cisco devices)
• Internet Address = IP address (layer 3 address)
• Physical Address = MAC address (layer 2 address)
• type static = default entry
• type dynamic = learned via ARP

Ping

• A network utility that is used to test reachability
• Measures round-trip time
• Uses two messages
  • ICMP Echo Request
  • ICMP Echo Reply
• command to use pin: ping (ip-address)

MAC address table

command to view it

• show mac address-table

SW1#show mac address table

Vlan  Mac Address     Type    Ports
----  -----------     ----    -----
   1  0c2f.b011.9d00  DYNAMIC Gi0/0
   1  0c2f.b06a.3900  DYNAMIC Gi0/2

Total Mac addresses for this criterion: 2

• Vlan : Virtual local area network
• Ports = Interface

Clearing the Mac address Table

for manually remove mac address table use this command

• clear mac address-table dynamic for just one mac address
• clear mac address-table dynamic address (mac address)
• clear mac address-table dynamic address 0c2f.b06a.3900 for one interface
• clear mac address-table dynamic interface (interface)
• clear mac address-table dynamic interface Gi0/0

Summary

• Ethernet frame payload minimum size
• ARP (Address Resolution Protocol)
  • ARP Request
  • ARP Reply
• ARP table
• Ping
  • ICMP Echo Request
  • ICMP Echo Reply
• Mac Address Table