Link Local Address

Link Local

• Denoted by FE80 prefix
  • Assign a single interface, multiple IPs
    • Follow by the keyword "secondary"
  • An OS in its default form, you are probably running IPv6, its on by default, in America you are less likely to not have IPv6 around.
  • Link Local allows you to communicate with other devices, it is not use for routable communications, it is for a dedicated style of communications on our local subnet but not further.
  • You could change the IP addresses and your routing won't change.
• Configured automatically in many devices
• EUI-64 supported but not required
  • Built the address bits based on your mac-address, which will make it unique.
  • The goal is to make a unique value, there is also a duplication check that we can do on the wire
• Unique value
• Locally (broadcast domain) significant

Link Local Example

• Separate broadcast domains (right and left)
• You could have the same FE80 address as long as they are in different subnets (broadcast domains).

Duplicate addresses

interface is noted with routing entries & neighbors to ensure proper delivery

Protocols That Leverage Link Local

• OSPFv3
  • Provides capabilities for IPv6 addressing
• EIGRP
  • Link local networks
• HSRP
  • High Standard Routing Protocol
• RIP-NG
  • Running on IPv6

EUI

• The host portion IPv6 addresses are created through a process called EUI-64
  • Divide the MAC address in half
  • Insert FFFE in between
  • Invert the 7th bit
• E8-84-A5-32-28-45
• E8-84-A5 | 32-28-45
• E8-84-A5-FF-FE-32-28-45
• E8