[Day 11] 7. Anycast Address

Definition

• An Anycast address is an IPv6 address that can be assigned to multiple interfaces. Packets sent to an Anycast address are routed to the nearest (in terms of routing distance) interface that has that address.

Use Case:

• Anycast is commonly used for services like DNS, where multiple servers may provide the same service, and clients are routed to the nearest one for efficiency.

EUI-64 Format

Definition:

• EUI-64 (Extended Unique Identifier) is a method to automatically generate a unique IPv6 interface identifier based on a device's MAC address. It expands the 48-bit MAC address into a 64-bit identifier by inserting
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  FFFE

  in the middle and inverting the 7th bit.

Example of Generating EUI-64:

1. MAC Address: Assume a MAC address of
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   00:1A:2B:3C:4D:5E

   .
2. Convert to EUI-64:
   • Split the MAC:
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     00:1A:2B

     and
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     3C:4D:5E

     .
   • Insert
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     FFFE

     :
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     00:1A:2B:FF:FE:3C:4D:5E

     .
   • Invert the 7th bit:
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     02:1A:2B:FF:FE:3C:4D:5E

     .

Example of Anycast Address with EUI-64

Assuming the Anycast address is

3A:2B1C::

/64

1. Anycast Address:

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   3A:2B1C::

2. Host Identifier Using EUI-64:

   • Generated from MAC
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     00:1A:2B:3C:4D:5E

     results in
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     3A:2B1C:02:1A:2B:FF:FE:3C:4D:5E

     .

3. Final Anycast Address:

   • The complete Anycast address for a device could be
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     3A:2B1C:02:1A:2B:FF:FE:3C:4D:5E

     .

Summary

• Anycast addresses are useful for routing to the nearest service instance, while EUI-64 simplifies the creation of unique identifiers for interfaces based on MAC addresses. This combination enhances network efficiency and device identification.