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In IPv6 SLAAC (stateless address autoconfiguration), how does a host create a global unicast address?

  1. AIt queries a DHCPv6 server and leases a 128-bit address managed by the server for a set period
  2. BIt combines the /64 prefix in the router advertisement (RA) sent by a router with an interface ID (the lower 64 bits) it creates itself, and uses the address after checking that no other device has the same address
  3. CIt puts its own IPv4 address as it is into the lower 32 bits and fills the upper bits with a value starting with fe80
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Answer: B. It combines the /64 prefix in the router advertisement (RA) sent by a router with an interface ID (the lower 64 bits) it creates itself, and uses the address after checking that no other device has the same address

With SLAAC, a host learns the prefix of its link (normally a /64) from the router advertisements (RAs) that routers send periodically or on request. It combines this with an interface ID, either in the EUI-64 format derived from its MAC address or based on a random value, to form an address. Before using it, the host uses Neighbor Discovery to check that no other device is using the same address (duplicate address detection, DAD). The link-local address of the router that sent the RA becomes the default gateway, and because no server manages the address assignments, it is called "stateless." DNS server addresses are provided by an RA option or by stateless DHCPv6.

  • A. This is address assignment by stateful DHCPv6.
  • B. Correct. It combines the RA prefix with an interface ID it creates itself.
  • C. No such method exists. Addresses starting with fe80 are link-local addresses, not global unicast addresses.
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