Site Local Address - FC00::/7

Site local address is IPv6's counter part to IPv4's private address space (as defined in RFC 1918).  It is typically used within a site or organization.  This type of address is not globally routable meaning you can't access this type of address from the internet.

RFC 1884 reserved the block FEC0::/10 for site local address but this has since been deprecated and replaced with FC00::/7 for used in private networks as defined in RFC 4193.

FC00::/7 is further divided into two /8 subnets:
  • FC00::/8 - the usage of this block has not been clearly defined.
  • FD00::/8 - the routing prefix is formed by appending 40-bit of randomly-generated bit string in the format of FDxx:xxxx:xxxx::/48 leaving the network administrator with 16 bit for subnetting and 64 bit for network identifier.
Site local address can be identify by the first 8 bits of any given IPv6 address.  They should match either 11111100 or 11111101.

  • 8 bitsPrefix
  • 40 bitsrandom bit string
  • 16 bitsSubnet
  • 64 bitsInterface ID
  • FD
  • 00:F53B:82E4
  • 0000
  • 0000:0000:0000:0053

Click on this link to examine Site Local address using the Advanced Online IPv6 Subnet Calculator: FD00:F53B:82E4:0000:0000:0000:0000:0053