RFC 4193 defines a globally unique address that is used for local communications. For instance, they are routable within a specified site or between sites. These ULAs are similar to private addresses in IPv4 (RFC 1918).
Of the 128 bits available in IPv6 address, the last 64-bits are used as the interface ID.
The remaining 64 bits are used as follows:
First 8 bits are used to define the known prefix FC00::/7 or FD00::/7
40 bits - global ID - Generated using a random algorithm specified in the RFC 4193. EXOS expects the operator to specify the 40-bit Global ID as ULA address management becomes easier, especially a mult-vendor environment.
16 bits - Used to create subnets within the site.
ULA prefixes should not be accepted by the border routers.
Additionally, ULA prefixes should not be advertised by the border routers. In ExtremeXOS, for BGP (Border Gateway Protocol) and OSPFv3 (Open Shortest Path First version 3), you must specify the policies to filter ULA prefixes.
Here is an example of the command:
configure vlan v1 ipaddress fd21:0941:2c55::/48
The scope of ULA is global by default in RFC 4193.
All applications treat these addresses in a similar manner as any other type of global IPv6 unicast addresses.
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