Aggregator

TLA (Top Level Aggregator)
/16
Big ISPs or IXes
8,192 (16 - 3 = 13 bit)
MUST announce /16 routing information to other TLAs

NLA (Next Level Aggregator)
/17 - /48
Medium or small ISPs
NLA1, NLA2,...
Final NLA is a site

SLA (Site Level Aggregator)
/49 - /64
Subnet number in a site
65,536 subnets per site
3ffe:501:8:1234:260:97ff:fe40:efab