private address use Internet is partitioned by > 2 layers of NAT private addresses = 1.7% of skitter replies (18K out of 1.07M, Jul.02-31,2001) assumption: private IPs are misconfigs we assume a generic misconfig rate of 1% inadvertent transit ASes: 1.25% multi-origin prefixes: 1.3% (assume 100x more private addrs than we observe) => private/unique IPs ~ 1.7 (order of magnitude)