IV. server placement (cont.): measurements

dns clients list
Goal: representative list to run on all skitter monitors
combine individual clients lists from all root name servers
stratify IPv4 address prefix space
prefix - independently routable slice of address space
no more than 150K destinations
so that we can probe 3-5X/day (less sensitive to diurnal variations)

current dns clients list created in March 2002
passive collection of addresses at 7 root servers
select one host per routable /24 prefix 
prefer hosts seen by most root servers
                 
nearly 2M addresses passively collected from root servers
selected more than 143K addresses
cover about 50% of prefixes from the global BGP table