Enabling this directive instructs Squid to ask its neighbors for their ICMP measurements, which are included in ICP/HTCP replies. This, essentially, populates your netdb database with your neighbors’ ICMP measurements. The bulk “netdb exchange” is another way to receive those measurements (see Section 10.5).
Squid uses the neighbors’ netdb
measurements when making forwarding decisions. If one of the parents
is closer to the origin server, Squid forwards the request there and
marks it with