A common way to measure network latency to a remote host is by using ping utility which uses ICMP echo request and reply packets. In some cases, however, ICMP traffic is blocked by firewalls, which renders ping utility useless with hosts behind restrictive firewalls. In such case, you will need to rely on layer-3 measurement tools that use TCP/UDP packets since these layer-3 packets are more likely to bypass common firewall rules.
One such layer-3 measurement tool is tcpping. To measure latency, tcpping takes advantage of so-called half-open connection technique, based on TCP three-way handshake. Continue reading »