I'm the host for a two-/three-player private vanilla-modded server, and we just recently finished Day 28. There was a large amount of complaint from the other two players that they were lagging to hell and back.

When everything's working "fine", the pings are usually at most 150ms, but when the brown matter hits the blades, there could be pings upwards of 30 seconds, even so high it overflowed back into the negative. Good on the Pimps for using shorts for the ping, points off for using signed shorts.

I have a "fancy" G510s keyboard with a display, and a background app I run using that display said I was barely even using 250Kbps of my 2Mbps outbound connection, but I did note that my CPU was getting downright hammered, barely dipping below 75%.

I have a GTX 980, an i5 4590 (quad, no ht) clocked at 3.30 GHz, and my Internet has been consistently clocked at 20Mbps down, 2Mbps up when working properly. The issue has arisen several times over different days, so I'm not willing to blame it on ISP spottiness.

EDIT1: I almost forgot. Symptoms of the lag include: non-host users getting delayed (by up to a minute) hits, not getting live updates of zombie locations. Time going slow, catching up by the time the horde's over.

Meanwhile, the host is getting beat upon at a buttery 60 FPS. what