netstat command is a mightly utility found in majority of Unix and Linux distributions.
Among other things like showing network routes and reporting network connections and ports, netstat can also report if your network interfaces have any trouble sending or receiving packets.
Report network errors with netstat
The basic format for this functionality is shown below:
greys@s5:~ $ netstat -ni
IMPORANT: always double-check the interface name you're checking. I have highlighted the physical interface in my example, because it's important: your virtual interfaces are unlikely to provide any useful network reliability info – so you always must be checking the primary, physical interfaces (or primary, virtual ones if you're looking at a VM).
No errors in RX-ERR (receive errors) or TX-ERR (send errors), which is pretty impressive for a dedicated server that's been online for a year:
greys@s5:~ $ uptime 17:34:30 up 366 days, 2:39, 1 user, load average: 0.11, 0.14, 0.19