iptables
https://linux.die.net/man/8/iptables

Administration tool for IPv4/IPv6 packet filtering and NAT


Examples

Configure iptables to count incoming and outgoing traffic from/to given IP

iptables -I INPUT 1 -s <IP> -j ACCEPT
iptables -I OUTPUT 1 -d <IP> -j ACCEPT

Reset counters

iptables -Z