/etc/sysctl.conf #
Contains settings for configurations in the /proc/sys directory that are applied at boot time. For example, /proc/sys/net/ipv4/ip_forward can be set to 1 at boot time by adding an entry net.ipv4.ip_forward= 1 to this file.
/proc/net/ip_conntrack #
Dumps the contents of the connection tracking structures if you read it.
/proc/sys/net/ipv4/ip_conntrack_max #
Controls the size of the connection tracking table in the kernel. The default value is calculated based on the amount of RAM in your computer. You may need to increase it if you are getting “ip_conntrack: table full, dropping packet” errors in your log files. See also the entry for /etc/sysctl.conf in this table.
/proc/sys/net/ipv4/ip_forward #
You need to set this to 1 for the host to act as a gateway (forwarding packets among the networks connected to its interfaces).