This is used to modify the IPv4 TTL header field. The TTL field determines how many hops (routers) a packet can traverse until it's time to live is exceeded.

Setting or incrementing the TTL field can potentially be very dangerous, so it should be avoided at any cost. This target is only valid in mangle table.

Don't ever set or increment the value on packets that leave your local network!

--ttl-set value
    Set the TTL value to `value'.

--ttl-dec value
    Decrement the TTL value `value' times.

--ttl-inc value
    Increment the TTL value `value' times.