С использованием класса Group из исходной строки нужно выбрать все подстроки - C#

string text = "For example, an IPv4 address and its subnet mask may be 192.0.2.1 and 255.255.255.0, respectively. The CIDR notation for the same IP address and subnet is 192.0.2.1/24, because the first 24 bits of the IP address indicate the network and subnet.";
foreach (Match m in Regex.Matches(text, @"\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}"))
{
    Group grp = m.Groups[0];
    Console.WriteLine(grp.Value);
}