https://blog.gongquiz.com/2021/01/14/%eb%8b%a4%ec%9d%8c-ipv4%ec%9d%98-b-%ed%81%b4%eb%9e%98%ec%8a%a4-%eb%8c%80%ec%97%ad%ec%97%90-%ed%95%a0%eb%8b%b9%eb%90%9c-%ec%82%ac%ec%84%a4-ip-%ec%a3%bc%ec%86%8c%ec%9d%98-%eb%b2%94%ec%9c%84%eb%a1%9c/