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copied!<p>You can use the following regular expressions separately or by combining them in a joint OR expression.</p> <pre><code>ValidIpAddressRegex = "^(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$"; ValidHostnameRegex = "^(([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]*[a-zA-Z0-9])\.)*([A-Za-z0-9]|[A-Za-z0-9][A-Za-z0-9\-]*[A-Za-z0-9])$"; </code></pre> <p><strong>ValidIpAddressRegex</strong> matches valid IP addresses and <strong>ValidHostnameRegex</strong> valid host names. Depending on the language you use \ could have to be escaped with \.</p> <hr> <p><strong>ValidHostnameRegex</strong> is valid as per <a href="http://tools.ietf.org/html/rfc1123" rel="noreferrer">RFC 1123</a>. Originally, <a href="http://tools.ietf.org/html/rfc952" rel="noreferrer">RFC 952</a> specified that hostname segments could not start with a digit.</p> <p><a href="http://en.wikipedia.org/wiki/Hostname" rel="noreferrer">http://en.wikipedia.org/wiki/Hostname</a></p> <blockquote> <p>The original specification of hostnames in <a href="http://tools.ietf.org/html/rfc952" rel="noreferrer">RFC 952</a>, mandated that labels could not start with a digit or with a hyphen, and must not end with a hyphen. However, a subsequent specification (<a href="http://tools.ietf.org/html/rfc1123" rel="noreferrer">RFC 1123</a>) permitted hostname labels to start with digits.</p> </blockquote> <pre><code>Valid952HostnameRegex = "^(([a-zA-Z]|[a-zA-Z][a-zA-Z0-9\-]*[a-zA-Z0-9])\.)*([A-Za-z]|[A-Za-z][A-Za-z0-9\-]*[A-Za-z0-9])$"; </code></pre>

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