pkKumar - 7:07 am on Jan 8, 2013 (gmt 0)

well isapi is not an option specially with shared hosting server. I didn't find anything here but according to a blog we can do that with request filtering in web.config like this.
<requestFiltering>
<filteringRules>
<filteringRule name="Block bot" scanUrl="false" scanQueryString="false">
<scanHeaders>
<add requestHeader="user-agent" />
</scanHeaders>
<appliesTo />
<denyStrings>
<clear />
<add string="googlebot" />
</denyStrings>
</filteringRule>
</filteringRules>
</requestFiltering>

For IP it has:
<ipSecurity allowUnlisted="true">
<clear/>
<add ipAddress="111.111.111.111"/> <!-- Blocks a specific IP. -->
<add ipAddress="222.222.222.0" subnetMask="255.255.255.0"/> <!-- Blocks entire subnet. -->
</ipSecurity>

Has anybody tried that ?