The Online Responder Web proxy cache represents the service interface for the Online Responder. It is implemented as an Internet Server Application Programming Interface (ISAPI) extension hosted by Internet Information Services (IIS), and it performs the following operations:

  • Request decoding. After a request is received by the Online Responder Web proxy, the decoder component will try to decode the request and extract the certificate serial number to be validated.

  • Response caching. After a request is received and a certificate serial number is extracted, the Online Responder Web proxy will check the local cache for a valid response. The cache item validity period is set by default to the certificate revocation list (CRL) validity period from which the response was generated.

You can modify the following Web proxy–related settings for an Online Responder:

  • Web proxy threads. This setting refers to the number of threads that will be allocated by the Online Responder ISAPI extension for handling requests. Increasing the number of threads will use more of the server's memory and reducing the number of threads will reduce the number of clients that can be served concurrently.

  • Cache entries allowed. The cache is implemented as part of the Online Responder's ISAPI extension and is an in-memory cache only. The recommended cache size is between 1,000 and 10,000 entries. The minimum cache entries allowed is five. A small cache size will cause more cache faults and will result in a higher load on the Online Responder service for lookup and signing operations; a large cache size will increase the Online Responder's memory usage.

You must have Manage Online Responder permissions on the server hosting the Online Responder to complete this procedure. For more information about administering a public key infrastructure (PKI), see Implement Role-Based Administration.

To modify the Online Responder Web proxy
  1. Open the Online Responder snap-in, and select the Online Responder.

  2. Click Responder Properties on the Action menu, or click Responder Properties in the Action pane.

  3. Click the Web Proxy tab, modify the Web proxy options that you want to change, and then click OK.

Additional references