Required firewall rules for the online responder (OCSP)

Implementing an online responder (OCSP) often requires planning the firewall rules to be created on the network. The following is a list of the required firewall rules and any pitfalls.

The Online Responder (Online Certificate Status Protocol, OCSP) is an alternative way of providing revocation status information for certificates. Entities that want to check the revocation status of a certificate do not have to download the complete list of all revoked certificates thanks to OCSP, but can make a specific request for the certificate in question to the online responder. For a more detailed description, see the article "Basics Online Responder (Online Certificate Status Protocol, OCSP)„.

Clients to the OCSP Responder

Clients address the online responder via unencrypted HTTP, accordingly only TCP port 80 must be opened.

Network protocol	Destination port	Protocol
TCP	80	Hypertext Transfer Protocol (HTTP)

OCSP Responder to the Certification Authority

Applies only if the online responder is a domain member.

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Quite analogous to all other clients are the certificate request ports to the certification authority to open. The online responder uses this to apply for its signature certificate.

Network protocol	Destination port	Protocol
TCP	135	RPC Endpoint Mapper
TCP	49152-65535	RPC dynamic ports

OCSP responder to the domain

Applies only if the online responder is a domain member.

The OCSP responder server is usually a domain member, so the general rules for domain communication apply here. In addition, since the online responder must actively request certificates, it must also be able to communicate with the domain.

Network protocol	Destination port	Protocol
TCP and UDP	53	Domain Name System
TCP	88	Kerberos
UDP	123	NTP
TCP	135	RPC Endpoint Mapper
TCP and UDP	389	LDAP
TCP	445	Server Message Block RPC Named Pipes
TCP	636	LDAP over SSL
TCP	3268	LDAP-GC
TCP	3269	LDAP-GC over SSL
TCP	49152-65535	RPC dynamic ports

Restore the default Windows Firewall rules

Enable-NetFirewallRule `
-Name "IIS-WebServerRole-HTTP-In-TCP".
Enable-NetFirewallRule `
-Name "IIS-WebServerRole-HTTPS-In-TCP".
Enable-NetFirewallRule `
-Name "Microsoft-Windows-OnlineRevocationServices-OcspSvc-DCOM-In".
Enable-NetFirewallRule `
-Name "Microsoft-Windows-CertificateServices-OcspSvc-RPC-TCP-In".
Enable-NetFirewallRule `
-Name "Microsoft-Windows-OnlineRevocationServices-OcspSvc-TCP-Out

Related links:

• Firewall rules required for Active Directory Certificate Services
• Required firewall rules for the Network Device Enrollment Service (NDES)
• Required Firewall Rules for Certificate Enrollment Policy (CEP) Web Service
• Required firewall rules for the Certificate Enrollment Web Service (CES)
• Required firewall rules for Certification Authority Web Enrollment (CAWE)