The Barracuda NG Firewall generally provides three different ways of dealing with RPC services:
- Advantage: The firewall immediately notices RPC port changes (traffic analyzes client – server).
- Disadvantage: The firewall notices the RPC port which is used only on client requests. If a firewall reboot occurs, the firewall will not know the port until the next client request gets scanned.
The term PASSIVE means in this case "sniffing" RPC information passively. Using this type causes that the firewall engine reads the RPC information from RPC requests (using UDP/TCP on port 135 (DCERPC) or port 111 (OCNRPC)) automatically using the plugin DCERPC or OCNRPC. This way you are benefiting from the fact that the firewall is always up-to-date on the currently valid ports. The main problem of passive configuration is that in case of a reboot of the firewall there would not be any information concerning the required ports as the information is not written to disk. Clients attempting to use previously established RPC connections would be blocked.
- Advantage: The firewall actively looks for all RPC information independent of client requests.
- Disadvantage: All RPC servers are to be configured manually. Port changes within a polling interval will not be recognized by the firewall.
The term ACTIVE means in this case requesting RPC information actively. This method uses a defined RPC server where the firewall obtains the RPC information periodically. A benefit of this type is that the firewall knows the type of services available on the RPC server. However, problems may occur if the RPC server is not available for some time. In this case the RPC server may have new portmapping information as soon as it is online again but the firewall still uses the "old" information as valid ones which leads to blocked connection attempts.
Active & Passive
ACTIVE and PASSIVE at the same time is combining the benefits of both and is therefore recommended.
For detailed information on how to configure RPC plugins, see:
The monitoring of RPC takes place in the Dynamic Services tab of the Barracuda NG Firewall box menu entry (tab Dynamic):
- Go to the Dynamic page (FIREWALL > Dynamic).
- Click on the Dynamic Services tab.
Right click and select Trigger Update of RPC Server Information to refresh the displayed content.
Every RPC Connection is displayed with the following information:
- Used Address – IP address used by the dynamic service.
- Proto – Protocol used by the dynamic service.
- Port – Port used by the dynamic service.
- Service Name – Name and Number of the dynamic service.
- Service Desc – Description for the dynamic service.
- Target Address – IP address where the dynamic service connects to.
- Expires – Displays when the dynamic service connection expires.
- Used – Expired time since last usage.
- Updated – Expired time since last information update.
- Source Address – IP address for which the dynamic service entry is valid for (entry 0.0.0.0 indicates all IP addresses).
- Source Mask – Netmask which the dynamic service entry is valid for.