When in standard FTP mode, the inside client initiates the control connections to the FTP server and the server initiates the data connections. You use the fixup protocol ftp 21 command to allow the PIX to create a dynamic return connection for the data returning from the server.
When in passive FTP mode, the inside client initiates both the control and data connections, so the ASA will allow return traffic through the PIX without a need for the fixup protocol ftp 21 command.
The show fixup command displays the active fixup protocols on the PIX firewall.
The PIX supports the SCCP, Skinny, SIP, and H.323 VoIP protocols.
RTSP is a real-time audio and video protocol used by several multimedia applications, such as RealPlayer, Cisco IP/TV, Quicktime 4, Netshow, and VDO live. The fixup protocol rstp command enables RTSP support for NAT only.
WebSense and N2H allow URL traffic filtering when fixup protocol HTTP 80 is enabled.
The filter URL command is used to identify which traffic you want to forward to the URL servers.
The PIX firewall can be a DHCP client and a DHCP server at the same time.
The dhcpd dns command allows you to set only two DNS server IP addresses.
When configured, PPPoE can connect to the service providers without user interaction.