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  "description": "PIX Protocol Handling and Fixup commands.",
  "path": "/pix-protocol-handling/",
  "publishedAt": "2026-02-07T17:00:02.000Z",
  "site": "https://cg1network.com",
  "tags": [
    "SIP",
    "MGCP"
  ],
  "textContent": "  * Many popular protocols and applications will assign ports or addresses dynamically (Multimedia, P2P File Sharing, HTTP, FTP, SQL*Net)\n  * Some apps embed port data into upper layers\n  * PIX can manage negotiated ports and addresses for end-to-end sessions through the firewall\n  * Utilizes NAT-relevant addressing in packets as well as PAT\n  * Inspects packets for improper use of apps and services\n  * PIX can be configured to allow inspected apps or protocols to traverse through dynamic stateful changes\n\n\n\nAn FTP (Active Mode) server uses different ports for control (client-initiated) and data (server-initiated) connections. The fixup command will temporarily allow an inbound data channel connection for the duration of the control session. FTP in passive mode, both channels are requested by the client.\n\nFixup protocols enabled by default on default ports: FTP, SMTP, HTTP, RSH, RTSP, SQL*Net, H.323, ILS, SCCP, SIP, CTIQBE, MGCP.\n\n\n    fixup protocol ftp 2021 strict\n\nRemote Shell (RSH) client-initiated TCP command channel, server-initiated TCP Error connection channel.\n\n\n    fixup protocol rsh 1540\n\nSQL*Net uses a single channel but can be redirected to a different port or secondary server.\n\n\n    fixup protocol sqlnet 66\n\n### DNS Fixup\n\nPIX firewall 6.2 or higher supports NAT’s embedded IP Address within the DNS response packet.\n\nDNS queries will have 1 answer and 1 response\n\nPIX DNS fixup monitors all UDP transactions on port 53\n\nDNS request opens a response connection slot, and closes the slot after the answer is received\n\nCan perform translation of embedded IP Address using DNS record translation, alias command is needed prior to 6.2\n\n\n    alias (inside) 10.0.0.10 8.8.8.8 255.255.255.255\n\n### Multimedia Support\n\nMultimedia apps transmit on TCP, receive on TCP/UDP, and utilize dynamic ports.\n\nPIX firewall opens/closes ports dynamically and supports multimedia with/without NAT\n\nRTSP is used by many multimedia applications\n\n  * well-known TCP port 554\n  * Transport options are RTP and RDT (1st channel)\n  * RTCP or UDP resend (2nd channel)\n\n\n\nPIX supports the following RTSP applications\n\n  * Cisco IP/TV\n  * Apple QuickTime 4\n  * Real Networks (RealAudio, RealPlayer)\n  * RealServer\n\n\n\n\n    fixup protocol rtsp PORT\n    fixup protocol h323 PORT\n    fixup protocol mgcp PORT\n    fixup protocol ctiqbe 2748\n    fixup protocol skinny PORT\n    fixup protocol sip PORT",
  "title": "PIX - Protocol Handling",
  "updatedAt": "2026-02-07T17:00:02.000Z"
}