Chapter 25 ALG Screen

25.1.3 ALG and Multiple WAN

When the ZyWALL has two WAN interfaces and uses the second highest priority WAN interfaces as a back up, traffic cannot pass through when the primary WAN connection fails. The ZyWALL does not automatically change the connection to the secondary WAN interfaces.

If the primary WAN connection fails, the client needs to re-initialize the connection through the secondary WAN interfaces to have the connection go through the secondary WAN interfaces.

When the ZyWALL uses both of the WAN interfaces at the same time, you can configure routing policies to specify the WAN interfaces that the connection’s traffic is to use.

25.2 FTP

File Transfer Protocol (FTP) is an Internet file transfer service that operates on the Internet and over TCP/IP networks. A system running the FTP server accepts commands from a system running an FTP client. The service allows users to send commands to the server for uploading and downloading files. The FTP ALG allows TCP packets with a port 21 destination to pass through. If the FTP server is located on the LAN, you must also configure NAT port forwarding and firewall rules if you want to allow access to the server from the WAN.

25.3 H.323

H.323 is a standard teleconferencing protocol suite that provides audio, data and video conferencing. It allows for real-time point-to-point and multipoint communication between client computers over a packet-based network that does not provide a guaranteed quality of service. NetMeeting uses H.323.

25.4 RTP

When you make a VoIP call using H.323 or SIP, the RTP (Real time Transport Protocol) is used to handle voice data transfer. See RFC 1889 for details on RTP.

25.4.1H.323 ALG Details

•The H.323 ALG supports peer-to-peer H.323 calls.

•The H.323 ALG handles H.323 calls that go through NAT or that the ZyWALL routes. You can also make other H.323 calls that do not go through NAT or routing. Examples would be calls between LAN IP addresses that are on the same subnet.

•The H.323 ALG allows calls to go out through NAT. For example, you could make a call from a private IP address on the LAN to a peer device on the WAN.

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ZyWALL 2WG User’s Guide