User`s guide

Defining Filters and Firewalls
Working with predefined call filters
Pipeline User’s Guide Preliminary January 30, 1998 6-21
The second Input filter specifies TCP packets, Protocol=6, from any address and
to any address and forwards them if the destination port is greater than the source
port. For example, Telnet requests go out on port 23 and responses come back on
some random port greater than port 1023. So, this filter defines packets coming
back to respond to a user's request to Telnet, or to other requests using the TCP
protocol, to a remote host.
The third Input filter specifies UDP packets, Protocol=17, with exactly the same
situation as described above for Telnet. For example, a RIP packet is sent out as a
UDP packet to destination port 520. The response to this request also is sent to a
random destination port greater than 1023.
Finally, the fourth Input filter specifies unrestricted pings and traceroutes. ICMP
does not use ports like TCP and UDP, so a port comparison is unnecessary.
Working with predefined call filters
The Pipeline ships with three predefined Filter profiles, one for each commonly
used protocol suite.
• IP Call, for IP connections
• NetWare Call, for IPX connections
• AppleTalk Call, for bridged AppleTalk connections
These predefined filters are intended as call filters, to help keep connectivity
costs down. They provide a base that you can build on to fine-tune how the
Pipeline handles routine traffic on your network.
Note:
You can modify the predefined Filter profiles to make them more full-
featured for the types of packets commonly seen on your network that you want
to prevent from initiating or maintaining connections.
NetWare Call filter
The predefined NetWare Call filter is designed to prevent Service Advertising
Protocol (SAP) packets originating on the local IPX network from resetting the
idle timer or initiating a call.