User`s guide

Defining Filters and Firewalls
Filter persistence
6-36 Preliminary January 30, 1998 Pipeline User’s Guide
1
Create a firewall filter using SAM.
2
Download it to the Pipeline.
3
Open Ethernet > Mod Config > Ether Options.
4
Enter the number of the firewall filter you want to use in the Filter field.
This number is derived from the number in the Firewall menu. For example,
if the firewall is number 20-503, enter number 103 in the Data Filter field.
5
Exit and save the profile.
Filter persistence
A Filter persistence parameter is present in Connection profiles of all Pipelines
that support Filter Profiles. The Filter Persistence parameter must be set to Yes to
allow a connection’s firewalls to persist when the connection is torn down, such
as by connection timeout. The default is No, implying that, by default,
connection firewalls do not persist when a call is terminated.
Note:
Typically a firewall will persist for about an hour after its associated
connection has been torn down.
Background on firewall and filter persistence
The idea of filter persistence is intended to allow a Pipeline to preserve its filter
or firewall specifications throughout the lifetime of its connections.
Firewalls differ from filters in that firewalls are designed to alter their behavior as
traffic passes through them, but filters remain unchanged through their lifetimes.
Filters provide for the construction and destruction of filters whenever the state of
a connection changes, which causes the Pipeline to create and destroy filters
during connection state changes without any reference to the state of the filters.
When Secure Access Firewalls are present, it is necessary to preserve the firewall
state across the many transitions that connections may experience. Where filters
can be built or destroyed at any time to accommodate changes due to Multilink
and idle-inactivity conditions, firewalls cannot.