Novell NETWARE 6-DOCUMENTATION Manual page 1919

Figure 6 IP Packet Forwarding Filter Example
IP Network 159.3.0.0
Router C
IP Network 149.1.0.0
(FDDI Backbone)
FDDI_B
Router A Router B
External Internetwork
NE2000_B
IP Network 153.5.0.0
Mail Server
153.5.3.1
Because internal communication is not restricted, packet forwarding filters are
not required on Routers A or C.
Two packet forwarding filters are required on Router B. The first filter ensures
that any packet originating within the organization's internal networks are
forwarded by Router B. The second filter provides access to the corporate mail
server and allows external users to send and receive electronic mail to and
from internal users.
To configure the first filter, the source identifies the packets that originate in
the internal networks. The simplest way to do this on Router B is to identify
all packets received from the FDDI backbone interface. Because internal users
can use any service at any location, the remaining fields in the filter can be
specified as ANY.
The source of the second filter is all packets originating from external
networks. Because the interface NE2000_B is the only connection that Router
B has to the external networks, this can be used to specify the source field for
this filter. SMTP (Simple Mail Transfer Protocol) is selected from the
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