Lantronix LSB4, Руководство по установке

Страница: 46 / 91

Set-up and Operation LSB4 Installation Guide
3-18
Introduction
Set-up and
Operation
Filter Configuration
When a packet is received at an LSB4 port, the source and destination ad-
dresses of the packet are compared. If the address of the source and desti-
nation of a packet are the same, the packet is presumed to be at its final
destination and doesn't need to travel any further. Once it is determined
that a packet is
not at its destination (the source and destination addresses
do not match), a packet may then be subject to any existing filters .
Filters are used to permit or deny passage of data packets through the
LSB4. The
Set Filter and Define Filter commands are used to specify fil-
ters. Related filter commands are Show/List Filters and Clear/Purge Fil-
ters .
Creating a “Firewall”
A firewall is often used to prevent all but one type of traffic (for example,
traffic from a specific node) from reaching a particular network segment.
When traffic destined for a specific segment reaches the LSB4, it will be
compared to a list of
filters ; if it is any but a specified type of traffic, it hits
a ÒfirewallÓ and goes no further--the packet is discarded.
The commands listed below [Figure 3-21] create a firewall between LAN
1 and any other network segment. Filter 1 is configured to deny access to
IP packets; this filter is assigned to port 1, preventing IP packets from trav-
eling from port 1 to other segments.
Figure 3-21: Preventing IP Traffic Out of Port 1
Figure 3-21 included a Set Privileged command before the Set Filter
command. The Set Filter command requires privileged status; if privi-
leged status is currently enabled, the Set Privileged command will not be
necessary.
Local_1> SET PRIVILEGED
Local_1> SYSTEM (not echoed)
Local_1>> SET FILTER 1 APPEND PROTOCOL IP DENY
Local_1>> SET SWITCH ETHERNET 1 FILTER 1
NOTE