Planet Technology G.SHDSL.bis Bridge Router GRT-504 - Manual (Page 18)

GRT-504 4-Wire G.SHDSL.bis Firewall Router User’s Manual
Internet
192.168.0.10
192.168.0.11
192.120.8.5
Firewall
Internal/Protected Network External/Unprotected Network
NAT (Network Address Translation)
192.168.0.10
192.168.0.11 192.120.8.5
192.120.8.5
Internal IP External IP
Internet
192.168.0.10:1025
192.168.0.11:4406
192.120.8.5
Firewall
Internal/Protected Network External/Unprotected Network
PAT (Port Address Translation)
192.168.0.10
192.168.0.11
1025
4406
Client IP Internal Port External Port
2205
2206
192.120.8.5:2205
192.120.8.5:2206
3.2.2 Circuit Gateway
Also called a "Circuit Level Gateway," this is a firewall approach, which validates connections
before allowing data to be exchanged. What this means is that the firewall doesn't simply allow or
disallow packets but also determines whether the connection between both ends is valid according
to configurable rules, then opens a session and permits traffic only from the allowed source and
possibly only for a limited period of time.
Level 5: Application
Level 4: TCP
Level 3: IP
Level 2: Data Link
Level 1: Physical
destination IP address and/or port
source IP address and/or port
time of day
protocol
user
password
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