Circuit Gateway - Planet GRT-504 User Manual

192.168.0.10
192.168.0.11
Internal/Protected Network
192.168.0.10:1025
192.168.0.11:4406
Internal/Protected Network

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
GRT-504 4-Wire G.SHDSL.bis Firewall Router User's Manual
NAT (Network Address Translation)
Firewall
192.120.8.5
Internal IP External IP
192.168.0.10 192.120.8.5
192.168.0.11 192.120.8.5
PAT (Port Address Translation)
Firewall
192.120.8.5
192.120.8.5:2205
192.120.8.5:2206
Client IP Internal Port
192.168.0.10 1025
192.168.0.11 4406
destination IP address and/or port
source IP address and/or port
time of day
protocol
user
password
17
Internet
External/Unprotected Network
Internet
External Port
2205
2206
External/Unprotected Network