NetComm NB712 manual Types of Firewall, Packet Filtering, There are three types of firewall

2.1 Types of Firewall

There are three types of firewall:

2.1.1 Packet Filtering

In packet filtering, only the protocol and the address information of each packet is examined. Its contents and context (its relation to other packets and to the intended application) are ignored. The firewall pays no attention to applications on the host or local network and it “knows” nothing about the source of the incoming data. Filtering consists of examining incoming or outgoing packets and allowing or disallowing their transmission on the basis of a set of configurable rules. Network Address Translation (NAT) routers offer the advantages of packet filtering firewalls but can also hide the IP addresses of computers behind the firewall, and offer a level of circuit-based filtering.

Level 5: Application

Protocol

Level 4: TCP		Source/Destination address
Level 3: IP		Source/Destination port
		IP options
Level 2: Data Link		Connection status
Level 1: Physical
192.168.0.5	172.16.3.4
Firewall
Filter remembers
this information
UDP
SP=3264
SA=192.168.0.5
DP=1525
DA=172.16.3.4
Matches outgoing
so allowed
UDP
SP=1525
SA=172.16.3.4
DP=3264
DA=192.168.0.5
No matches
so disallowed
UDP
SP=1525
SA=172.168.3.4
DP=2049
DA=192.168.0.5
192.100.0.10:1025
		192.120.8.5:2205	Internet
		192.120.8.5:2206
Firewall 192.120.8.5
Client IP		Internal Port	External Port
192.100.0.11:4433		1025	2205
192.68.0.10
192.168.0.11		4406	2206
Internal/Protected			External/Unprotected
Network			Network

NB712 /	NB714 User Guide	9
YML829	Rev1