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Network Firewalls   «Prev 

Packet Screening

Packet screening
Packet screening
Hot spot 1 The packet filter tells the router to filter the content of IP packets based on the source IP address, destination IP address, TCP/UDP source port, and TCP/UDP destination port fields.
Hot spot 2 In packet filtering, the rules are executed sequentially. Once a packet has failed any portion of a filter, the subsequent rules will not be read.
Hot spot 3 The allow action routes the packet as normal if all conditions within the rule are met. The block action discards all packets if the conditions in the rule are not met. Packet filters discard any packet unless it has specifically been allowed within a rule.
Hot spot 4

Rule 1 allows any host with the network address 192.168.10.0 to initiate a TCP session on any destination IP address on port 21.
Hot spot 5

The second rule blocks any packet originating from any remote address with a source port of 20 and contacting a host with a network address 192.168.10.0 on any port less than 1024. If any packet meets the conditions of rule 2, it will be immediately discarded, and rule 3 will never be executed
Hot spot 6

The third rule allows any remote address that has a source port of 20 and is contacting any host with a network address of 192.168.10.0 on any port. Rule 3 is necessary because packet filters work by excluding all inbound and outbound traffic unless such traffic has been specifically allowed by a rule.