
Application Layer
Application Layer
Content
Content
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A Traditional Firewall
A Traditional Firewall
’
’
s View
s View
Of A Packet
Of A Packet
Only packet headers are inspected
Only packet headers are inspected
¾
¾
Application layer content appears as
Application layer content appears as
“
“
black box
black box
”
”
IP
IP
Header
Header
Source Address,
Dest. Address,
TTL,
Checksum
TCP
TCP
Header
Header
Sequence Number
Source Port,
Destination Port,
Checksum
Forwarding decisions based on port numbers
Forwarding decisions based on port numbers
¾
¾
Legitimate traffic and application layer attacks use identical p
Legitimate traffic and application layer attacks use identical p
orts
orts
Internet
Expected HTTP Traffic
Unexpected HTTP Traffic
Attacks
Non-HTTP Traffic
Corporate
Network
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