Internet Security Firewalls

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Transcription:

Overview Internet Security Firewalls Ozalp Babaoglu! Exo-structures " Firewalls " Virtual Private Networks! Cryptography-based technologies " IPSec " Secure Socket Layer ALMA MATER STUDIORUM UNIVERSITA DI BOLOGNA Babaoglu 2001-2009 Sicurezza 2 Firewall Firewall! More like a moat around a medieval castle " restricts entry to carefully controlled points " prevents attackers from getting close to defenses " restricts exits to carefully controlled points! Combination of hardware and software to regulate traffic between an internal network and an external network (Internet)! Benefits of being connected while minimizing the risks of threats Babaoglu 2001-2009 Sicurezza 3 Babaoglu 2001-2009 Sicurezza 4

Firewall Firewall! What can a firewall do? " Focus security decisions " Enforce security policies " Log Internet activity! What can t a firewall do? " Protect against malicious insiders " Protect against connections that bypass it " Protect against completely new threats " Protect against viruses and worms " Set itself up correctly! Problems with firewalls " Interfere with the Internet end-to-end communication model " Create false sense of perfect security " Increase inconvenience for users Babaoglu 2001-2009 Sicurezza 5 Babaoglu 2001-2009 Sicurezza 6 Firewall Technologies Packet Filtering! Packet filtering! Proxy servers! Network address translation! Virtual Private Networks! Implemented through a screening router " Router: can the packet be routed to its destination? " Screening router: should the packet be routed to its destination?! Decision based on information in the IP packet header " IP source address " IP destination address " Protocol (TCP, UDP, ICMP) " Source port number " Destination port number " Packet size Babaoglu 2001-2009 Sicurezza 7 Babaoglu 2001-2009 Sicurezza 8

Packet Filtering Packet Filtering! Additional information " Interface the packet arrives on " Interface the packet will go out on! State information " Is the packet a response to an earlier packet? " Number of recent packets seen from the same host " Is the packet identical to a recently seen packet? " Is the packet a fragment? Babaoglu 2001-2009 Sicurezza 9 Babaoglu 2001-2009 Sicurezza 10 Packet Filtering Proxy Servers! Advantages " One screening router can protect the entire network " Extremely efficient " Widely available! Disadvantages " Hard to configure " Reduces router performance " Limited in the range of policies that can be implemented! Specialized application programs for Internet services (HTTP, FTP, telnet, etc.) " Proxy server " Proxy client! Need a mechanism to restrict direct communication between the internal and external networks! Typically combined with caching for performance Babaoglu 2001-2009 Sicurezza 11 Babaoglu 2001-2009 Sicurezza 12

Dual-Homed Host Proxy Servers Proxy Servers! Advantages " Can perform user-level authentication " Can do intelligent (application specific) filtering " Can be combined with caching " Can do good logging! Disadvantages " Typically lag behind their nonproxied equivalents " Require different servers for each service " Require modifications to clients Babaoglu 2001-2009 Sicurezza 13 Babaoglu 2001-2009 Sicurezza 14 Network Address Translation Network Address Translation! Allows a network to use a set of addresses internally and a different set of addresses externally! Invented not for security but for conserving IP addresses! Typically implemented within a router Babaoglu 2001-2009 Sicurezza 15 Babaoglu 2001-2009 Sicurezza 16

Network Address Translation Firewall Architectures! Advantages " Enforces firewall control over outbound traffic " Restricts incoming traffic (no spontaneous connections) " Hides structure and details of internal network! Disadvantages " Interferes with some encryption-based techniques " Dynamic allocation of addresses interferes with logging " Internal network cannot host externally-visible services (requires port mapping)! Screening Router! Dual-Homed Host! Screened Host! Screened Subnet Babaoglu 2001-2009 Sicurezza 17 Babaoglu 2001-2009 Sicurezza 18 Screening Router Dual-Homed Host Babaoglu 2001-2009 Sicurezza 19 Babaoglu 2001-2009 Sicurezza 20

Screened Host Screened Subnet DMZ Babaoglu 2001-2009 Sicurezza 21 Babaoglu 2001-2009 Sicurezza 22

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