Network internet internet internal ip addresses

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network Internet Internet Internal IP Addresses 219.22.165.1 Corporate LAN 192.172.1.1-192.172.1.254 Public IP Address(es)
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Receive packet NAT Search session table Check Filtering rules Add state entry QoS Classification & Marking Routing Transmit packet Check session state Following packets First packet Allo w Casual stateful packet filtering processing 25 Session table
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Application Level gateway firewalls  also called proxy firewall Whereas a packet filter is capable of inspecting data only in the lower levels of an IP packet, such as the IP address or port number, an application proxy is capable of inspecting the entire application data portion of an IP packet. The internal network computer sends a particular Internet request to the firewall. The application proxy on the firewall picks up on the request, inspects the entire packet against rules configured by the firewall administrator, and then regenerates the entire Internet request before sending it to the destination server on the Internet. The firewall appears to have sent the request. The returned result will again be inspected, and if the rules allow the result to pass, the firewall will build a response packet and send it to the internal network computer .
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Application Gateway or Proxy Applications Presentations Sessions Transport Data Link Physical Data Link Physical Applications Presentations Sessions Transport Data Link Physical Network Network Network Presentations Sessions Transport Applications Packets examined at the application layer Application/Content filtering possible - prevent  FTP  put  commands, for example Modest performance Scalability limited
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Application Level gateway firewalls  called proxy firewall  Advantages : The application proxy can inspect the entire application portion of the IP packet. This inspection happens both when the Internet request is sent and when the reply packet from the Internet server is returned. Because the application proxy understands the application protocol, it can create a much more detailed log file of what is sent through the firewall. Packet filter log files know only about the IP packet header information. The internal computer and the server on the Internet never have a real connection. Instead, the firewall regenerates every packet that is sent between the two. This means that problems or attacks associated with buffer-overflows or illegal conditions in the packets never reach the internal computer.
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30 Advantages and disadvantages of  proxy gateways Advantages Proxy can log all connections, activity in connections Proxy can provide caching Proxy can do intelligent filtering based on content Proxy can perform user-level authentication Disadvantages Not all services have proxied versions May need different proxy server for each service Requires modification of client Performance
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Introduction 31 Demilitarized Zone (DMZ) Web server FTP server DNS server application gateway Internet Demilitarized zone Internal network firewall
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Thank You! Thank You! Questions? Questions?
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  • Fall '12
  • dr.mahmoudmostafa
  • IP address, Packet filtering

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