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Firewalls Firewalls
Marin Stamov
IntroductionIntroductionTechnological barrier designed to
prevent unauthorized or unwanted communications between computer networks or hosts
Invented in the early 1990sFirst line of defenseProtect against hackers and worms
Firewall typesFirewall typesPacket filter (stateless)Packet filter (stateful)Hardware firewallNAT firewallProxy firewallTransparent firewallPersonal firewall
Packet filtersPacket filters
Packet filter (stateful)Packet filter (stateful)When a packet reaches the
firewall, it is run against a set of rules.
The rules determine an action to take for the packet
Accept – Let the traffic pass throughReject – Block the packet and return an ICMP
“Communication administratively prohibited”Drop – Block the packet Packets with the SYN bit set are considered by
the firewall as new connections
Firewall rulesFirewall rules
Hardware firewallHardware firewallCiscoPIX
NAT firewall, NAT firewall, AKA "Masquerading"AKA "Masquerading"NAT stands for Network Address
TranslationOriginally developed to address the
limited number of IPv4 routable addresses
Hides the true address of protected hosts
Requires no special configuration on the client side. Clients just have to know their default gateway.
NATNAT
Proxy firewallProxy firewallRuns software that allows
specific programs to functionCan provide anonymityAllowing only specific protocols
that you wish to supportAware of the data format it
handles, and can look for many things inside the data.
Proxy firewallProxy firewallSquid - a proxy server and web
cache daemon.
Transparent firewallTransparent firewall
Personal firewallPersonal firewallProtect only the computer on
which it is installed.May prompt the user each time a
connection is attempted and adapt security policy accordingly.
May provide some level of intrusion detection
FirewallsFirewalls
ConclusionConclusionEach type of firewall does
different things, and can be more or less useful depending on the current scenario
Open only ports that you need
Always test your firewall from the outside
Questions?Questions?