G.shdsl Router User Manual 152
50
Click Advanced Firewall Security and
then press Finish.
A SYN flood attack attempts to slow
your network by requesting new
connections but not completing the
process to open the connection.
Once the buffer for these pending
connections is full a server will not
accept any more connections and
will be unresponsive.
ICMP Flood: A sender transmits a
volume of ICMP request packets to
cause all CPU resources to be
consumed serving the phony requests.
UDP Flood: A sender transmits a volume of requests for UDP diagnostic services which cause all
CPU resources to be consumed serving the phony requests.
A ping of death attack attempts to crash your system by sending a fragmented packet, when
reconstructed is larger than the maximum allowable size. Other known variants of the ping of death
include teardrop, bonk and nestea.
A land attack is an attempt to slow your network down by sending a packet with identical source
and destination addresses originating from your network.
IP Spoofing is a method of masking the identity of an intrusion by making it appeared that the traffic
came from a different computer. This is used by intruders to keep their anonymity and can be used
in a Denial of Service attack.
A smurf attack involves two systems. The attacker sends a packet containing a ICMP echo request
(ping) to the network address of one system. This system is known as the amplifier. The return
address of the ping has been faked (spoofed) to appear to come from a machine on another
network (the victim). The victim is then flooded with responses to the ping. As many responses are
generated for only one attack, the attacker is able use many amplifiers on the same victim.
IP Spoofing: Falsify the IP header information to deceive the destination host.
Traditional firewall are stateless meaning they have no memory of the connections of data or
packets that pass through them. Such IP filtering firewalls simply examine header information in
each packet and attempt to match it to a set of define rule. If the firewall finds a match, the
prescribe action is taken. If no match is found, the packet is accepted into the network, or dropped,
depending on the firewall configuration.
A stateful firewall maintains a memory of each connection and data passing through it. Stateful
firewall records the context of connections during each session, continuously updating state
information in dynamic tables. With this information, stateful firewalls inspect each connection
traversing each interface of the firewall, testing the validity of data packets throughout each
session. As data arrives, it is checked against the state tables and if the data is part of the session,
it is accepted. Stateful firewalls enable a more intelligent, flexible and robust approach to network
security, while defeating most intrusion methods that exploit state-less IP filtering firewalls.
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