ccna 300-201 practice test

ccna 300-201 practice test.Packet filters are vulnerable to IP spoofing. Hackers can send arbitrary packets that match ACL rules and get past the filter.Packet filters do not filter sliced packets because sliced IP packets contain a TCP header in the first slice. and packet filters perform filtering based on information in the TCP header. after the first slice passes. all subsequent slices will pass unconditionally. When using packet filters, assume that the filter for the first slice accurately enforces the filtering policy. Complex ACLs are difficult to implement and maintain accurately. Packet filters cannot dynamically filter certain services. For example, if access to an entire range of ports is not open, it is difficult to filter the packets that makeSessions negotiated with dynamic ports. The packet filter is stateless. It examines each packet one by one, rather than examining the state context of the connection. Packet filters are not a complete firewall solution, but they are an important component.4.2.2.3 Stateful FirewallsStateful firewalls are the most general and common firewall technology. Stateful firewalls provide stateful packet filtering using connection information stored in a stateful table. For some applications, although stateful filtering can analyze OSI model Layer 4 and Layer 5 traffic, it is part of the network layer in the firewall architecture.Unlike static packet filtering, which examines only the information in the packet headers, stateful filtering tracks every . each connection to confirm that the connection is valid. Stateful firewalls use a status table to track the actual communication process. The firewall examines the header information in Layer 3 data packets and Layer 4 data segments. For example, the firewall looks at the synchronization (SYN), reset (RST), acknowledgement (ACK), end (FIN), and other control codes in the TCP header to determine the status of the connection.When accessing an external service, the stateful packet filtering firewall stores the request status in a status table, thereby maintaining certain details about the request. Each time an inbound or outbound connection to a TCP or UDP connection is established, the firewall records information in the stateful session flow table. After the external system responds to the request, the firewall server compares the received packet with the stored state and determines whether to allow or deny network access OThe stateful session flow table contains source and destination addresses, port numbers, TCP sequence information, and additional flags for TCP or UDP connections associated with a particular session. This information creates a connection object that is used by Firewise to compare all inbound and outbound packets to the session flows in the Stateful Session Flow table. The firewall runs that data through only if an appropriate connection exists to verify the passage of that data.Note: This was also the behavior of previous versions of the 10S firewall that implemented stateful filtering. newer versions of the CiscoIOS firewall use a zone-based approach that operates as a function of the interface (rather than a complex access control list). Higher-level stateful firewalls include the ability to parse FTP port commands and update the state table to allow FTP to pass through the firewall transparently. Advanced stateful firewalls can also provide interpretation of TCP sequence numbers and DNS lookup and response matching to ensure that the number of firewall allowed