cisco certification beginners

cisco certification beginners.Stateful inspection firewalls. Next-generation context-aware firewalls.Packet filtering techniques.The use of packet filters is limited to access control for certain specified network segments, implemented by defining which traffic can pass through which segments. Packet filters are typically deployed to inspect incoming traffic at the transport layer of the Open Systems Interconnection (OSI) model. Let's say a packet filter can analyze a Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) packet and compare something in the packet with a predefined set of rules called an Access Control List [ACL].A packet filter can examine the following elements in a packet.The source IP address.The destination IP address. The source port number. Destination port number. Protocol type.In general, ACLs can be configured both on firewalls and on network infrastructure devices (for example, devices such as route brick pointers, switches, and wireless access controllers [WLCs]). Each ACL is referred to as an access control record (ACE).The ACE passes through the Layer 2 . The ACE classifies packets by examining certain information in the Layer 4 protocol header. The information that the ACE examines includes the following. Layer 2 protocol information, for example, Ethernet type.Layer 3 protocol information, for example, ICMP, TCP, or UDPOLayer 3 header information, for example, source and destination IP addresses.Layer 4 header information, for example, source and destination TCP or UDP port numbers. Once an ACL is properly configured, it can be applied to an interface to filter traffic to and from that interface. Packets can be filtered in both the inbound and outbound directions of a firewall or network device interface. When an ACL is applied in the inbound direction of an interface, the security device receives the packet and compares the ACE contained in the ACL with certain information in the packet. If the ACL allows the packet to pass, the security device continues to process the packet and eventually sends it outbound from the outbound interface. The main difference between a router ACL and a CiscoASA (stateful firewall) ACL is that the CiscoASA will only let the ACL detect the first packet of a data stream. After that a connection will be established and subsequent packets matching this connection will no longer be detected by the ACL. If the ACL tells the CiscoASA to reject the packet, the CiscoASA does a packet drop and also generates a Syslog message indicating that such a packet drop event has occurred.