cisco ccna 200-301 online course

cisco ccna 200-301 online course.The established keyword is used only for TCP connections. This keyword is used in cases where TCP traffic is sent outbound from inside the networkand the returned traffic is to be filtered. In this case, this keyword allows such TCP traffic to pass, i.e., TCP data segment headers with a specific flag bit indicating that they are returned. For connection-oriented transport protocols, see Chapter 2; for TCP mechanisms, see Chapter 8. The author's book Cisco Router Fireball Security (CiscoPress, 2004) discusses this topic in much greater depth, with a review of keywords.The author's book, Cisco Router Fireball Security (CiscoPress, 2004), discusses this topic in much greater depth, comparing how the keyword established and stateful firewalls work.Exam points Make sure you understand the use of the keyword established in TCPACL statements. ...-guy-established...Video 21.03 A multimedia demonstration of configuring an extended numbered ACL to allow Telnet traffic to pass through a router is included in the companion digital resource to this book.ICMP The following commands demonstrate the syntax for filtering ICMP traffic.Router(config)# access-list 100-199|2000-2699 (permit | deny} icmp source_address source_wildcard_mask destination_address destination_ wildcard_mask [icmp_message] [log]Unlike TCP and UDP, ICMP does not filter by port, but by message type. TCP and UDP extended ACLs let you specify the source and destination ports, while ICMP extended ACLs let you specify the ICMP message type. Table 21.8 lists some common ICMP message types and provides a brief description. To specify an ICMP message type, enter a name or number. If you do not specify an ICMP message type, it will match all ICMP message types.To delete an ACL and its statements, use the command no access-Ust,and specify the number of that ACL. You can also add the parameter no before the numbered ACL statement, which has the same effect as the command no access-list: the entire ACL will be deleted, but most administrators do not recognize or forget this. For example, if you execute the command no access-list 100 permit tcp any any,the router will ignore everything after the parameter 100, just as if you had executed the command no access-list 100.The companion digital resource to this book contains the configuration of extended numbered ACLs to allow ICMP traffic through the router