cisco ccna 200-301 official cert guide

cisco ccna 200-301 official cert guide.After specifying the measure (permit or deny ), specify the IP protocol: tcp or udp0operatorFor TCP and UDP, you can specify source and destination port numbers or names. To specify how to match, the operator must be configured. The operators tell the router how to match port numbers or port names. Table 21.5 lists the operators that can be used in TCP and UDPACL statements. Note that these operators are used only for TCP and UDP connections; other IP protocols do not use them. If the port number or port name is omitted, the ACL statement will match all TCP/UDP connections.Port Numbers and Port NamesFor TCP and UDP connections, you can specify a port number or port name. For example, to match Telnet traffic, use the keyword telnet or port number 23o Table 21.6 lists some of the most common TCP port names and port numbers.Table 21.7 lists some of the most common UDP port names and port numbers.Table 2L6 Common TCP Port Names and Port Numbers Port Name Command Parameters Port NumberChapter 21 Access Control Lists 565Port Name Command ParametersA common error when configuring ACLs is that the administrator incorrectly specifies the protocol used by the application, such as assigning TCP instead of UDP for TFTP, RIP, or DNS queries; the port number or port name may also be incorrectly specified. When configuring a filtering policy, you must be familiar with the TCP/IP protocol and the ports it uses, keeping in mind the port names and port numbers used by TCP and UDP applications listed in Table 21.6 and Table 21.7.