A role of the transport layer Dian
- The network layer provides a connection point
- The transport layer provides end-connection
Low efficiency reliable connection-oriented TCP
SYN intends to establish a connection with each other
ACK confirmation
FIN intend disconnected from each other
应用:FTP:21 TELNET:23 SSH:22 SMTP:25 HTTPD:80 HTTPDS:443 DNS:53
High efficiency of connectionless unreliable UDP
Application: TFTP: 60 DNS: 53 NTP: 123
Two Dian ACL
acl 2000
rule deny / premit source 192.168.2.1 0.0.0.0 // Create a rule prohibiting the source address (undo delete)
interface G0 / 0/1 // enter the interface
traffic-filter inbount acl 2000 // application interface acl rules
Disable / enable all
rule deny/premit source any
Use advanced ACL, prohibit access 1.1 of 2.1 FTP, prohibit access 2.2 1.1 websites, without limiting other services
acl 3000
rule deny(permit) tcp source 192.168.2.1 0 destination 192.168.1.1 0 destination-port eq 21
rule deny(permit) tcp source 192.168.2.2 0 destination 192.168.1.1 0 destination-port eq 80
interface g0/0/1
traffic-filter inbound(outbount)
