Basic concept of Firewall & ACL

We must know Basic concept of Firewall ; 

• Inbound on the internal interface
• Outbound on the external interface
• Inbound on the external interface
• Outbound on the internal interface
• Source & Distination 

Configure a Router as a Firewall

Access-list 101 deny ip any any


-> Allow incoming traffic to a HTTP/HTTPS server located at 192.1.12.11
Access-list 101 permit tcp any host 192.1.12.11 eq 80

-> Allow incoming traffic to a SMTP server located at 192.1.12.12.
Access-list 101 permit tcp any host 192.1.12.12 eq 25

->Allow incoming traffic to a Telnet server located at 192.1.12.13.
Access-list 101 permit tcp any host 192.1.12.13 eq 23

->Allow R3 to Telnet and SSH to R1.
Access-list 101 permit tcp host 192.1.23.3 host 192.1.12.1 eq 23

->Routing Traffic from R3
Access-list 101 permit eigrp host 192.1.23.3 any
!