Installing and Administering PPP

124 Chapter 5
Security Techniques
Closed Policy Filter Example
8/icmp/192.168.199.11 # permit ping of DNS server
8/icmp/192.168.199.12 # permit ping of FTP server
8/icmp/192.168.199.13 # permit ping of WWW server
8/icmp/192.168.199.14 # permit ping of SMTP server
!8/icmp/recv # block inbound ping address scanning
icmp # permit ICMP messages
!all # block all other packets
keepup
!send # outbound traffic
!3/icmp # ICMP unreachable messages
!5/icmp # ICMP redirect messages
!11/icmp # ICMP time exceeded messages
!who # WHO protocol
!route # routed/gated RIP protocol
!ntp # Network Time Protocol
all # permit all other packets
log
!8/icmp # ICMP ECHO packets
rejected # packets rejected by packet filter
tcp/syn # all TCP connection requests
!all # block all other packets