2514 Router Current configuration: ! version 12.0 service timestamps debug uptime service timestamps log uptime no service passWord-encryption ! hostname horton ! enable secret 5 $1$GwRz$YS/82LXSYcgD1d5Nua9Ob1 enable password ww ! ip subnet-zero ! ip inspect name ethernetin cuseeme timeout 3600 ip inspect name ethernetin FTP timeout 3600 ip inspect name ethernetin h323 timeout 3600 ip inspect name ethernetin http timeout 3600 ip inspect name ethernetin rcmd timeout 3600 ip inspect name ethernetin realaudio timeout 3600 ip inspect name ethernetin smtp timeout 3600 ip inspect name ethernetin sqlnet timeout 3600 ip inspect name ethernetin streamworks timeout 3600 ip inspect name ethernetin tcp timeout 3600 ip inspect name ethernetin tftp timeout 30 ip inspect name ethernetin udp timeout 15 ip inspect name ethernetin vdolive timeout 3600
! interface Ethernet0 ip address 20.20.20.2 255.255.255.0 ip access-group 101 in no ip directed-broadcast ip nat inside ip inspect ethernetin in ! interface Ethernet1 no ip address no ip directed-broadcast shutdown ! interface Serial0 ip address 150.150.150.1 255.255.255.0 ip access-group 112 in no ip directed-broadcast ip nat outside clockrate 4000000 ! interface Serial1 no ip address no ip directed-broadcast shutdown ! ip nat pool serialzero 150.150.150.3 150.150.150.255 netmask 255.255.255.0 ip nat inside source list 1 pool serialzero ip classless ip route 0.0.0.0 0.0.0.0 150.150.150.2 ip route 20.30.30.0 255.255.255.0 20.20.20.1 ! access-list 1 permit 20.0.0.0 0.255.255.255 access-list 101 permit tcp 20.0.0.0 0.255.255.255 any access-list 101 permit udp 20.0.0.0 0.255.255.255 any access-list 101 permit icmp 20.0.0.0 0.255.255.255 any access-list 112 permit icmp any 150.150.150.0 0.0.0.255 unreachable access-list 112 permit icmp any 150.150.150.0 0.0.0.255 echo-reply access-list 112 permit icmp any 150.150.150.0 0.0.0.255 packet-too-big access-list 112 permit icmp any 150.150.150.0 0.0.0.255 time-exceeded access-list 112 permit icmp any 150.150.150.0 0.0.0.255 traceroute access-list 112 permit icmp any 150.150.150.0 0.0.0.255 administratively-PRohibited access-list 112 permit icmp any 150.150.150.0 0.0.0.255 echo access-list 112 permit tcp host 150.150.150.2 host 150.150.150.1 eq telnet access-list 112 deny ip 127.0.0.0 0.255.255.255 any access-list 112 deny ip any any ! line con 0 transport input none line aux 0 line vty 0 4 password ww login ! end
关于ip inspect name if you deny SMTP mail on the external ACL, no external SMTP servers will ever be able to make a connection to the internal SMTP server.
CBAC is totally independent of access lists - CBAC is associated with ACLs because one function of CBAC is to ensure return traffic of a session is permitted back to the source - however don't confuse CBAC by thinking ACLs are required. If you apply an inspect list to an interface, inspection takes place, no matter what ACLs are or are not in place. However, remember that ACLs are processed first, so the ACL must allow through the appropriate traffic to be passed thru to the inspection list.
I'm guessing your config would look something like this:
! Internal Interface Interface e0 ip inspect WEB inbound
! External Interface Interface e1 ip access-group 100 in ip inspect SMTP inbound
access-list 100 permit tcp any host x.x.x.x eq smtp access-list 100 deny ip any any
ip inspect name WEB http ip inspect name WEB ftp ip inspect name WEB smtp ip inspect name WEB tcp ip inspect name WEB udp
ip inspect name SMTP smtp
On your external ACL, you must have an opening to allow SMTP in - there is no way CBAC can automatically do this for you as traffic is first processed by the ACL and must pass. So once the SMTP traffic is allowed in, it is passed to the inspection list SMTP, which applys SMTP protocol-based inspection (and opens up any ACLs if necessary - in this example this function is not required).
Note that in this example you could place the SMTP inspection list on the internal interface in the outbound direction as well. This is a better placement option if you had say a DMZ interface that was also receiving SMTP mail for the internal SMTP server, as you would only require a single inspection point (outbound on the internal interface) rather than inbound on the external and DMZ interfaces.
