Two-interface Router With NAT

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.