This sample configuration demonstrates how to set up the ASA Security Appliance for access to a Simple Mail Transfer Protocol (SMTP) server located on the Demilitarized Zone (DMZ) network.
Refer to ASA 8.3 and Later: Mail (SMTP) Server Access on Inside Network Configuration Example for more information on how to set up the ASA Security Appliance for access to a mail/SMTP server located on the Inside network.
Refer to ASA 8.3 and Later: Mail (SMTP) Server Access on Outside Network Configuration Example for more information on how to set up the ASA Security Appliance for access to a mail/SMTP server located on the Outside network.
Refer to PIX/ASA 7.x and above: Mail (SMTP) Server Access on the DMZ Configuration Example for identical configuration on Cisco Adaptive Security Appliance (ASA) with versions 8.2 and earlier.
There are no specific requirements for this document.
The information in this document is based on these software and hardware versions:
Cisco Adaptive Security Appliance (ASA) that runs version 8.3 and later.
Cisco 1841 Router with Cisco IOS® Software Release 12.4(20)T
The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.
Refer to the Cisco Technical Tips Conventions for more information on document conventions.
In this section, you are presented with the information to configure the features described in this document.
This document uses this network setup:
Note: The IP addressing schemes used in this configuration are not legally routable on the Internet. They are RFC 1918 addresses that have been used in a lab environment.
The network setup used in this example has the ASA with inside network (10.1.1.0/24) and the outside network (192.168.200.0/27). The mail server with IP address 172.16.31.10 is located in the Demilitarized Zone (DMZ) network. For the Mailserver to be accessed by the inside, users configure the identity NAT. Configure an access list, which is dmz_int in this example, in order to allow the outgoing SMTP connections from the Mailserver to the hosts in the inside network and bind it to the DMZ interface.
Similarly for the outside users to access the Mailserver configure a static NAT and also an access list, which is outside_int in this example, in order to permit outside users to access the Mailserver and bind this access list to the outside interface.
This document uses this configuration:
ASA#show run : Saved : ASA Version 8.3(1) ! hostname ASA enable password 8Ry2YjIyt7RRXU24 encrypted passwd 2KFQnbNIdI.2KYOU encrypted names ! interface Ethernet0 shutdown no nameif security-level 0 no ip address ! interface Ethernet1 shutdown no nameif no security-level no ip address ! interface Ethernet2 no nameif no security-level no ip address ! !--- Configure the inside interface. interface Ethernet3 nameif inside security-level 100 ip address 10.1.1.1 255.255.255.0 ! !--- Configure the outside interface. interface Ethernet4 nameif outside security-level 0 ip address 192.168.200.225 255.255.255.224 ! !--- Configure dmz interface. interface Ethernet5 nameif dmz security-level 10 ip address 172.16.31.1 255.255.255.0 ! passwd 2KFQnbNIdI.2KYOU encrypted boot system disk0:/asa831-k8.bin ftp mode passive !--- This access list allows hosts to access !--- IP address 192.168.200.227 for the SMTP port. access-list outside_int extended permit tcp any host 192.168.200.227 eq smtp !--- Allows outgoing SMTP connections. !--- This access list allows host IP 172.16.31.10 !--- sourcing the SMTP port to access any host. access-list dmz_int extended permit tcp host 172.16.31.10 eq smtp any pager lines 24 mtu BB 1500 mtu inside 1500 mtu outside 1500 mtu dmz 1500 no failover no asdm history enable arp timeout 14400 object network obj-192.168.200.228-192.168.200.253 range 192.168.200.228-192.168.200.253 object network obj-192.168.200.254 host 192.168.200.254 object-group network nat-pat-group network-object object obj-192.168.200.228-192.168.200.253 network-object object obj-192.168.200.254 object network obj-10.1.1.0 subnet 10.1.1.0 255.255.255.0 nat (inside,outside) dynamic nat-pat-group !--- This network static does not use address translation. !--- Inside hosts appear on the DMZ with their own addresses. object network obj-10.1.1.0 subnet 10.1.1.0 255.255.255.0 nat (inside,dmz) static obj-10.1.1.0 !--- This network static uses address translation. !--- Hosts that access the mail server from the outside !--- use the 192.168.200.227 address. object network obj-172.16.31.10 host 172.16.31.10 nat (dmz,outside) static 192.168.200.227 access-group outside_int in interface outside access-group dmz_int in interface dmz route outside 0.0.0.0 0.0.0.0 192.168.200.226 1 timeout xlate 3:00:00 timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 icmp 0:00:02 timeout sunrpc 0:10:00 h323 0:05:00 h225 1:00:00 mgcp 0:05:00 timeout mgcp-pat 0:05:00 sip 0:30:00 sip_media 0:02:00 timeout uauth 0:05:00 absolute no snmp-server location no snmp-server contact telnet timeout 5 ssh timeout 5 console timeout 0 ! class-map inspection_default match default-inspection-traffic ! ! !--- The inspect esmtp command (included in the map) allows !--- SMTP/ESMTP to inspect the application. policy-map global_policy class inspection_default inspect dns maximum-length 512 inspect ftp inspect h323 h225 inspect h323 ras inspect netbios inspect rsh inspect rtsp inspect skinny inspect esmtp inspect sqlnet inspect sunrpc inspect tftp inspect sip inspect xdmcp ! !--- The inspect esmtp command (included in the map) allows !--- SMTP/ESMTP to inspect the application. service-policy global_policy global Cryptochecksum:2653ce2c9446fb244b410c2161a63eda : end [OK]
Note: If you use Transport Layer Security (TLS) encryption for e-mail communication then the ESMTP inspection feature (enabled by default) in the ASA drops the packets. In order to allow the e-mails with TLS enabled, disable the ESMTP inspection feature as this output shows. Refer to Cisco bug ID CSCtn08326 (registered customers only) for more information.
ciscoasa(config)# policy-map global_policy ciscoasa(config-pmap)#class inspection_default ciscoasa(config-pmap-c)#no inspect esmtp ciscoasa(config-pmap-c)#exit ciscoasa(config-pmap)#exit
There is currently no verification procedure available for this configuration.
This section provides information you can use to troubleshoot your configuration.
debug icmp trace —Shows whether Internet Control Message Protocol (ICMP) requests from the hosts reach the ASA. You need to add the access-list command in order to permit ICMP in your configuration in order to run this debug.
Note: In order to use this debug, make sure you allow ICMP in the access-list outside_int as this output shows:
access-list outside_int extended permit tcp any host 192.168.200.227 eq smtp access-list outside_int extended permit icmp any any
logging buffered 7 —Used in global configuration mode to enable the adaptive security appliance to send syslog messages to the log buffer. The contents of the ASA log buffer can be seen with the show logging command.
Refer to Configure Syslog using ASDM for more information on how to set up logging.
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Refer to Cisco Technical Tips Conventions for information on conventions used in this document.