Document ID: 113336
Updated: Nov 30, 2011
Contents
Introduction
This sample configuration demonstrates 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 the DMZ Configuration Example for more information on how to set up the ASA Security Appliance for access to a mail/SMTP server located on the DMZ network.
Refer to ASA 8.3 and Later: Mail (SMTP) Server Access on Outside Network Configuration Exampleto 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 later: Mail (SMTP) Server Access on Inside Network Configuration Example for more information of the identical configuration on Cisco Adaptive Security Appliance (ASA) with versions 8.2 and earlier.
Prerequisites
Requirements
There are no specific requirements for this document.
Components Used
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.
Conventions
Refer to the Cisco Technical Tips Conventions for more information on document conventions.
Configure
In this section, you are presented with the information to configure the features described in this document.
Note: Use the Command Lookup Tool (registered customers only) to obtain more information on the commands used in this section.
Network Diagram
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 (192.168.1.0/24) and the outside network (209.164.3.0/30). The mail server with IP address 209.64.3.5 is located in the inside network.
Configurations
This document uses these configurations:
| ASA |
|---|
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 no security-level no ip address ! interface Ethernet1 shutdown no nameif no security-level no ip address ! interface Ethernet2 shutdown no nameif no security-level no ip address ! !--- Define the IP address for the inside interface. interface Ethernet3 nameif inside security-level 100 ip address 192.168.1.1 255.255.255.0 ! !--- Define the IP address for the outside interface. interface Ethernet4 nameif outside security-level 0 ip address 209.164.3.1 255.255.255.252 ! interface Ethernet5 shutdown no nameif no security-level no ip address ! passwd 2KFQnbNIdI.2KYOU encrypted ftp mode passive !--- Create an access list that permits Simple !--- Mail Transfer Protocol (SMTP) traffic from anywhere !--- to the host at 209.164.3.5 (our server). The name of this list is !--- smtp. Add additional lines to this access list as required. !--- Note: There is one and only one access list allowed per !--- interface per direction, for example, inbound on the outside interface. !--- Because of limitation, any additional lines that need placement in !--- the access list need to be specified here. If the server !--- in question is not SMTP, replace the occurrences of SMTP with !--- www, DNS, POP3, or whatever else is required. access-list smtp extended permit tcp any host 209.164.3.5 eq smtp pager lines 24 mtu inside 1500 mtu outside 1500 no failover no asdm history enable arp timeout 14400 !--- Specify that any traffic that originates inside from the !--- 192.168.2.x network NATs (PAT) to 209.164.3.129 if !--- such traffic passes through the outside interface. object network obj-192.168.2.0 subnet 192.168.2.0 255.255.255.0 nat (inside,outside) dynamic 209.164.3.129 !--- Define a static translation between 192.168.2.57 on the inside and !--- 209.164.3.5 on the outside. These are the addresses to be used by !--- the server located inside the ASA. object network obj-192.168.2.57 host 192.168.2.57 nat (inside,outside) static 209.164.3.5 !--- Apply the access list named smtp inbound on the outside interface. access-group smtp in interface outside !--- Instruct the ASA to hand any traffic destined for 192.168.x.x !--- to the router at 192.168.1.2. route inside 192.168.0.0 255.255.0.0 192.168.1.2 1 !--- Set the default route to 209.164.3.2. !--- The ASA assumes that this address is a router address. route outside 0.0.0.0 0.0.0.0 209.164.3.2 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 snmp-server enable traps snmp authentication linkup linkdown coldstart telnet timeout 5 ssh timeout 5 console timeout 0 ! class-map inspection_default match default-inspection-traffic ! ! !--- SMTP/ESMTP is inspected as "inspect esmtp" is included in the map. 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 ! !--- SMTP/ESMTP is inspected as "inspect esmtp" is included in the map. service-policy global_policy global Cryptochecksum:f96eaf0268573bd1af005e1db9391284 : end |
| Router B |
|---|
Current configuration: ! version 12.4 service timestamps debug uptime service timestamps log uptime no service password-encryption ! hostname 2522-R5 ! enable secret 5 $1$N0F3$XE2aJhJlCbLWYloDwNvcV. ! ip subnet-zero ! ! ! ! ! interface Ethernet0 !--- Sets the IP address of the Ethernet interface to 209.164.3.2. ip address 209.164.3.2 255.255.255.252 ! interface Serial0 !--- Instructs the serial interface to use !--- the address of the Ethernet interface when the need arises. ip unnumbered ethernet 0 ! interface Serial1 no ip address no ip directed-broadcast ! ip classless !--- Instructs the router to send all traffic !--- destined for 209.164.3.x to 209.164.3.1. ip route 209.164.3.0 255.255.255.0 209.164.3.1 !--- Instructs the router to send !--- all other remote traffic out serial 0. ip route 0.0.0.0 0.0.0.0 serial 0 ! ! line con 0 transport input none line aux 0 autoselect during-login line vty 0 4 exec-timeout 5 0 password ww login ! end |
Note: The Router A configuration is not added. You only have to give the IP addresses on the interfaces and set the default gateway to 192.168.1.1, which is the inside interface of the ASA .
ESMTP TLS Configuration
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
Note: In ASA version 8.0.3 and later, the allow-tls command is available to allow TLS email with inspect esmtp enabled as shown:
policy-map type inspect esmtp tls-esmtp parameters allow-tls inspect esmtp tls-esmtp
Verify
There is currently no verification procedure available for this configuration.
Troubleshoot
The Output Interpreter Tool (registered customers only) (OIT) supports certain show commands. Use the OIT to view an analysis of show command output.
The logging buffered 7 command directs messages to the ASA console. If connectivity to the mail server is a problem, examine the console debug messages to locate the IP addresses of the sending and receiving stations in order to determine the problem.
Related Information
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Refer to Cisco Technical Tips Conventions for information on conventions used in this document.