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ASA 5520 NAT Problem

I have the following topology: 

 mail server --- swcore --(inside) << >> ASA (outside) --- ISP border router 

  should perform the following nat on the handle of a mail server  to   200.x.x.182 

  I have the following configuration on the ASA: 

object-group service SERVICES 
  service-object tcp-udp eq 7001 
  service-object tcp eq ssh 
  service-object tcp-udp eq 25 
  service-object tcp-udp eq 26 
  service tcp-udp-object eq 993 
  service tcp-udp-object eq 109 
  service tcp-udp-object eq 110 
  service tcp-udp-object eq 143 
  service tcp-udp-object eq 220 
  service tcp-udp-object eq 465 
  service tcp-udp-object eq 468 
  service tcp-udp-object eq 587 
  service tcp-udp-object eq 995 
  service tcp-udp-object eq www 
  service-object tcp-udp eq domain 
  service-object tcp-udp eq 8080 
  service-object tcp-udp eq 8443 
  service-object tcp eq https 
  service tcp-udp-object eq 135 
  service-object tcp eq 135 
  service-object tcp-udp eq 7777 
  service-object tcp-udp eq 8090 
  service-object tcp eq ftp 
  service-object tcp eq ftp-data 
  service-object udp eq ntp 
  service-object tcp eq sqlnet 
  service-object tcp eq 3389 

access-list outside extended permit object-group SERVICES any host 200.x.x.182 
access-list inside extended permit object-group SERVICES host any 
access-group outside in interface outside 
access-group inside in interface inside 

static (inside,outside) tcp 200.x.x.182 smtp smtp netmask

global (outside) 1 interface 
nat (inside) 1 



  Sniffer was performed interface that goes to the core sw to int inside  ASA, and effectively SMTP packets are received from which is the mail server. 

When you execute a "sh nat" does tells you match the .41 port 25 to 200.xx182 

  But when you check the header of the emails sent outside the domain appears the IP address is 200.xx178 with which it is performed the nat for internet company.

  For some reason it is entering the nat 

global (outside) 1 interface 

  And I do not understand because if I can see the sh nat does match the static nat.

border router does not perform any function nat actually execute sh ip nat trans and nothing display.




VIP Mentor

your static NAT only works

The static NAT only works for incoming SMTP, not for outgoing. If you want that all outbound traffic from the mailserver is NATted to .182, you should change your static to the following:

static (inside,outside) 200.x.x.182 netmask

This NAT-statement will work inbound and outbound.

But I can see the "sh nat": 

But I can see the "sh nat": 


match tcp inside host eq 25 outside any
    static translation to 200.x.x.182/25
    translate_hits = 0, untranslate_hits = 26617


But when you check the header of the emails sent outside t appears the IP address is 200.xx178 (nat of internet)

I just need that traffic is NATed smtp mail server because there are other IP addresses server using the same public IP address, so we performed the PAT.


VIP Mentor

> But I can see the "sh nat":

> But I can see the "sh nat": 

You see the translation that is used for incoming SMTP. It is only defined for traffic where TCP/25 is on your side. When you send mail, TCP/25 is used as the destination-port and your local port is a random port-number. That won't match your static.

If you can't translate the IP completely for the mail-server, you can configure an extra dynamic PAT for the server:

nat (inside) 2

global (outside) 2 200.x.x.182

The NAT-ID "2" has to be a free ID in your remaining NAT-config.

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