cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
569
Views
0
Helpful
4
Replies

Cisco ASA 5510, SMTP Access Issue

NickTuppack
Level 1
Level 1

Hi,

I'm having an issue trying to open port 25 on our cisco ASA 5510 version 9.1 (2). When a wire tap is placed on the outside port between the ASA and the internet we are getting hits on wireshark, when a port 25 trace from http://www.yougetsignal.com/tools/open-ports is run. No hits or activity is showing up on the debug log using ASDM, even when filtering is applied.

Problem is we cannot open port 25 traffic from the outside network to the inside network so that smtp mail can flow to the Exchange server *.102. Mail can go from the inside network to the ouside network and out to the internet no problems (internal being the most trusted obviously).

Please find attatched the config for the ASA. I have replaced the companyname/domain with "ourcompanyname", our public IP to "ourpublicIP", our ISP to OurISP and our internal IP's with *.*.*.* for sanitisation reasons.

Any help would be greatly appreciated.

Cheers

4 Replies 4

Mariusz Bochen
Level 1
Level 1

Hi,

Did you try packet-tracer ?

Regards

Mariusz

DjDamo
Level 1
Level 1

Nick..... there are 3 aspects to this config:

1 Access-l from external to your public IP addr for smtp

2 Access-l from your public IP addr to your internal mail server address

3 NAT rule on the internal mail IP address object.

eg.

access-list outside_access_in extended permit tcp (any or external ip addr object) object external_ip eq smtp
access-list inside_access_in extended permit tcp (any or external ip addr object) object internal_ip eq smtp

object network internal_ip
nat (inside,outside) static external_ip service tcp smtp smtp

 

kevin_giusti
Level 1
Level 1

In the object service for SMTP the source port was defined as 25.  The destination port will be 25 but the source will be a random number from the client.

Try this:

no access-list outside_access_in extended permit object smtp any interface outside 

access-list outside_access_in extended permit tcp any host "SMTP server IP" eq 25

Julio Carvajal
VIP Alumni
VIP Alumni

Hello,

 

So here is what's needed to make this happen and has not been said before

no access-list outside_access_in extended permit object smtp any interface outside 

access-list outside_access_in extended permit tcp any host mail.ourcompany.com_ip_address eq 25

Then

object service smtp
 no service tcp source eq smtp destination eq smtp 

 service tcp source eq 25

 

That's all you need to be able to open and map that port :)

 

Regards,

 

Jcarvaja

 

 

 

Julio Carvajal
Senior Network Security and Core Specialist
CCIE #42930, 2xCCNP, JNCIP-SEC
Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: