cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
724
Views
0
Helpful
3
Replies

Prevent spam before router

elelvis19
Level 1
Level 1

Hi,

We are a small ISP and we have a problem in one of our locations, we have a Router 2811 with 5Mb of internet and around 50 clients behind, the router in the WAN interface have a public IP and is doing NAT to the LAN interface of clients and the problem is that one or more clients PCs are sending spam to the internet and that's why the public IP of the WAN interface is too often in some DNSBLs or blacklist and some other clients when they send emails from they own domains doesn't arrive because it's say that the IP of the WAN interface is in a blacklist.

The question is, can we do something to prevent this without have to change the public IP????

3 Replies 3

Danilo Dy
VIP Alumni
VIP Alumni

With existing device/resources, the answer is no. Even if you keep changing the IP Address, the user will keep sending SPAM mail (intentional/unintentional).

You should take a look at Cisco IronPort http://www.ironport.com/

its possible to stop the spam mails by applying access-list which will allow the smtp port for only their mail server and deny the remaining.

where is your mail server located.

I agree. I'd block all outbound smtp except from specifically permitted IP addresses. Of course this means you'll need static addressing on the NAT side and need to apply the ACL to the "inside" interface.

-Chris

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: