Cisco Systems ASA 5500 manual Determining What Traffic to Scan, 19-9

Chapter 19 Managing the AIP SSM and CSC SSM

Managing the CSC SSM

With a Plus License, the additional features enabled by default are SMTP anti-spam, SMTP content filtering, POP3 anti-spam, URL blocking, and URL filtering.

To access the CSC SSM GUI, in ASDM choose Configuration > Trend Micro Content Security, and then select one of the following: Web, Mail, File Transfer, or Updates. The blue links on these panes, beginning with the word “Configure”, open the CSC SSM GUI.

Determining What Traffic to Scan

The CSC SSM can scan FTP, HTTP, POP3, and SMTP traffic. It supports these protocols only when the destination port of the packet requesting the connection is the well known port for the protocol, that is, CSC SSM can scan only the following connections:

•FTP connections opened to TCP port 21.

•HTTP connections opened to TCP port 80.

•POP3 connections opened to TCP port 110.

•SMTP connections opened to TCP port 25.

You can choose to scan traffic for all of these protocols or any combination of them. For example, if you do not allow network users to receive POP3 email, you would not want to configure the adaptive security appliance to divert POP3 traffic to the CSC SSM (you would want to block it instead).

To maximize performance of the adaptive security appliance and the CSC SSM, divert to the CSC SSM only the traffic that you want the CSC SSM to scan. Needlessly diverting traffic that you do not want to scan, such as traffic between a trusted source and destination, can adversely affect network performance.

The action of scanning traffic with the CSC SSM is enabled with the csc command, which must be part of a service policy. Service policies can be applied globally or to specific interfaces; therefore, you can choose to enable the csc command globally or for specific interfaces.

Adding the csc command to your global policy ensures that all unencrypted connections through the adaptive security appliance are scanned by the CSC SSM; however, this may mean that traffic from trusted sources is needlessly scanned.

If you enable the csc command in interface-specific service policies, it is bi-directional. This means that when the adaptive security appliance opens a new connection, if the csc command is active on either the inbound or the outbound interface of the connection and if the class map for the policy identifies traffic for scanning, the adaptive security appliance diverts it to the CSC SSM.

However, bi-directionality means that if you divert to the CSC SSM any of the supported traffic types that cross a given interface, the CSC SSM is likely performing needless scans on traffic from your trusted inside networks. For example, URLs and files requested from web servers on a DMZ network are unlikely to pose content security risks to hosts on an inside network and you probably do not want the adaptive security appliance to divert such traffic to the CSC SSM.

Therefore, we highly recommend using access lists to further limit the traffic selected by the class maps of CSC SSM service policies. Specifically, use access lists that match the following:

•HTTP connections to outside networks.

•FTP connections from clients inside the adaptive security appliance to servers outside the adaptive security appliance.

•POP3 connections from clients inside the security appliance to servers outside the adaptive security appliance.

Cisco Security Appliance Command Line Configuration Guide

OL-8629-01 19-9