Cisco Systems and the ASA Services Module Manual De Usuario

This chapter describes how to configure application layer protocol inspection. Inspection engines are 
required for services that embed IP addressing information in the user data packet or that open secondary 
channels on dynamically assigned ports. These protocols require the ASA to do a deep packet inspection 
instead of passing the packet through the fast path. As a result, inspection engines can affect overall 
throughput.

Several common inspection engines are enabled on the ASA by default, but you might need to enable 
others depending on your network. 

This chapter includes the following sections:

The ILS inspection engine provides NAT support for Microsoft NetMeeting, SiteServer, and Active 
Directory products that use LDAP to exchange directory information with an ILS server.

The ASA supports NAT for ILS, which is used to register and locate endpoints in the ILS or SiteServer 
Directory. PAT cannot be supported because only IP addresses are stored by an LDAP database. 

For search responses, when the LDAP server is located outside, NAT should be considered to allow 
internal peers to communicate locally while registered to external LDAP servers. For such search 
responses, xlates are searched first, and then DNAT entries to obtain the correct address. If both of these 
searches fail, then the address is not changed. For sites using NAT 0 (no NAT) and not expecting DNAT 
interaction, we recommend that the inspection engine be turned off to provide better performance.

Additional configuration may be necessary when the ILS server is located inside the ASA border. This 
would require a hole for outside clients to access the LDAP server on the specified port, typically TCP 
389. 

Because ILS traffic only occurs on the secondary UDP channel, the TCP connection is disconnected after 
the TCP inactivity interval. By default, this interval is 60 minutes and can be adjusted using the timeout 
command.

ILS/LDAP follows a client/server model with sessions handled over a single TCP connection. 
Depending on the client's actions, several of these sessions may be created.