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Cisco Security Appliance Command Line Configuration Guide
OL-10088-01
Chapter 25 Configuring Application Layer Protocol Inspection
SNMP Inspection
An SMTP server responds to client requests with numeric reply codes and optional human-readable
strings. SMTP application inspection controls and reduces the commands that the user can use as well
as the messages that the server returns. SMTP inspection performs three primary tasks:
• Restricts SMTP requests to seven basic SMTP commands and eight extended commands.
• Monitors the SMTP command-response sequence.
• Generates an audit trail—Audit record 108002 is generated when invalid character embedded in the
mail address is replaced. For more information, see RFC 821.
SMTP inspection monitors the command and response sequence for the following anomalous signatures:
• Truncated commands.
• Incorrect command termination (not terminated with <CR><LR>).
• The MAIL and RCPT commands specify who are the sender and the receiver of the mail. Mail
addresses are scanned for strange characters. The pipeline character (|) is deleted (changed to a blank
space) and “<” ‚”>” are only allowed if they are used to define a mail address (“>” must be preceded
by “<”).
• Unexpected transition by the SMTP server.
• For unknown commands, the security appliance changes all the characters in the packet to X. In this
case, the server generates an error code to the client. Because of the change in the packed, the TCP
checksum has to be recalculated or adjusted.
• TCP stream editing.
• Command pipelining.
SNMP Inspection
SNMP application inspection lets you restrict SNMP traffic to a specific version of SNMP. Earlier
versions of SNMP are less secure; therefore, denying certain SNMP versions may be required by your
security policy. The security appliance can deny SNMP versions 1, 2, 2c, or 3. You control the versions
permitted by creating an SNMP map. You then apply the SNMP map when you enable SNMP inspection
according to the “Configuring Application Inspection” section on page 25-5.
To create an SNMP inspection policy map, perform the following steps:
Step 1 To create an SNMP map, enter the following command:
hostname(config)# snmp-map map_name
hostname(config-snmp-map)#
where map_name is the name of the SNMP map. The CLI enters SNMP map configuration mode.
Step 2 To specify the versions of SNMP to deny, enter the following command for each version:
hostname(config-snmp-map)# deny version version
hostname(config-snmp-map)#
where version is 1, 2, 2c, or 3.
The following example denies SNMP Versions 1 and 2:
hostname(config)# snmp-map sample_map
hostname(config-snmp-map)# deny version 1
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