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Understanding Custom Application Signatures

Application identification supports user-defined custom application signatures to detect applications as they pass through the device. Custom application signatures are unique to your environment and are not part of the predefined application package. You use this custom application signature in SD-WAN policies and firewall policies to steer, and block traffic when a threat is detected.

Custom application signatures are required to:

  • Control traffic particular to an environment.

  • Bring visibility to unknown or unclassified applications.

  • Identify Layer 7 applications or temporary applications, and to achieve further granularity of known applications.

  • Perform QoS for your specific application.

CSO supports the following custom application signatures:

  • ICMP-Based Mapping—The Internet Control Message Protocol (ICMP) mapping technique maps standard ICMP message types and optional codes to a unique application name. This mapping technique lets you differentiate between various types of ICMP messages.

  • IP Address-Based Mapping—Layer 3 and Layer 4 address mapping defines an application by the IP address and optional port range of the traffic.

    To ensure adequate security, use address mapping when the configuration of your private network predicts application traffic to or from trusted servers. Address mapping provides efficiency and accuracy in handling traffic from a known application.

    With Layer 3 and Layer 4 address-based custom applications, you can match the IP address and port range to destination IP address and port range. When IP address and port range are configured, they must match the destination tuples (IP address and port range) of the packet.

    For example, consider a Session Initiation Protocol (SIP) server that initiates sessions from its known port 5060. Because all traffic from this IP address and port is generated by only the SIP application, the SIP application can be mapped to an IP address of the server and port 5060 for application identification. In this way, all traffic with this IP address and port is identified as SIP application traffic.

  • IP Protocol-Based Mapping—Standard IP protocol numbers can map an application to IP traffic. As with address mapping, to ensure adequate security, use IP protocol mapping only in your private network for trusted servers.

  • Layer 7-Based Signatures—Layer 7 custom signatures define an application running over TCP or UDP or Layer 7 applications. Layer 7-based custom application signatures are required for the identification of multiple applications running on the same Layer 7 protocols. For example, applications such as Facebook and Yahoo Messenger can run over HTTP, but there is a need to identify them as two different applications running on the same Layer 7 protocol. The custom signature is cacheable for Layer 7 signatures only. You can create multiple signatures and each signature can contain multiple members (maximum 15 members).

    Layer 7-based custom application signatures detect applications based on the patterns in HTTP contexts. However, some HTTP sessions are encrypted in SSL, also called Transport Layer Security (TLS). Application identification can extract the server name information or the server certification from the TLS or SSL sessions. It can also detect patterns in TCP or UDP payload in Layer 7 applications.