Stateful and Stateless Data Processing

Traffic that enters and exits a Services Router running JUNOS software is processed according to features you configure, such as security policies, packet filters, and screens. For example the software can determine:

• Whether the packet is allowed into the router
• Which class of service (CoS) to apply to the packet, if any
• Which firewall screens to apply to the packet
• Whether to send the packet through an IPsec tunnel
• Whether the packet requires an Application Layer Gateway (ALG)
• Whether to apply Network Address Translation (NAT) to translate the packet's address
• The route the packet takes to reach its destination.

Packets that enter and exit a Services Router running JUNOS software undergo both packet-based and flow-based processing.

• Flow-based, or stateful, packet processing treats related packets, or a stream of packets, in the same way. Packet treatment depends on characteristics that were established for the first packet of the packet stream, which is referred to as a flow.
• Packet-based, or stateless, packet processing treats packets discretely. Each packet is assessed individually for treatment.

The software implements flow-based security and services, with packet-based application of filters, policers, traffic shapers, and other classification features.

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