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## Types of Firewall Services

The SRC software represents a JUNOS firewall as two types of SRC services:

- Basic firewall service—Defines the action that the firewall takes and specifies the types of traffic that the firewall affects.
- Services to provide firewall exceptions—Defines exception rules to block traffic that otherwise would be permitted to traverse the firewall, or to admit traffic that would otherwise be blocked. Exceptions specify criteria against which packets and application flows are inspected.

For example, to configure an access only to accept e-mail from a specific IP address, you can use a basic firewall service that blocks all incoming and outgoing traffic; then you can use a firewall exception that allows incoming e-mail traffic from that IP address.

The SRC software supports the following types of firewalls on JUNOS routing platforms:

- Stateless firewalls—Inspect each packet in isolation; do not evaluate the traffic flow.
- Stateful firewalls—Inspect track traffic flows and conversations between applications, and evaluate this information when applying exception rules to the traffic.

  An application is typically associated with a stateful firewall rule. After a flow or conversation meets firewall criteria, packets in that flow can pass through the firewall. For example, when an FTP control connection requests a file download, the stateful firewall knows to expect and allows a TCP data connection to start.

  The same criteria may not be applied to each packet. For example for a TCP application, the criteria changes when a new TCP session is initiated to allow subsequent packets in the flow.

You can make either stateless firewalls or stateful firewalls available from Enterprise Manager Portal.

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