This article provides information about the support extended for the DS-LITE feature by SRX firewalls.

The Softwire Initiator (SI) in the dual-stack lite is a home router,the Softwire Concentrator (SC) in the dual-stack lite is like a carrier-grade NAT Server device. 

SI is like a Client and SC is like a Server. When SI initiates the tunnel, SC can respond and take part in the traffic flow process,but SC cannot start Softwire.

A Softwire is a tunnel over IPv6 network. SI finds the SC address, encapsulates an IPv4 packet, and transmits it across a softwire. SC receives an IPv4-in-IPv6 softwire packet and decapsulates it to get the inner IPv4 packet. Multiple SIs can have the same SC as the end point of the softwires. In other words, it is a multipoint to point (MP2P) model.

Note : The dual-stack lite carrier-grade NAT performs IPv4-IPv4 NAT translations to multiplex multiple subscribers through a single global IPv4 address. Overlapping address spaces, which are used by subscribers, are disambiguated through the identification of tunnel endpoints.

SRX firewalls support only the Software Concentrator. For more information about the new features in Junos 12.1 for High-End SRX series services gateways, refer to the following link:

http://www.juniper.net/techpubs/en_US/junos12.1/information-products/topic-collections/release-notes/12.1/topic-64970.html

For more information about multiple features, refer to the following link:

http://pathfinder.juniper.net/search-features.html