What is DS-Lite?
DS-Lite (Dual-Stack Lite) is an IPv4-to-IPv6 transition technology developed by the IETF. It enables ISPs to provide IPv4 access over an IPv6 network without assigning a public IPv4 address to each user.
The problem DS-Lite solves
The acute shortage of IPv4 addresses. In most regions, the IPv4 pool is exhausted. DS-Lite solves this by:
- The client has IPv6 only
- IPv4 traffic is tunneled over IPv6 to CGNAT
- CGNAT performs NAT44 and sends packets into the IPv4 network
How DS-Lite works
Components:
- B4 (Basic Bridging BroadBand) — client-side on the CPE
- AFTR (Address Family Transition Router) — provider-side CGNAT server
Mechanics:
- The subscriber’s device receives only IPv6
- IPv4 packets are encapsulated into IPv6 (inside B4)
- Sent to AFTR via tunnel
- AFTR decapsulates IPv4, applies NAT44, and routes
Advantages
- No need to allocate public IPv4
- Centralized NAT simplifies audit and control
- Seamless experience for subscribers
Disadvantages
- Some applications (VPN, VoIP) may conflict with NAT44
- Requires DS-Lite support on CPE and BNG
FAQ
Is DS-Lite a NAT?
Partially. The client has no NAT. NAT44 is performed centrally at the AFTR.
Is DS-Lite supported in Mikrotik?
No. Mikrotik does not support B4 mode. You need third-party firmware or a CPE replacement.
Alternatives to DS-Lite?
- NAT64 + DNS64
- MAP-E (slow adoption)
Conclusion
DS-Lite is a practical choice for ISPs looking to deploy large-scale IPv6 networks without losing IPv4 content access. It scales well, is compatible with CGNAT, and conserves scarce IPv4 resources.
