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No IPv4 on your router's WAN? DS-Lite, 464XLAT and MAP-T explained

Some ISPs don't give your router an IPv4 address at all. The line runs on IPv6, and the ISP carries your IPv4 traffic across it while sharing IPv4 addresses between customers. Websites still load, but for hosting anything over IPv4 it usually behaves like CGNAT.

How to spot it

• The router's WAN or internet status shows an IPv6 address or prefix but no IPv4 address, yet IPv4-only sites still work.
• The router's IPv4 address is 192.0.0.2 or another address in 192.0.0.0/29. That small range is reserved for these methods: DS-Lite uses 192.0.0.2 on the customer side and 192.0.0.1 on the ISP side by default (RFC 6333, section 5.7), and the reservation was later widened to cover similar methods such as 464XLAT (RFC 7335).
• The status page names the method: look for words like DS-Lite, AFTR, MAP-T, MAP-E, BR, 464XLAT or CLAT.
• The public IPv4 that websites see isn't on your router anywhere. The CGNAT checker shows your public IPv4 and IPv6 so you can compare.

If your router does show an IPv4 address in 100.64.0.0/10 instead, that's classic CGNAT: see the 100.64.0.0/10 range explained.

The common methods

• DS-Lite (Dual-Stack Lite). Your router wraps IPv4 packets inside IPv6 and sends them to a box in the ISP's network that does the address sharing (NAT) for many customers at once. The standard describes it as combining IPv4-in-IPv6 and NAT so a provider can share IPv4 addresses among customers (RFC 6333, section 1). For self-hosting it's the same as CGNAT: the NAT sits at the ISP, not on your router.
• Lightweight 4over6. A variant of DS-Lite that moves the address sharing onto your router: you get a shared public IPv4 and a slice of its ports (RFC 7596, section 1).
• MAP-E and MAP-T. Your router gets a shared public IPv4 address and a fixed set of its ports, worked out from your IPv6 prefix. MAP-E wraps IPv4 inside IPv6; MAP-T translates it instead (RFC 7597, section 4; RFC 7599, section 1). The ISP decides how many customers share an address, and it can leave the well-known low-numbered ports out of what customers get (RFC 7597, section 5.1). The same method can also hand a customer a full, unshared IPv4.
• 464XLAT. Common on mobile and fixed-wireless networks. Your device or router translates IPv4 into IPv6, and the ISP translates it back to IPv4 with a shared address (RFC 6877, section 1; the ISP-side translation is stateful NAT64, RFC 6146). The standard itself says it only supports IPv4 where you connect out to a server, and isn't suitable for peer-to-peer or incoming IPv4 connections.

What it means for self-hosting

• Incoming IPv4 on DS-Lite or 464XLAT: blocked, as with CGNAT. Port forwarding on your router can't reach through the ISP's NAT. The DS-Lite standard points to a protocol for apps to ask the ISP's NAT to open a port (RFC 6333, section 8.5), but whether that's offered is up to the ISP.
• Incoming IPv4 on MAP-E, MAP-T or Lightweight 4over6: can work, but only on ports inside your assigned range. Services that need a fixed, well-known port, like a web server on 80 or 443 or a mail server on 25, usually can't use it if that port isn't yours.
• Incoming IPv6: these lines are IPv6-native, so your devices usually get real, reachable IPv6 addresses. 464XLAT, for example, keeps full any-to-any IPv6 (RFC 6877, section 1). Hosting over IPv6 can work if your router's IPv6 firewall allows it, but visitors who only have IPv4 can't reach you that way.
• Outgoing connections: browsing, streaming and most apps work normally over both IPv4 and IPv6.

Is my US ISP doing this?

Few US ISPs document it. Customer reports (not confirmed by the ISPs) say T-Mobile Home Internet runs IPv6-only with 464XLAT, and that some Cox and Spectrum areas use MAP-T. Each ISP page links its sources. If you can confirm what your line uses, send a report.

What to ask your ISP

1. "Is my line on DS-Lite, MAP-T, MAP-E or 464XLAT? Can you move me to dual-stack with a full public IPv4?" Customer reports say some ISPs will switch a line on request (see the Cox page).
2. "Do you sell a static IP on residential plans?" A static IPv4 is never shared.
3. "Do I get a routed IPv6 prefix, and can I allow incoming connections to it?" On these lines IPv6 is usually the easy path for hosting.

Compare providers on the ISPs without CGNAT list or filter the ISP finder for no CGNAT plus IPv6. For what breaks by use case, see self-hosting behind CGNAT.

FAQ

Why does my router show no IPv4 address?

Your ISP may deliver IPv4 over an IPv6-only line using DS-Lite, 464XLAT or a similar method. Your devices still reach IPv4 sites, but the ISP shares IPv4 addresses between customers, so your router never gets one of its own.

What does 192.0.0.2 on my router mean?

Addresses in 192.0.0.0/29 are reserved for these IPv4-over-IPv6 methods. DS-Lite uses 192.0.0.2 on the customer side by default, and the range was later opened to similar methods such as 464XLAT. It means your IPv4 is carried over IPv6 and shared, not a public address.

Can I host a server on DS-Lite or 464XLAT?

Not over IPv4, unless your ISP opens ports for you: incoming IPv4 connections stop at the ISP's NAT, as with CGNAT. Over IPv6 you can, if your router's IPv6 firewall allows it and your visitors have IPv6.

Is MAP-T better than CGNAT for port forwarding?

Somewhat. With MAP-T or MAP-E your router gets a shared public IPv4 and its own fixed range of ports, so forwarding can work on ports inside that range. The ISP picks the range, and well-known ports such as 25, 80 and 443 may not be in it.

How do I get a normal public IPv4?

Ask your ISP to move your line to dual-stack with a full public IPv4, or whether it sells a static IP. Customer reports say some ISPs will switch a line on request.

Sources

• RFC 6333: Dual-Stack Lite Broadband Deployments Following IPv4 Exhaustion (IETF, August 2011)
• RFC 7335: IPv4 Service Continuity Prefix (IETF, August 2014)
• RFC 6877: 464XLAT: Combination of Stateful and Stateless Translation (IETF, April 2013)
• RFC 6146: Stateful NAT64 (IETF, April 2011)
• RFC 7596: Lightweight 4over6: An Extension to the Dual-Stack Lite Architecture (IETF, July 2015)
• RFC 7597: Mapping of Address and Port with Encapsulation (MAP-E) (IETF, July 2015)
• RFC 7599: Mapping of Address and Port using Translation (MAP-T) (IETF, July 2015)

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