Glossary · Networking
Carrier-grade NAT (CGNAT)
Carrier-grade NAT (CGNAT) is network address translation run by an internet provider rather than in the customer's router: many subscribers share one public IPv4 address and are told apart by port, and RFC 6598 reserves 100.64.0.0/10 as the shared address space between the provider's NAT and its customers.
Reviewed 30 Oct 2026
How CGNAT works
IPv4 addresses ran short long ago — RFC 6598, from 2012, already describes the space as nearly exhausted — so providers translate a second time inside their own network. The customer's router gets an address from 100.64.0.0/10 instead of a public one, and the carrier's NAT maps many such customers onto a smaller set of public addresses.
RFC 6888 sets the default that a CGN uses the same external address for all of one subscriber's sessions (paired pooling), so a single customer does not appear to hop between addresses while the address itself is shared with others.
Why it matters for data collection
- One address, many people. Blocking or throttling a CGNAT address affects every subscriber behind it, which is why carrier ranges are usually handled cautiously — the property a mobile proxy is bought for.
- Coarser reputation. Anything a site infers per address is an average over many users.
- Location is approximate. The public address belongs to the carrier's NAT, not the subscriber's home, which is one reason geo-targeting on carrier networks stops at country level on ARC Mobile. Check what an exit looks like from outside with the test proxy location guide.
How to tell if a connection is behind CGNAT
Compare the WAN address your router reports with the address an external IP-echo service sees. If the router's address is in 100.64.0.0/10 — 100.64.0.0 to 100.127.255.255 — and differs from the public one, the provider is translating for you.
FAQ
Questions
Something not covered? Write to contact@arcproxies.io.
Is 100.64.x.x a private IP address?
Not in the RFC 1918 sense. 100.64.0.0/10 is shared address space reserved by RFC 6598 for use between a provider's carrier-grade NAT and its customers. It is not routed on the public internet, but it is distinct from the 10/8, 172.16/12 and 192.168/16 private ranges.
Do mobile networks use CGNAT?
CGNAT is common on mobile networks for IPv4, where a carrier's subscribers share public addresses. That sharing is why a single mobile address often represents many devices at once.
Why does CGNAT make IP blocking harder?
Because a public address behind CGNAT represents many unrelated subscribers. Blocking it to stop one client also blocks the rest, so sites tend to rely on signals other than the address when traffic comes from carrier ranges.
Sources & review
Last reviewed by the ARC Proxies team. Prices are read from the live catalog at build time.
In practice