What is CGNAT in mobile internet? In many mobile networks you don’t get a “clean” public IPv4 directly on your device or 4G/5G router. Instead, your traffic goes through Carrier‑Grade NAT (CGNAT) inside the carrier. That means one public IPv4 is shared by many subscribers. From the outside you blend into a large crowd, and your outbound IPv4 can change more often than with typical home broadband.
In mobile proxy use cases (SMM, ads, scraping, geo QA), CGNAT creates a common trade‑off: shared mobile IPv4 often boosts trust because it looks like consumer traffic, but it hurts IP whitelisting because allowlists expect stability. Below is a practical breakdown: how shared IP reputation works, why “neighbor” traffic matters, when you want sticky sessions vs rotation, and what to offer clients who insist on whitelists.
1) How CGNAT works (NAT on top of NAT)
At home, your router does NAT: your devices use private IPs, and the whole home exits via one public IPv4. Mobile carriers often add another NAT layer at carrier scale (often called NAT444). Subscriber addressing may use the 100.64.0.0/10 “shared address space”, while a smaller pool of public IPv4 is shared externally.
To tell subscribers apart on the same public IPv4, CGNAT typically relies on port translation (PAT/NAPT). In practice, your “public identity” is not just the IP address, but also external ports and session timing.
2) Why shared mobile IPv4 can improve trust
Many anti‑abuse systems treat mobile networks differently from data centers. Mobile ASNs, mixed real‑user background traffic, and natural churn can make an IP look “human”. In many workflows that translates to:
- Carrier ASN signals “not a hosting provider”.
- Real‑world session patterns that resemble consumer usage.
- Rotation can reduce long‑term buildup of suspicion on a single address (when your behavior remains compliant).
3) Shared reputation: how neighbors can get you flagged
Shared IP means shared reputation. If other users on the same public IPv4 generate spam, abusive scraping, or high‑velocity logins, the IP can be downgraded and you get collateral friction:
- Blocklists triggered by spam/abuse reports.
- Higher challenge rates (CAPTCHA, step‑up auth, 429 limits).
- Automation heuristics triggered by many logins from one IP.
This doesn’t make CGNAT “bad”; it means you need rate limits, profiles, and the right session mode for the job.
4) Why IP allowlisting often fails under CGNAT
IP whitelisting works only when the public IP is stable. Under CGNAT it is often unstable by design:
- Public IPv4 changes due to load balancing, reconnection, or network events.
- Port variability can affect NAT traversal and some security assumptions.
- Collateral trust concerns: some services treat heavily shared IPs as higher risk even if allowlisted.
5) Sticky sessions vs rotating IPs
Sticky means you keep the same outbound IP for as long as possible. Rotation means you deliberately change it on a schedule or on demand.
Use sticky when:
- You have login sessions where an IP change triggers challenges (social platforms, ad accounts, marketplaces).
- You need a stable browsing/admin session with session tokens.
- You must temporarily satisfy an allowlist requirement (for minutes/hours).
Use rotation when:
- You do scraping/monitoring and want to reduce per‑IP rate pressure.
- You run geo QA and need multiple exits.
- You want a quick escape from 429/CAPTCHA on a “tired” IP.
6) How to explain this to clients (simple and actionable)
- What it is: “Mobile carriers share one IPv4 across many users using CGNAT.”
- Why it helps: “It looks like normal mobile consumer traffic, often improving trust.”
- Where it hurts: “The public IP can change, so IP‑based whitelists are unstable.”
- What we offer: “Sticky sessions, dedicated mobile IP where possible, or alternative allowlisting methods.”
7) Practical solutions when a whitelist is mandatory
- Static egress gateway: clients connect to your gateway/proxy with a fixed public IP. The gateway then routes traffic into the mobile network. Whitelist works on the gateway IP, but the service sees a data‑center address.
- Dedicated public mobile IPv4: sometimes available via specific carrier products/partners. Best of both worlds (mobile ASN + stability), but costs more and is not always available.
- Identity‑based allowlisting: mTLS, signed requests, OAuth, rotating API keys—IP becomes an additional factor, not the single lock.
- IPv6: if the target supports IPv6, allowlisting might be possible there, with attention to privacy addressing behavior.
8) Provider hygiene: reduce “neighbor risk”
- Shard pools to avoid too many clients sharing the same public IP at once.
- Rate limit and backoff on 429/403 responses.
- Separate SMM (sticky) from scraping (rotation + pacing) profiles.
- Monitor reputation signals: CAPTCHA share, blocklists, domain anomalies.