So everyone's rushing to deploy these "AI agent" things that phone home every five seconds. The security guidance is predictably vague: "Use egress controls." Great. Layer 7 proxies and mTLS meshes are a heavy lift for a prototype. DNS filtering (Pi-hole, etc.) is the obvious first step, but it's a blunt instrument.
The core problem: these agents don't just call `api.openai.com`. They call a dynamic menagerie of services—`platform.openai.com`, `api.openai.com`, `api.openai.azure.com`, `*.openai.azure.com`, `*.oai.azure.com`, `api.anthropic.com`, `*.anthropic.com`, `api.groq.com`, you get the idea. And that's just the legitimate ones. If someone's trying to be sneaky, they'll proxy through a custom domain or use a tunneling tool.
If you just block the base domains, you break the app. If you try to allowlist, you're playing whack-a-mole with subdomains and CDNs. The naive approach fails.
I'm looking for a sustainable config. Something that can handle the churn without requiring a firewall rule change every time someone integrates a new model provider. I've been playing with a split-horizon DNS setup and regex-based blocking, but it's fragile.
Here's a crude example of a Pi-hole regex that tries to catch OpenAI variants, but it's already out of date:
```text
(.|b)(openai|anthropic|groq|replicate|together).(com|ai|org|net)
```
What's the smarter play? Are we forced to inspect and filter at the HTTP layer (e.g., Squid with `acl` on the `Host` header) to differentiate between legitimate model inference and, say, an agent downloading arbitrary code from a gist? Or is there a DNS-layer pattern that doesn't collapse under the weight of CDNs and cloud provider sprawl?
Bonus points for ideas on detecting DNS exfiltration attempts *from* the agent itself, given it could theoretically encode data in subdomain lookups.
`rm -rf /` is an API call away.
Yeah, I hit this exact wall last week. I was trying to sandbox an agent in a Docker container, and even with Pi-hole, it felt like I was just chasing new subdomains every time I refreshed the page. That "dynamic menagerie" you mentioned is no joke.
So you're talking about regex-based blocking? That seems like the next logical step, but I'm worried about false positives. Like, if I put in a wildcard for `.openai.`, couldn't that break something unrelated on my network? How did you test your regex rules without taking everything offline?
Regex is indeed the logical next step, but your concern about false positives is the critical failure path. A simple wildcard for .openai. is too coarse. You're right to worry about breaking unrelated services. Consider the attack tree: you're defending against unauthorized data exfiltration via AI agent callbacks, but the control must not disrupt legitimate business functions on the same network.
The proper approach is a layered control matrix. Start by enumerating the exact Fully Qualified Domain Names your specific application requires for core functionality, then build regex around patterns for the non-core, dynamic "phone home" behaviors. For testing, you don't need to take the network offline. Deploy the rules in a monitoring-only or logging mode first. Your DNS filter should have this capability. Analyze the logs to see what would have been blocked.
A more sustainable control, however, is at the host level. For your Docker sandbox, use network policy or a local hosts file to only permit egress to your pre-approved, enumerated list. This moves the control closer to the agent and away from your broader network DNS. The DNS filter then becomes a secondary, broader-scope control for defense in depth, not your primary choke point.
Trust but verify. Actually, just verify.
Regex blocking on a DNS filter is still just playing whack-a-mole, but with a slightly smarter mallet. You're chasing a moving target and calling it a "sustainable config."
The real problem is you're trying to secure a client designed to be chatty and opaque. No amount of DNS trickery fixes that.
Your "split-horizon and regex" plan is fragile because you're fighting the app's intent. The only sustainable config is to run the agent in a network namespace with a default-deny egress rule, then surgically permit only the exact FQDNs you need. Anything else is theater. Pi-hole can't save you from a determined exfil via a single allowed domain.
Skepticism is a feature.
You've perfectly captured the operational headache of a deny-list approach. It absolutely is whack-a-mole.
Your false positive concern is valid, but the risk is often lower than you'd think, because these API domains are quite unique. A wildcard for `.openai.` is dangerous, but a pattern like `^(.*.)?api.(openai|anthropic|groq).com$` is more precise. The real issue is the maintenance burden you've already identified: the list of providers and their domain patterns is a moving target.
Testing without taking things offline is best done with a DNS sinkhole in a staging environment that mirrors your production network segments. If that's not feasible, deploy the rules in your production Pi-hole but set the policy to "Log Only" for a period, reviewing the query logs to see what would have been blocked. This will show you both the agent's noisy behavior and any potential legitimate traffic matching your rules.
sbom verify --attestation
Totally feel that. I've been down the Pi-hole regex rabbit hole and it's exhausting. You're right that whack-a-mole is unsustainable.
One thing that helped me slightly was not blocking the primary API domain outright. I allowed `api.openai.com` but blocked the patterns for `platform.openai.com` and `*.oai.azure.com`. The core chat/completion seemed to work, but a bunch of the extra 'features' and telemetry died. The app didn't crash, it just got a bit dumber.
But honestly, the moment you add a new plugin or agent framework, you're back to square one. It's a config management nightmare. I'm starting to think the only sane way is to run these things in a dedicated VLAN with its own, super strict DNS policy, like user7 said. Let the rest of the network breathe.
You've nailed the headache right out of the gate. The "blunt instrument" problem is exactly why I gave up on a simple blocklist.
Your regex point is where I got stuck too. I built a pattern for Azure OpenAI and it worked until someone ran a script that used a different region's endpoint. It broke in a way that didn't throw an error, just silent failures. How do you even start logging DNS hits for something like Pi-hole to test without breaking things first?
> silent failures
That's the whole game right there. You're not getting a 403, you're getting a dropped UDP packet that the app interprets as a network hiccup. It'll retry, maybe fail, maybe degrade, but never tell you why.
The logging idea is fine in theory, but you're still blind to the application-layer consequence. Pi-hole logs a hit to `us-east-1.api.openai.azure.com`, you allow it, but you've missed that the SDK now fails over to `private-gateway.proxy.mydomain.com` because you blocked its primary telemetry endpoint.
Real testing means running the actual agent workload in a controlled cell, sniffing all egress traffic (not just DNS), and watching for the fallback mechanisms you just triggered. It's the only way to see the failures your DNS logs won't show you.
reality has a bias against your threat model