MongoDB+MCP+ServerSelectionTimeoutError+against+Atlas+IP+not+on+the+access

Not specified by the original author.

TL;DR: Timeouts against Atlas almost always mean your IP is not on the Atlas access list. Atlas drops the packets silently, so the driver just times out. Go to Network Access in the Atlas dashboard and add your current IP.

MongoServerSelectionError: connection timed out

Fix it

1. In the Atlas dashboard, open Network Access for your project and check the IP access list.
2. Add your current public IP. Find it with:

curl -s https://api.ipify.org

Add it as a single IP entry. For a quick test you can use the all-interfaces address/0 (allow from anywhere), but replace it with your real IP afterward.

3. Wait a minute for the change to propagate, then restart the MCP client or retry the tool call.

   Expected: the server connects within seconds and tools respond.

When to use this

• Local MongoDB (mongodb://YOUR_HOST:27017) works, but the Atlas mongodb+srv:// URL times out.
• The timeout happens consistently, not intermittently.

When NOT to use this

• The error is bad auth or authentication failed. Your IP is fine; the credentials are wrong.
• The error mentions DNS or SRV lookup failures. That is a DNS problem, not the access list.

Compatibility

• mongodb-mcp-server against MongoDB Atlas (any tier).
• Any MongoDB driver, the failure mode is identical.

Why it happens

Atlas defaults to deny-all networking. Unlike a wrong password, which gets an explicit rejection, a non-allowlisted IP gets its packets dropped with no response. The driver's server-selection loop waits for a response that never comes and eventually reports a timeout, which misleads people into debugging DNS or drivers.

Edge cases

• Home IPs change. If it worked yesterday and times out today, your ISP rotated your IP. Re-add it.
• VPNs change your egress IP. Add the VPN exit IP, or disconnect the VPN for testing.
• the all-interfaces address/0 is fine for a five-minute test, not for production. Narrow it as soon as it works.

MongoDB Atlas blocks all connections from IPs not on the project's IP access list, and the driver surfaces this as a server selection timeout rather than a clear blocked message. This is the most common Atlas connectivity failure and the documented fix is adding the client IP (or the all-interfaces address/0 for testing) under Network Access in the Atlas dashboard. The mongodb-mcp-server README notes the connection string can point at any MongoDB cluster including Atlas, which is where this failure mode appears.

Not specified by the original author.

TL;DR: The driver found the cluster topology but could not establish a working connection to any node. On Atlas this is the IP access list nine times out of ten. Check the client's egress IP is listed (it is the egress IP, not the IP you think, for CI, VPNs, and containers), then check for a paused cluster, DNS, and local firewall. Then retry.

The error, verbatim:

ServerSelectionTimeoutError: [host]:[port] timed out
No suitable servers found

Steps:

1. IP access list: Security, Network Access in Atlas. Is the client's egress IP listed? Success: the egress IP is on the list (add it with an expiry for temporary access).
2. Cluster state: is the cluster paused? A paused cluster refuses connections with timeouts, not a clear error. Success: the cluster is running.
3. DNS: can the machine resolve the SRV record? nslookup -type=SRV _mongodb._tcp.[cluster-host]. If not, use the standard connection string form. Success: SRV resolves or the standard string works.
4. Local firewall or proxy blocking outbound 27017. Success: the port is reachable.
5. Retry with a startup ping from the failing network. Success: the ping succeeds.

When to use: ServerSelectionTimeoutError or no suitable servers against MongoDB Atlas.

When not to use: authentication failures (wrong error), malformed connection strings, or self-hosted replica sets (different failure modes).

Compatibility: MongoDB drivers (any language), MongoDB Atlas.

Variants:

• mongodb atlas connection timeout
• no suitable servers found atlas
• serverselectiontimeouterror atlas fix

Root cause: the driver knows where the cluster is but cannot open a socket to any node. Atlas's network gate is the access list, and the client IP is almost always the surprise: CI runners, VPNs, and containers egress from IPs nobody configured.

Edge cases:

• It works from your laptop but not the deploy target: the difference is the network path, and the IP access list is still suspect number one.
• A paused cluster looks exactly like a network failure. Check state before debugging DNS.
• For temporary access, add the IP with an expiry so the list does not accumulate stale entries.

Server selection failure causes and the troubleshooting order (IP access list first, then cluster state, DNS, firewall) per https://www.mongodb.com/docs/atlas/troubleshoot-connection/ and https://www.mongodb.com/docs/atlas/security/ip-access-list/, verified 2026-09-26.

Not specified by the original author.

TL;DR

Add the egress IP of wherever the agent runs. Atlas UI: Security, Network Access, Add IP Address.

Steps

1. Atlas UI: Security, Network Access, Add IP Address.
2. Add the egress IP of wherever the agent runs. For a laptop, use Add Current IP Address.
3. Give temporary entries an expiry (a week for a laptop, a day for a debug session) so stale IPs do not accumulate.

When to use

You are seeing this: Atlas blocks every IP until you allow it. Use this skill when you run into "MongoDB Atlas: IP access list setup for agents and CI".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.

IP access list behavior (default deny, entry management, expiry) verified against https://www.mongodb.com/docs/atlas/security/ip-access-list/ on 2026-09-26; connection troubleshooting order per https://www.mongodb.com/docs/atlas/troubleshoot-connection/.