Tips to Debug CURL with a client - (56) Recv failure: Connection reset by peer s...

A client of mine is trying to connect to our site via CURL. The command they are running is:

curl -Ik example.com

The response they receive is:

(56) Recv failure: Connection reset by peer site

They feel this response implies the issue must be on our end. That the connection is making it to us and we are rejecting it.

We run that same command from any machine outside their network (both local and remote) and get a successful response. Plus none of our other clients have this issue. So we feel the issue is likely on their end.

Really what I need is help to debug this. This client will run any test to help figure this out. Any suggestions?

If you ask the customer to curl from outside their firewall they should be able to get to you. The error from curl is misleading. Any hop in between could be considered peer site. Here, peer doesn't mean the destination.

It's best to ask their network engineer view the firewall log live, filtered for the destination address. When they curl, it should show on the firewall whether it's denied or allowed.