It looks like https://github.com/apache/jmeter/pull/524#issuecomment-538478304
I think I know what is going on there. TL;DR: it is Apache HTTP Client's bug: "wrong interface is used for DNS resolution when source IP is specified" @ham1 , @Felix would you please add `localIp` to `Assertions.assertEquals` message (the 3rd argument) and provide the new message? Could you please provide the output of `ping localhost` and `ping6 localhost`? 1) The whole nature of the test is to verify how HTTP client supports "the use of the specified source IP address" feature. In other words, HTTP Sampler has "source IP" field, which is propagated to the HTTP implementation. It is expected that JMeter should be able to send requests from the specified IP. That might help to load a single interface only, or to overcome 65536 ports per IP address limit or whatever. 2) Certain machines have both IPv4 and IPv6 at the same time. So far so good. WireMock listens on ALL the available interfaces. 3) Java's HTTP client does not have "source IP" feature, so it is not really tested. 4) Apache's HTTP client has the "source ip" feature. However, we tell it "ok, use this ipv6 as a source IP and connect to localhost:33099". Theoretically, it should work. However, in practice, Apache HTTP client might easily resolve `localhost` as `127.0.0.1`. Of course, it can't really connect to `127.0.0.1` via IPv6, so we see `Network is unreachable`. We can work around that by using explicit IP address (127.1 for ipv4) and (::1 for ipv6) instead of localhost, but we might want to raise a bug for HTTP Client. Vladimir
