Java getInputStream SocketTimeoutException instead of NoRouteToHostException

I have an odd issue happening when trying to open multiple Input Streams (in separate threads) on Linux (RHEL). The behaviour works as expected on windows.

I am kicking off 3 threads to open https connections to 3 different servers. All three are invalid IP addresses (in this test case), so I expect an NoRouteToHostException for each of them. The first two return these as expected, and quite quickly. (see stack trace below) However the third (and 4th when I tested it that way) do NOT give a no route exception. They wait for ages, and then give a SocketTimeoutException (see other stack trace below). This takes ages to come back, and does not accurately express the connection issue.

The offending line of code is:

reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));

Has anyone seen something like this before? Are there multi-threading issues with sockets on REHL or some limit somewhere to how many can connect at once...or...something?

Expected stack trace, as received for first two:

java.net.NoRouteToHostException: No route to host
        at java.net.PlainSocketImpl.socketConnect(Native Method)
        at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)
        at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)
        at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)
        at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
        at java.net.Socket.connect(Socket.java:529)
        at com.sun.net.ssl.internal.ssl.SSLSocketImpl.connect(SSLSocketImpl.java:559)
        at sun.net.NetworkClient.doConnect(NetworkClient.java:158)
        at sun.net.www.http.HttpClient.openServer(HttpClient.java:394)
        at sun.net.www.http.HttpClient.openServer(HttpClient.java:529)
        at sun.net.www.protocol.https.HttpsClient.(HttpsClient.java:272)
        at sun.net.www.protocol.https.HttpsClient.New(HttpsClient.java:329)
        at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.getNewHttpClient(AbstractDelegateHttpsURLConnection.java:172)
        at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:916)
        at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:158)
        at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1177)
        at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:234)

Unexpected stack trace, as received on 3rd:

java.net.SocketTimeoutException: connect timed out
        at java.net.PlainSocketImpl.socketConnect(Native Method)
        at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)开发者_StackOverflow中文版
        at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)
        at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)
        at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
        at java.net.Socket.connect(Socket.java:529)
        at com.sun.net.ssl.internal.ssl.SSLSocketImpl.connect(SSLSocketImpl.java:559)
        at sun.net.NetworkClient.doConnect(NetworkClient.java:158)
        at sun.net.www.http.HttpClient.openServer(HttpClient.java:394)
        at sun.net.www.http.HttpClient.openServer(HttpClient.java:529)
        at sun.net.www.protocol.https.HttpsClient.(HttpsClient.java:272)
        at sun.net.www.protocol.https.HttpsClient.New(HttpsClient.java:329)
        at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.getNewHttpClient(AbstractDelegateHttpsURLConnection.java:172)
        at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:916)
        at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:158)
        at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1177)
        at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:234)

Is the linux firewall blocking the connect? If the output of iptables -L is populated that may contain your answer. You can also test by using telnet localhost <portnumber> to check if the port is available. If it is, telnet should say "connected", etc.

If the invalid IP address is blackholed, then no response will come back, and you will get a timeout rather than a "no route to host". The latter relies upon an ICMP error message being received back from the network.

Ah. see now I feel rather silly. Prompted from the responses above I decided to just put the ip addresses into the browser and see what happened. It turns out I was using the following IP addresses: 1.1.1.1 2.2.2.2 3.3.3.3

Unfortunately, 3.3.3.3 IS a valid IP address, which is not responding. So infact it was working fine all along.

I am now using proper non routable IP addresses 10.27.1.1 etc.