Are you running Java 7 on OS X? If so, you might be experiencing the same bug as reported in [1]. I don't believe this is a logback issue.

I reproduced the exception using the snippet from [1] and JDK 7:

    import java.net.InetAddress;

    public class InetAddressTest {
     public static void main(String... args) throws Exception {
     System.out.println("InetAddress.getLocalHost() = " + InetAddress.getLocalHost());
     }
    }

The problem does not occur with JDK 6.

[1] http://java.net/jira/browse/MACOSX_PORT-564

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