diff --git a/clients/src/main/java/org/apache/kafka/clients/ClientUtils.java b/clients/src/main/java/org/apache/kafka/clients/ClientUtils.java
index 0c12ea13450..2672b701aaf 100644
--- a/clients/src/main/java/org/apache/kafka/clients/ClientUtils.java
+++ b/clients/src/main/java/org/apache/kafka/clients/ClientUtils.java
@@ -38,24 +38,26 @@ public class ClientUtils {
     public static List<InetSocketAddress> parseAndValidateAddresses(List<String> urls) {
         List<InetSocketAddress> addresses = new ArrayList<InetSocketAddress>();
         for (String url : urls) {
-            if (url != null && url.length() > 0) {
-                String host = getHost(url);
-                Integer port = getPort(url);
-                if (host == null || port == null)
-                    throw new ConfigException("Invalid url in " + CommonClientConfigs.BOOTSTRAP_SERVERS_CONFIG + ": " + url);
+            if (url != null && !url.isEmpty()) {
                 try {
+                    String host = getHost(url);
+                    Integer port = getPort(url);
+                    if (host == null || port == null)
+                        throw new ConfigException("Invalid url in " + CommonClientConfigs.BOOTSTRAP_SERVERS_CONFIG + ": " + url);
+
                     InetSocketAddress address = new InetSocketAddress(host, port);
+
                     if (address.isUnresolved()) {
-                        log.warn("Removing server from " + CommonClientConfigs.BOOTSTRAP_SERVERS_CONFIG + " as DNS resolution failed: " + url);
+                        log.warn("Removing server {} from {} as DNS resolution failed for {}", url, CommonClientConfigs.BOOTSTRAP_SERVERS_CONFIG, host);
                     } else {
                         addresses.add(address);
                     }
-                } catch (NumberFormatException e) {
+                } catch (IllegalArgumentException e) {
                     throw new ConfigException("Invalid port in " + CommonClientConfigs.BOOTSTRAP_SERVERS_CONFIG + ": " + url);
                 }
             }
         }
-        if (addresses.size() < 1)
+        if (addresses.isEmpty())
             throw new ConfigException("No resolvable bootstrap urls given in " + CommonClientConfigs.BOOTSTRAP_SERVERS_CONFIG);
         return addresses;
     }
diff --git a/clients/src/main/java/org/apache/kafka/common/utils/Utils.java b/clients/src/main/java/org/apache/kafka/common/utils/Utils.java
index 8d7014a705a..1bbfea93f10 100755
--- a/clients/src/main/java/org/apache/kafka/common/utils/Utils.java
+++ b/clients/src/main/java/org/apache/kafka/common/utils/Utils.java
@@ -51,7 +51,7 @@ public class Utils {
 
     // This matches URIs of formats: host:port and protocol:\\host:port
     // IPv6 is supported with [ip] pattern
-    private static final Pattern HOST_PORT_PATTERN = Pattern.compile(".*?\\[?([0-9a-zA-Z\\-%.:]*)\\]?:([0-9]+)");
+    private static final Pattern HOST_PORT_PATTERN = Pattern.compile(".*?\\[?([0-9a-zA-Z\\-%._:]*)\\]?:([0-9]+)");
 
     public static final String NL = System.getProperty("line.separator");
 
diff --git a/clients/src/test/java/org/apache/kafka/common/utils/UtilsTest.java b/clients/src/test/java/org/apache/kafka/common/utils/UtilsTest.java
index 1af7e43f8e9..46400b4a634 100755
--- a/clients/src/test/java/org/apache/kafka/common/utils/UtilsTest.java
+++ b/clients/src/test/java/org/apache/kafka/common/utils/UtilsTest.java
@@ -38,6 +38,7 @@ public class UtilsTest {
         assertEquals("127.0.0.1", getHost("127.0.0.1:8000"));
         assertEquals("mydomain.com", getHost("PLAINTEXT://mydomain.com:8080"));
         assertEquals("MyDomain.com", getHost("PLAINTEXT://MyDomain.com:8080"));
+        assertEquals("My_Domain.com", getHost("PLAINTEXT://My_Domain.com:8080"));
         assertEquals("::1", getHost("[::1]:1234"));
         assertEquals("2001:db8:85a3:8d3:1319:8a2e:370:7348", getHost("PLAINTEXT://[2001:db8:85a3:8d3:1319:8a2e:370:7348]:5678"));
         assertEquals("2001:DB8:85A3:8D3:1319:8A2E:370:7348", getHost("PLAINTEXT://[2001:DB8:85A3:8D3:1319:8A2E:370:7348]:5678"));
diff --git a/core/src/main/scala/kafka/cluster/BrokerEndPoint.scala b/core/src/main/scala/kafka/cluster/BrokerEndPoint.scala
index 99cf66688b0..91823f086c4 100644
--- a/core/src/main/scala/kafka/cluster/BrokerEndPoint.scala
+++ b/core/src/main/scala/kafka/cluster/BrokerEndPoint.scala
@@ -24,7 +24,7 @@ import org.apache.kafka.common.utils.Utils._
 
 object BrokerEndPoint {
 
-  private val uriParseExp = """\[?([0-9a-zA-Z\-%.:]*)\]?:([0-9]+)""".r
+  private val uriParseExp = """\[?([0-9a-zA-Z\-%._:]*)\]?:([0-9]+)""".r
 
   /**
    * BrokerEndPoint URI is host:port or [ipv6_host]:port
diff --git a/core/src/main/scala/kafka/cluster/EndPoint.scala b/core/src/main/scala/kafka/cluster/EndPoint.scala
index eb45aae54c5..720d8196266 100644
--- a/core/src/main/scala/kafka/cluster/EndPoint.scala
+++ b/core/src/main/scala/kafka/cluster/EndPoint.scala
@@ -26,7 +26,7 @@ import org.apache.kafka.common.utils.Utils
 
 object EndPoint {
 
-  private val uriParseExp = """^(.*)://\[?([0-9a-zA-Z\-%.:]*)\]?:(-?[0-9]+)""".r
+  private val uriParseExp = """^(.*)://\[?([0-9a-zA-Z\-%._:]*)\]?:(-?[0-9]+)""".r
 
   def readFrom(buffer: ByteBuffer): EndPoint = {
     val port = buffer.getInt()
diff --git a/core/src/test/scala/unit/kafka/cluster/BrokerEndPointTest.scala b/core/src/test/scala/unit/kafka/cluster/BrokerEndPointTest.scala
index cec8fec1f1f..5554b39eac5 100644
--- a/core/src/test/scala/unit/kafka/cluster/BrokerEndPointTest.scala
+++ b/core/src/test/scala/unit/kafka/cluster/BrokerEndPointTest.scala
@@ -97,6 +97,11 @@ class BrokerEndPointTest extends Logging {
     var endpoint = BrokerEndPoint.createBrokerEndPoint(1, connectionString)
     assert(endpoint.host == "localhost")
     assert(endpoint.port == 9092)
+    //KAFKA-3719
+    connectionString = "local_host:9092"
+    endpoint = BrokerEndPoint.createBrokerEndPoint(1, connectionString)
+    assert(endpoint.host == "local_host")
+    assert(endpoint.port == 9092)
     // also test for ipv6
     connectionString = "[::1]:9092"
     endpoint = BrokerEndPoint.createBrokerEndPoint(1, connectionString)
@@ -121,6 +126,12 @@ class BrokerEndPointTest extends Logging {
     assert(endpoint.host == "localhost")
     assert(endpoint.port == 9092)
     assert(endpoint.connectionString == "PLAINTEXT://localhost:9092")
+    // KAFKA-3719
+    connectionString = "PLAINTEXT://local_host:9092"
+    endpoint = EndPoint.createEndPoint(connectionString)
+    assert(endpoint.host == "local_host")
+    assert(endpoint.port == 9092)
+    assert(endpoint.connectionString == "PLAINTEXT://local_host:9092")
     // also test for default bind
     connectionString = "PLAINTEXT://:9092"
     endpoint = EndPoint.createEndPoint(connectionString)