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https://issues.apache.org/jira/browse/HDFS-4043?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17579133#comment-17579133
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ASF GitHub Bot commented on HDFS-4043:
--------------------------------------

snmvaughan commented on code in PR #4693:
URL: https://github.com/apache/hadoop/pull/4693#discussion_r944850020


##########
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/net/DNSDomainNameResolver.java:
##########
@@ -40,6 +48,16 @@ public String getHostnameByIP(InetAddress address) {
         && host.charAt(host.length()-1) == '.') {
       host = host.substring(0, host.length()-1);
     }
+    // Protect against the Java behaviour of returning the IP address as a 
string from a cache
+    // instead of performing a reverse lookup.
+    if (host.equals(address.getHostAddress())) {
+      LOG.debug("IP address returned for FQDN detected");

Review Comment:
   I'll make that change.





> Namenode Kerberos Login does not use proper hostname for host qualified hdfs 
> principal name.
> --------------------------------------------------------------------------------------------
>
>                 Key: HDFS-4043
>                 URL: https://issues.apache.org/jira/browse/HDFS-4043
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: security
>    Affects Versions: 2.0.0-alpha, 2.0.1-alpha, 2.0.2-alpha, 2.0.3-alpha, 
> 3.4.0, 3.3.9
>         Environment: CDH4U1 on Ubuntu 12.04
>            Reporter: Ahad Rana
>            Priority: Major
>              Labels: pull-request-available
>   Original Estimate: 24h
>          Time Spent: 50m
>  Remaining Estimate: 23h 10m
>
> The Namenode uses the loginAsNameNodeUser method in NameNode.java to login 
> using the hdfs principal. This method in turn invokes SecurityUtil.login with 
> a hostname (last parameter) obtained via a call to InetAddress.getHostName. 
> This call does not always return the fully qualified host name, and thus 
> causes the namenode to login to fail due to kerberos's inability to find a 
> matching hdfs principal in the hdfs.keytab file. Instead it should use 
> InetAddress.getCanonicalHostName. This is consistent with what is used 
> internally by SecurityUtil.java to login in other services, such as the 
> DataNode. 



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