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https://issues.apache.org/jira/browse/KAFKA-8562?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16912437#comment-16912437
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Manikumar commented on KAFKA-8562:
----------------------------------
Incase of SASL, hostname is used in
[SaslClientAuthenticator|https://github.com/apache/kafka/blob/trunk/clients/src/main/java/org/apache/kafka/common/network/SaslChannelBuilder.java#L203]
and
[SslTransportLayer|https://github.com/apache/kafka/blob/trunk/clients/src/main/java/org/apache/kafka/com]
instances.
I think incase of SaslClient, broker hostname must match with the hostname in
`principal/hostname@realm`. So we need to still do DNS lookup to resolve IP to
DNS. We can avoid the lookup while building underlyting SslTransportLayer
instance.
> SASL_SSL still performs reverse DNS lookup despite KAFKA-5051
> -------------------------------------------------------------
>
> Key: KAFKA-8562
> URL: https://issues.apache.org/jira/browse/KAFKA-8562
> Project: Kafka
> Issue Type: Bug
> Reporter: Badai Aqrandista
> Priority: Minor
>
> When using SASL_SSL, the Kafka client performs a reverse DNS lookup to
> resolve IP to DNS. So, this circumvent the security fix made in KAFKA-5051.
> This is the line of code from AK 2.2 where it performs the lookup:
> https://github.com/apache/kafka/blob/2.2.0/clients/src/main/java/org/apache/kafka/common/network/SaslChannelBuilder.java#L205
> Following log messages show that consumer initially tried to connect with IP
> address 10.0.2.15. Then suddenly it created SaslClient with a hostname:
> {code:java}
> [2019-06-18 06:23:36,486] INFO Kafka commitId: 00d486623990ed9d
> (org.apache.kafka.common.utils.AppInfoParser)
> [2019-06-18 06:23:36,487] DEBUG [Consumer
> clientId=KafkaStore-reader-_schemas, groupId=schema-registry-10.0.2.15-18081]
> Kafka consumer initialized (org.apache.kafka.clients.consumer.KafkaConsumer)
> [2019-06-18 06:23:36,505] DEBUG [Consumer
> clientId=KafkaStore-reader-_schemas, groupId=schema-registry-10.0.2.15-18081]
> Initiating connection to node 10.0.2.15:19094 (id: -1 rack: null) using
> address /10.0.2.15 (org.apache.kafka.clients.NetworkClient)
> [2019-06-18 06:23:36,512] DEBUG Set SASL client state to
> SEND_APIVERSIONS_REQUEST
> (org.apache.kafka.common.security.authenticator.SaslClientAuthenticator)
> [2019-06-18 06:23:36,515] DEBUG Creating SaslClient:
> client=null;service=kafka;serviceHostname=quickstart.confluent.io;mechs=[PLAIN]
> (org.apache.kafka.common.security.authenticator.SaslClientAuthenticator)
> {code}
> Thanks
> Badai
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