问题复现
近日针对某一客户需求开发了一个需要使用Kafka的功能，功能是什么暂且不论，在本地虚机的Kafka连接一切正常遂放到测试服务器上验证功能，以下是监听topic成功和警告报错：
2023-05-09 10:22:23 [localhost-startStop-1] INFO org.apache.kafka.clients.consumer.ConsumerConfig - ConsumerConfig values:
allow.auto.create.topics = true
auto.commit.interval.ms = 5000
auto.offset.reset = earliest
bootstrap.servers = [10.39.48.113:9092]
check.crcs = true
client.dns.lookup = use_all_dns_ips
client.id = consumer-enn-jiuqi-1
client.rack =
connections.max.idle.ms = 540000
default.api.timeout.ms = 60000
enable.auto.commit = false
exclude.internal.topics = true
fetch.max.bytes = 52428800
fetch.max.wait.ms = 500
fetch.min.bytes = 1
group.id = enn-jiuqi
group.instance.id = null
heartbeat.interval.ms = 3000
interceptor.classes = []
internal.leave.group.on.close = true
internal.throw.on.fetch.stable.offset.unsupported = false
isolation.level = read_uncommitted
key.deserializer = class org.apache.kafka.common.serialization.StringDeserializer
max.partition.fetch.bytes = 1048576
max.poll.interval.ms = 300000
max.poll.records = 500
metadata.max.age.ms = 300000
metric.reporters = []
metrics.num.samples = 2
metrics.recording.level = INFO
metrics.sample.window.ms = 30000
partition.assignment.strategy = [class org.apache.kafka.clients.consumer.RangeAssignor, class org.apache.kafka.clients.consumer.CooperativeStickyAssignor]
receive.buffer.bytes = 65536
reconnect.backoff.max.ms = 1000
reconnect.backoff.ms = 50
request.timeout.ms = 30000
retry.backoff.ms = 100
sasl.client.callback.handler.class = null
sasl.jaas.config = null
sasl.kerberos.kinit.cmd = /usr/bin/kinit
sasl.kerberos.min.time.before.relogin = 60000
sasl.kerberos.service.name = null
sasl.kerberos.ticket.renew.jitter = 0.05
sasl.kerberos.ticket.renew.window.factor = 0.8
sasl.login.callback.handler.class = null
sasl.login.class = null
sasl.login.refresh.buffer.seconds = 300
sasl.login.refresh.min.period.seconds = 60
sasl.login.refresh.window.factor = 0.8
sasl.login.refresh.window.jitter = 0.05
sasl.mechanism = GSSAPI
security.protocol = PLAINTEXT
security.providers = null
send.buffer.bytes = 131072
session.timeout.ms = 45000
socket.connection.setup.timeout.max.ms = 30000
socket.connection.setup.timeout.ms = 10000
ssl.cipher.suites = null
ssl.enabled.protocols = [TLSv1.2]
ssl.endpoint.identification.algorithm = https
ssl.engine.factory.class = null
ssl.key.password = null
ssl.keymanager.algorithm = SunX509
ssl.keystore.certificate.chain = null
ssl.keystore.key = null
ssl.keystore.location = null
ssl.keystore.password = null
ssl.keystore.type = JKS
ssl.protocol = TLSv1.2
ssl.provider = null
ssl.secure.random.implementation = null
ssl.trustmanager.algorithm = PKIX
ssl.truststore.certificates = null
ssl.truststore.location = null
ssl.truststore.password = null
ssl.truststore.type = JKS
value.deserializer = class org.apache.kafka.common.serialization.StringDeserializer
2023-05-09 10:22:23 [localhost-startStop-1] INFO org.apache.kafka.common.utils.AppInfoParser - Kafka version: 3.0.1
2023-05-09 10:22:23 [localhost-startStop-1] INFO org.apache.kafka.common.utils.AppInfoParser - Kafka commitId: 8e30984f43e64d8b
2023-05-09 10:22:23 [localhost-startStop-1] INFO org.apache.kafka.common.utils.AppInfoParser - Kafka startTimeMs: 1683598943212
2023-05-09 10:22:23 [localhost-startStop-1] INFO org.apache.kafka.clients.consumer.KafkaConsumer - [Consumer clientId=consumer-test-1, groupId=test-group] Subscribed to topic(s): sync_user
2023-05-09 10:23:50 [org.springframework.kafka.KafkaListenerEndpointContainer#0-0-C-1] WARN org.apache.kafka.clients.NetworkClient - [Consumer clientId=consumer-test-1, groupId=test-group] Bootstrap broker 10.39.48.113:9092 (id: -1 rack: null) disconnected
可以注意到日志最后有1条警告，其实我只放了一条，这个信息在日志里多滴很。
分析问题
客户对接方发送了一条消息问我们消费到没，我一查日志，满屏是WARN提示 Bootstrap broker 10.39.48.113:9092 (id: -1 rack: null) disconnected，真是小刀拉屁股——开了眼。
打开Google Bard机器人问问这是啥原因导致的：
可能是网络原因导致的，查了下其他博客说也有可能是开启了某种认证机制导致的。
通过ping发现能ping通broker，但是通过telnet却无法连接了，也就是说：这台测试服务器与kafka broker间的网络被限制为可以ping但不能访问broker的端口号！
解决办法
查看了下测试服务器的iptables链没发现问题，自己通过tcpdump抓包用wireshark分析发现只有SYN包没响应，找到客户网络工程师定位到是公司的网络策略限制了。至此问题解决，希望能给读者一个思路。