Plain vanilla is an adjective describing the simplest version of something, without any optional extras, by analogy with vanillaice cream, the default flavour.

1. Name servers host a domain’s DNS information in a text file called the zone file. They’re are also known as **Servers of
   Authority (SOAs)**
2. On Linux (and probably most Unix), there is no OS-level DNS caching unless nscd is installed and running. Even then, the DNS caching feature of nscd is disabled by default at least in Debian because it's broken. The practical upshot is that your linux system very very probably does not do any OS-level DNS caching.
3. An AAAA record is just like an A record, but for IPv6 IP addresses. A typical AAAA record looks like the following:

参考 https://www.linode.com/docs/networking/dns/dns-records-an-introduction

Memory Analyzer can currently work with three dump types:

1. IBM Portable Heap Dump (PHD): This proprietary IBM format contains
   only the type and size of each Java object in the process, and the
   relationships among the objects. This dump-file format is
   significantly smaller than the other formats and contains the least
   information. The data is usually sufficient, though, for diagnosing
   memory leaks and getting a basic understanding of the application's
   architecture and footprint.
2. HPROF binary dump: The HPROF binary format contains all the data
   present in the IBM PHD format as well as the primitive data held
   inside the Java objects, and the thread details. You can look at the
   values held in fields inside the objects and see which methods were
   being executed at the time the dump was taken. The additional
   primitive data makes HPROF dumps significantly larger than
   PHD-format dumps; they are approximately the same size as the used
   Java heap.
3. IBM system dumps: When the IBM Java runtime is being used, the
   native operating-system dump file — a core file on AIX® or Linux, a
   minidump on Windows®, or a SVC dump on z/OS®— can be loaded into
   Memory Analyzer. These dumps contain the entire memory image of the
   running application — all the information and data in the HPROF
   format, as well as all of the native-memory and thread information.
   This is the largest and most comprehensive dump-file format.

Both IBM dump types are available only with the Diagnostic Tool Framework for Java (DTFJ) plug-in installed

节选自: https://www.ibm.com/developerworks/library/j-memoryanalyzer/#table1

nc (netcat) - arbitrary TCP and UDP connections and listens
-words [-46DdhklnrStUuvz] [-i interval] [-p source_port] [-s source_ip_address] [-T ToS] [-w timeout] [-X proxy_protocol] [Xo -x proxy_address[: port]] [hostname] [port[s]]
nc -wz baidu.com

mtr - a network diagnostic tool

 mtr combines the functionality of the traceroute and ping programs in a single network diagnostic tool.

mtr -rw example.com

Th Java VisualVM automatically detects and connects to the Java Management Extensions (JMX) agents for Java applications that are running on JDK or that have been started with the correct system properties. For the tool to detect and connect to the agents on a remote machine, the jstatd daemon must be running on the remote machine, see The jstatd Daemon. If Java VisualVM cannot automatically discover and connect to JMX agents that are running in a target application, then the tool provides a means for you to explicitly create these connections.
官方文档 在这里
you can:

1. View a list of local and remote Java applications.
2. View application configuration and runtime environment. For each
   application, the tool shows basic runtime information: PID, host,
   main class, arguments passed to the process, JVM version, JDK home,
   JVM flags, JVM arguments, and system properties.
3. Enable and disable the creation of a heap dump when a specified
   application encounters an OutOfMemoryError exception.
4. Monitor application memory consumption, running threads, and loaded
   classes.
5. Trigger a garbage collection immediately.
6. Create a heap dump immediately. You can then view the heap dump in
   several views: summary, by class, by instance. You can also save the
   heap dump to your local file system.
7. Profile application performance or analyze memory allocation (for
   local applications only). You can also save the profiling data.
8. Create a thread dump (stack trace of the application's active
   threads) immediately. You can then view the thread dump.
9. Analyze core dumps (with Oracle Solaris and Linux operating
   systems).
10. Analyze applications offline, by taking application snapshots.