Shulou(Shulou.com)06/01 Report--

Dnstracer

Summary: a command line tool for querying domain names corresponding to IP addresses and viewing DNS query packets; you can specify DNS servers, do not support batch queries, and send non-recursive domain name requests.

Syntax: dnstracer [options] [host]

-c: disable local caching (enabled by default)

-C: enable negative caching (disabled by default)

-o: enable summary of returned results (disabled by default,-o corresponds to-v,-o displays brief information about query results,-v displays details of query results)

-Q: specifies the type of query record. The default is A record.

-r: specify the number of retries. Default is 3.

-s: use this server as the initial request server (local DNS server is used by default). If specified, A.ROOT-SERVERS.NET will be used (A.ROOT-SERVERS.NET is one of 13 primary DNS servers in the world)

-t: sets the waiting time for each query

-v: detailed output (query results are not displayed by default, only whether records are found on the NS server)

-S: use this IP address as the source IP address of the packet

-4: do not query IPv6 server

Question and answer

What is a non-recursive domain name request?

Suppose host An is a machine; host B is a NS server, and host C is a NS server on the upper layer of B to query B for the IP address of www.google.com, but there is no corresponding record on B. at this time: if B makes a query to NS server C and returns the result to A, it is a recursive query; if B returns the address of NS server C to A, it is a non-recursive query.

What is local caching?

DNS local cache is a strategy to speed up site access. The windows system will save the domain name and the corresponding IP information in the system after accessing a domain name, which is convenient for quick access. It has not been thoroughly understood under linux. Windows view local cache: ipconfig / displaydnswindows requests this cache: ipconfig / flushdns starts local cache to improve the speed of the tool.

What is negative caching?

I took a big look, isn't this a negative cache? After a search, I found that there is no negative cache at all. Negative caching refers to the NS server to request a domain name, if the NS server cannot resolve it, it will store a cache record of negative caching in the local cache, in order to relieve the pressure on the NS server. For this tool, starting negative caching will reduce the time it takes for a domain name to explode, but it will not query the same domain name for multiple times.

Actual combat one:

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