[-46apsQR ] [-b expression ] [-i address ] [-f filter ] [-r interval ] [device ] [savefile ]
is a small tool to listen on device or to parse the file savefile and collect and print statistics on the local network's DNS traffic. You must have read access to /dev/bpf*
The options are as follows:
For example, with -l 2 (the default), will keep two tables: one with top-level domain names, and another with second-level domain names. Increasing the level provides more details, but also requires more memory and CPU.
The "unknown-tlds" filter includes only queries for TLDs that are bogus. Useful for identifying hosts/servers that leak queries for things like "localhost" or "workgroup."
The "A-for-A" filter includes only A queries for names that are already IP addresses. Certain Microsoft Windows DNS servers have a known bug that forward these queries.
The "rfc1918-ptr" filter includes only PTR queries for addresses in RFC1918 space. These should never leak from inside an organization.
The "refused" filter, when used with the -R option, tells to count only replies with rcode REFUSED.
The "qtype-any" filter tells to count only message of type ANY.
While running, the following options are available to alter the display:
If stdout is not a tty, runs in non-interactive mode. In this case, you must supply a savefile for reading, instead of capturing live packets. After reading the entire savefile, prints the top 50 entries for each table.
By default examines only query messages and ignores replies. In this case the response code table is meaningless and will likely show 100% "Noerror."
If you supply (only) the -R command line option, examines replies and ignores queries. This allows you to see meaningful response code values, as well as all the other tables. In this case all the query attributes (such as type and name) are taken from the Question section of the reply.
Note, however, that it is common for a stream of DNS messages to contain more queries than replies. This could happen, for example, if the server is too busy to respond to every single query, or if the server is designed to ignore malformed query messages. Therefore, you might want to examine both queries and replies by giving both -R and -Q command line options. In this case, only the response code counts are taken from the replies and all other attributes are taken from the queries.
Does not support TCP at this time.