NAME¶
dnstop —
displays various tables of DNS
traffic on your network
SYNOPSIS¶
dnstop |
[-46apsQR]
[-b
expression]
[-i
address]
[-f
filter]
[-r
interval]
[device]
[savefile] |
DESCRIPTION¶
dnstop 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*.
COMMAND LINE OPTIONS¶
The options are as follows:
- -4
- count only messages with IPv4 addresses
- -6
- count only messages with IPv6 addresses
- -Q
- count only DNS query messages
- -R
- count only DNS reply messages
- -a
- anonymize addresses
- -b
expression
- BPF filter expression
(default: udp port 53)
- -i
address
- ignore select addresses
- -p
- Do not put the interface into promiscuous mode.
- -r
- Redraw interval (seconds).
- -l
level
- keep counts on names up to level domain
name levels.
For example, with -l 2 (the default), dnstop 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.
- -f
- input filter name
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 dnstop to count only replies with rcode
REFUSED.
The "qtype-any" filter tells dnstop to count
only message of type ANY.
- -n
name
- Only count messages within the domain
name
- -P
- Print "progress" messages on stderr when in
non-interactive mode.
- -B
buckets
- Use buckets hash table buckets.
- -X
- Do not tabulate the sources + query name counters. This can
significantly reduce memory usage on busy servers and large
savefiles.
- savefile
- a captured network trace in pcap
format
- device
- ethernet device (ie fxp0)
RUN TIME OPTIONS¶
While running, the following options are available to alter the display:
- s
- display the source address table
- d
- display the destination address table
- t
- display the breakdown of query types seen
- r
- display the breakdown of response codes seen
- o
- display the breakdown of opcodes seen
- 1
- show 1st level query names
- 2
- show 2nd level query names
- 3
- show 3rd level query names
- 4
- show 4th level query names
- 5
- show 5th level query names
- 6
- show 6th level query names
- 7
- show 7th level query names
- 8
- show 8th level query names
- 9
- show 9th level query names
- !
- show sources + 1st level query names
- @
- show sources + 2nd level query names
- #
- show sources + 3rd level query names
- $
- show sources + 4th level query names
- %
- show sources + 5th level query names
- ^
- show sources + 6th level query names
- &
- show sources + 7th level query names
- *
- show sources + 8th level query names
(
- show sources + 9th level query names
- ^R
- reset the counters
- ^X
- exit the program
- space
- redraw
- ?
- help
NON-INTERACTIVE MODE¶
If stdout is not a tty,
dnstop 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,
dnstop
prints the top 50 entries for each table.
HOW MESSAGES ARE COUNTED¶
By default
dnstop 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,
dnstop 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.
AUTHORS¶
- Duane Wessels
(wessels@measurement-factory.com)
-
- Mark Foster
(mark@foster.cc)
-
- Jose Nazario
(jose@monkey.org)
-
- Sam Norris
<@ChangeIP.com>
-
- Max Horn
<@quendi.de>
-
- John Morrissey
<jwm@horde.net>
-
- Florian Forster
<octo@verplant.org>
-
- Dave Plonka
<plonka@cs.wisc.edu>
-
- http://dnstop.measurement-factory.com/
-
BUGS¶
Does not support TCP at this time.