[Bro] Questions about Bro's DNS Parser

daniela.miao at utoronto.ca daniela.miao at utoronto.ca
Sat Feb 6 21:29:13 PST 2010

Hi Vern,

Thanks for your time. I was actually running into the ip checksum  
errors before, but then I discovered the -C option.

The problem is, even with the -C option, some packets that have error  
codes such as "Server Failure" or "No Such Name Exists" are not being  
logged in the DNS log file. The log file only contains information  
regarding packets that had no errors. This confuses me, since it  
appears that dns-info.bro file contains information required for error  
code deciphering.

A closer look at the dns log file as given right now reveals that  
whenever there is a packet that contains an error, the parser simply  
stalls, and prints out the query as is, instead of deciphering the  
error code.

Any suggestions would be much appreciated, thank you very much,


Quoting Vern Paxson <vern at icir.org>:

>> Anyhow, I have attached a sample capture from the trace file, which
>> contains DNS packets with returned errors (some response packets). I
>> also took a look at dns.bro, if I'm not mistaken the parser does not
>> have any error code interpreting feature, it seems all to be group
>> into Weird::WEIRD_FILE.
> Do you mean errors based on the analyzer's parsing failing, or errors
> indicated via the DNS protocol?  The latter are logged in the DNS log file.
> For the former, when I run on the file all I get in the weird file is IP
> checksums.  If I use -C to ignore these then I get a bunch of DNS log file
> output that seems reasonable, so I'm not immediately seeing the problem.
> 		Vern

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