Difference betwen failed request with addit RR and successfull without.

joseangel.martinezdelavara at telefonica.es joseangel.martinezdelavara at telefonica.es
Tue Feb 14 14:03:17 UTC 2006

Hi, there.

I am having a weird problem here. It looks like my DNS server manages to
resolve DNS queries to the internet name servers on fouth attempt. Sniffing
on the local interface I can see three unreplied requests sent to three
different nameservers then a successful one to another one.

It would not be so rare if those first NS were dead, but they were not
since a direct dig to them actually worked (and works).

The only difference among failed and succesfull requests is that failed
requests have a few more flags active, that is:
- Non-authenticated data OK (meaning non-authenticated data is acceptable)
- Additional RRs flag (so there are additional records)

The additional record present (according to ethereal decode of an snoop run
on my dns server) is a type OPT class unknown with the following fields:
- name: <root>
- type: EDNS0 option
- UDP payload size: 2048
- Higher bist in extended RCODE: 0x0
- EDNS version: 0
- Z: 0x0
- Data length: 0
- Data:

It cannot be that the response from the servers arrives late because I run
snoop for quite some time after the test was finished. So, why are requests
without those flasgs active successfull and the others are not.

BTW, those flags were not active on successfull direct requests with dig
agains external dns servers (bypassing mine).

I am running BIND 9.2.3 on this piece of hardware/software:
root at mvicprb01b16 # uname -a
SunOS mvicprb01b16 5.9 Generic_118558-10 sun4u sparc SUNW,Serverblade1

I can provide with the snoop file to read with ethereal if requested, but I
do not feel I shoudl be posting a binary file here. :)

Thanks a lot

Jose Angel Martinez
TME - Direccion de servicios de valor añadido
joseangel.martinezdelavara at telefonica.es


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