[MaraDNS list] Fwd: MaraDNS doesn't respond to queries from the bind addr subnet

[Dave Owens]

Hi Sam,

I tried this with your lightweight DNS server, on a different machine (same
route), still no luck.  Testing a non-connected rfc1918 returns a response,
testing a connected rfc1918 address does not work.

An enhanced packet capture shows that when the reply for the 'special' A
record is sent to the router, the router replies with an
icmp-host-unreachable packet indicating the that the destination IP is
unreachable.... I must be hitting a bug or possibly hidden configuration in
the router OS.

Attached is a .pcapng file that illustrates the behavior... first request
succeeds, subsequent three requests fail.

Dave Owens
TeamUnify, LLC





On Fri, Jun 14, 2013 at 11:13 AM, Sam Trenholme <maradns at gmail.com> wrote:

> > Yesterday I ran captures both on our DNS node (it indeed sends the reply)
> > and on the other side of our edge router (no reply is seen).  Our colo
> > provider says they aren't doing any deep packet inspection around this...
>
> I want to know how this gets resolved--so I can add this information
> to the MaraDNS FAQ (which is horribly outdated and needs a serious
> revamp).  There is a small chance it’s a case of “MaraDNS makes a
> weird DNS packet which this route doesn’t like”. One way to normalize
> against that is to have another computer whose packets go through the
> same route use a different DNS server to send out the 192.168.50.141
> DNS reply.
>
> For example, here’s a DNS server I wrote a few years ago:
>
> $ cat > nanodns.c
> /*Placed in the public domain by Sam Trenholme*/
> #include <arpa/inet.h>
> #include <string.h>
> #include <stdint.h>
> #define Z struct sockaddr
> #define Y sizeof(d)
> int main(int a,char **b){uint32_t i;char q[512]
> ,p[17]="\xc0\f\0\x01\0\x01\0\0\0\0\0\x04";if(a>
> 1){struct sockaddr_in d;socklen_t f=511;bzero(&
> d,Y);a=socket(AF_INET,SOCK_DGRAM,0);*((uint32_t
> *)(p+12))=inet_addr(b[1]);d.sin_family=AF_INET;
> d.sin_port=htons(53);bind(a,(Z*)&d,Y);for(;;){i
> =recvfrom(a,q,255,0,(Z*)&d,&f);if(i>9&&q[2]>=0)
> {q[2]|=128;q[11]?q[3]|=4:1;q[7]++;memcpy(q+i,p,
> 16);sendto(a,q,i+16,0,(Z*)&d,Y);}}}return 0;}
> // Hit control-D to end this file here
> $ gcc -g -O nanodns nanodns.c
> $ su
> Password:
> # ./nanodns 192.168.50.141
>
> At this point, the machine is running a tiny little DNS server which
> will reply to all DNS queries with the IP 192.168.50.141.
>
> I have a more readable version of that DNS server here:
>
> http://samiam.org/software/microdns.html
>
> - Sam
>