Numan,

 

Earlier I had send an e-mail with the following question that you responded to. 
 I maybe should have asked if the pipeline would redirect the DNS request to 
another DNS server to OVN.

 

1.       If OVN can't answer a DNS request, does the pipeline forward it on the 
another DNS server?  How is that server address set?  Though the DHCP options?

 

Yes. If OVN can't anwer it resumes the packet pipeline. So if there are any 
other DNS servers, they should get the packet.

I was looking at the flows in my OVN setup configured for DNS, and I don't see 
how the DNS request is redirected to a server external to OVN.

 

  table=16(ls_in_dns_lookup   ), priority=100  , match=(udp.dst == 53), 
action=(reg0[4] = dns_lookup(); next;)

  table=16(ls_in_dns_lookup   ), priority=0    , match=(1), action=(next;)

  table=17(ls_in_dns_response ), priority=100  , match=(udp.dst == 53 && 
reg0[4]), action=(eth.dst <-> eth.src; ip6.src <-> ip6.dst; udp.dst = udp.src; 
udp.src = 53; outport = inport; flags.loopback = 1; output;)

  table=17(ls_in_dns_response ), priority=100  , match=(udp.dst == 53 && 
reg0[4]), action=(eth.dst <-> eth.src; ip4.src <-> ip4.dst; udp.dst = udp.src; 
udp.src = 53; outport = inport; flags.loopback = 1; output;)

  table=17(ls_in_dns_response ), priority=0    , match=(1), action=(next;)

 

Based on these flows it looks like all udp.dst requests on port 53 are sent to 
dns_lookup.  If dns_lookup resolves the request it send the reply (either IPV4 
or IPV6).  If not, it proceeds to table 18, and I think eventually the request 
gets dropped.  Is there some later flow I should be looking for that would 
redirect the request to another DNS server (or is there something I'm missing 
in dns_lookup that does the redirect)?  If so, how does OVN/OVS know the ip 
address of that server?

 

John Lang

w (303) 272-5457

c (970) 231-3724

 
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