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Imagine there are two zones in one network, zone A and Zone B. host1 and host2 are both in zone A.

host1 is the dns authoritative server for zone A and host2 is the dns authoritative server for zone B. host1 is configured as the dns slave server for zone B and the zone transfer finishes without errors. host2 goes down. How do other hosts in zone B find host1 so they can send the DNS queries?

I tried to capture with Wireshark but couldn't understand how it happens. Do dns slave servers announce by broadcast they are the slave servers?

Edit: I made a new simulation and captures. I noticed a series of MDNS packets with source in the slave. Does the slave broadcast he is the slave after receiving the zone transfer?

znaya
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1 Answers1

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From the point of view of someone doing a recursing lookup, there is no such thing as a "slave server". There are servers that can provide authoritative responses for a domain, and servers who cannot. The master/slave distinction only exists from the point of view of those administering a domain.

So the answer to your question is "Because it's listed (with an NS record) in the zone's delegation information as a name server". If you do an NS lookup for a zone, you get a list of servers. All of those are authoritative servers for the zone. It may be that one is considered, by the people owning the zone, as a master and the rest as slaves, but for you looking in from the outside that distinction does not exist.

mDNS is a totally separate thing, with its own separate software, that happens to share some protocol stuff with DNS. It has absolutely nothing to do with finding name servers for zones. mDNS doesn't even have the concept "zone".

Calle Dybedahl
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  • I understand that from outside it is just another server. What I can't understand is how that information propagates after that server receives the zone transfer... – znaya Dec 14 '15 at 11:07
  • I thought the mDNS packets might be a way of that server to announce he is an authorative server for the zone. – znaya Dec 14 '15 at 12:48
  • No server ever announces that it is a server. Servers are pointed out by administrators adding NS records at the appropriate places, so a recursive resolver can follow pointers down from the root servers until it finds what it's looking for. – Calle Dybedahl Dec 14 '15 at 14:07
  • I see... In the named.conf file. But shouldn't that information, at least, be propagated to the root server? – znaya Dec 14 '15 at 14:26