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While configuring one of Cisco's routers and reading documentation I've found an interesting feature: ip domain round-robin.

Documentation says, that this options makes dns server rotate entries within TTL. I have enabled this feature under the impression that this will give out rotated entries upon every request. But that is not the case, and later I've found a note on this feature, that clarifies that it does so only for internal lookups. And indeed, issuing ping on a console does rotate entries and clients receive rotated entries after that.

With it being enabled only for an internal lookup, it must have a rather limited usefullnes. What is the purpose of this feature then? Is there any option to enable this for all clients?

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With it being enabled only for an internal lookup, it must have a rather limited usefulness. What is the purpose of this feature then?

The idea is that when the router (i.e., using the management plane) does a DNS query, it will rotate the server used, presumably for redundancy. Typically, Cisco will add features if requested by big clients. I imagine this falls into that category.

Is there any option to enable this for all clients?

No. This is only for the router management. A router is not a name server.

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  • (At least some) Cisco routers can act as a DNS resolver and serving some local data but this is not necessarily a good idea. I tried this once and now my name can be found in a Cisco advisory. ;-) Haven't tried it again. – Jens Link Jul 8 at 12:45
  • Thanks for the answer and for reminding me that a router is not a name server. – PF4Public Jul 8 at 23:25
  • "it will rotate the server used" this does not seem to correspond to documentation stated as "that this options makes dns server rotate entries within TTL" (rotate entries within TTL). In DNS, round robin is related to the fact that a given query can get multiple replies (example: a name resolving to multiple A records), and hence round robin means the order of the records is changed at each query (there is no internal order in the DNS, records are sets, not lists). Phrasing in doc is a little strange: since DNSSEC and a little before, all records for same name+type have same TTL anyway. – Patrick Mevzek Jul 9 at 17:24

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