[Dnsmasq-discuss] Is there an "all-servers" parameter for downstream servers?

[Simon Kelley]

Alberto Cuesta-Canada wrote:
> Hi all,
>  
> Is there an "all-servers" parameter for downstream servers?

There is an --all-servers configuration, but it only applies to upstream
servers which don't have a domain. This is an oversight: I don't think a
system which has more than one server for particular domains was
envisaged. This flag is not linked to a particular set of servers, so
setting it would cause the "all servers" behaviour to apply to the
"domainless" servers too. This isn't necessarily good.

As you noticed, the behaviour of servers-with-domains is different to
domainless servers. dnsmasq remembers which domainless server it used
last and continues to use that whilst is can, for domains-with-servers,
it always starts with the same server.

I can see three possible solutions.

1) Make --all-servers apply to servers-with-domains as well as
domainless ones.
2) Provide all-servers behaviour for servers-with-domains automatically
without having to set --all-servers.
3) Provide the complete remember-last-server for functionality for
servers-with-domains.


I think I prefer 2)


Simon.

>  
> I have a configuration with three DNS domains, each one served by two
> dnsmasq servers (complete description at the end).
>  
> I'm trying to set up a redundant structure, with cron jobs that ensure
> that both DNS servers for each domain are identical, so if one fails,
> the other will serve the requests. All the machines under my control
> repeat the query in rapid sucession if it doesn't come immediately
> answered, and the DNS servers seem to understand that so the behaviour
> is that any query from a machine in my domain reaches all dns servers in
> the network and it is always answered, regardless of which machines are
> down. For the size of my systems this is fine, it doesn't matter if it
> is unefficient.
>  
> The problem I have is that the corporate servers don't work that way. We
> have three of them, and when a machine outside my domains makes a query,
> all of them are queried and route to one of my main
> servers. Unfortunately they always ask to the first one, and never
> repeat the query. The round-robin protocol seems to reset for each
> query, so my main servers only ask the primary servers downstream, fail,
> and the corporate servers return (and cache) a failure, thus rendering
> my failover structure useless for other domains.
>  
> This could be solved modifying the configuration on the corporate server
> (politics!), or instructing the my main dns servers to always route
> queries to all servers downstream, and to serve the first result coming
> up. It's the same as using "all-servers", but downstream.
>  
> Here is a small diagram (use monospace to see it):
>  
>                         CORPORATE    172.30.0.1    (corporate.local)
>                                      172.30.0.2
>                                      172.30.1.1
>                                          ||
>                                          || *.mydomain.local
>                                          ||
>                            MAIN    192.168.0.250    (main.mydomain.local)
>                                    192.168.0.251
>                                     ||       ||
>                 sub1.mydomain.local ||       || sub2.mydomain.local
>                                     ||       ||
>                   SUB1    192.168.1.250     192.168.2.250    SUB2
>                           192.168.1.251     192.168.2.251
>  
> server=/sub1.mydomain.local/192.168.1.250
> server=/sub1.mydomain.local/192.168.1.251
> server=/sub2.mydomain.local/192.168.2.250
> server=/sub2.mydomain.local/192.168.2.251
>   
> Many thanks,
>  
> *Alberto Cuesta-Canada*
> GaaS Team Lead
> Excelian Ltd.
> +44 (0) 7942633361
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