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Arnor_Arnason's avatar
Arnor_Arnason
Icon for Altostratus rankAltostratus
May 23, 2011

How to answer a DNS SRV request in a irule on GTM

Hi, I know how I could answer an A request directly with an host ip in an irule: when DNS_REQUEST { if { [IP::addr [IP::client_addr]/24 equals "10.10.10.0] } { use pool GTM_pool1 }...
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Kai_Wilke's avatar
Kai_Wilke
Icon for MVP rankMVP
Jan 19, 2016

Hi Aref,

you may try the syntax below to intercept and respond to a specific SRV DNS query. It will also set authority information and additional records for the resolved SRV records to speed up DNS resolution (if supported by the DNS client).

when DNS_REQUEST { 

    log local0. "\[DNS::question name\]: [DNS::question name], \[DNS::question class\]: [DNS::question class], \[DNS::question type\]: [DNS::question type]"

    set ttl 300
    if { [string tolower [DNS::question name]] starts_with "_ldap._tcp.dc._msdcs.domain.de" } then { 

        if { [DNS::question type] equals "SRV" } then {

             SOA information
            DNS::authority insert "domain.de. $ttl IN SOA server1.domain.de hostmaster.domain.de 1337 900 600 86400 3600"

             SRV response
            DNS::answer insert "[DNS::question name]. $ttl IN [DNS::question type] 1 0 389 server1.domain.de"
            DNS::answer insert "[DNS::question name]. $ttl IN [DNS::question type] 1 0 389 server2.domain.de"

             Additional records
            DNS::additional insert  "server1.domain.de. $ttl IN A 192.168.1.1"
            DNS::additional insert  "server2.domain.de. $ttl IN A 192.168.1.2"
            DNS::return

        }
    }
}

Note: The syntax can be used for v11.1+ LTM deployments.

Cheers, Kai