Mar 27, 2026 - For details about updated CVE-2025-53521 (BIG-IP APM vulnerability), refer to K000156741.

Forum Discussion

AhmedSaied_2402's avatar
AhmedSaied_2402
Icon for Altostratus rankAltostratus
Jan 20, 2019

BIG IP DNS MX

Hello,   In intelligent DNS resolution we can use wide IPs and iRules   example to resolve type A when can use wide IP type A and iRule as below   when DNS_request { host 10.10.10.10 }  ...
application delivery
big-ip
BIG-IP DNS
DNS
irule
mx
Kai_Wilke's avatar
Kai_Wilke
Icon for MVP rankMVP
Jan 21, 2019

Hi Ahmed,

a DNS response to an MX query contain just a FQDN value, so you don't need to care about wide IPs.

Check the iRule sample below to get an overview how MX DNS responses can be crafted... 

when DNS_REQUEST {

    if { ( [string tolower [DNS::question type]] eq "mx")
     and ( [string tolower [DNS::question name]] eq "domain.de" ) } then {

         Defining DNS answers for the requested MX records (Question Name = Domain Name, ttl = 600, class = IN, type = MX, data = priority FQDN) 

        DNS::answer insert [DNS::rr "domain.de 600 IN MX 100 mx1.domain.de"] 
        DNS::answer insert [DNS::rr "domain.de 600 IN MX  50 mx2.domain.de"] 

         Changing "Authorative Answer" DNS header to true.

        DNS::header aa 1 

         Sending the DNS response

        DNS::return 
    }

}

Note: After the DNS response has been received by the MTA, it will perform an additional A and/or AAAA record lookups for the received FQDNs. This is where the wide IP comes into play...

Cheers, Kai