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Forum Discussion

jayanthi_41101's avatar
jayanthi_41101
Icon for Nimbostratus rankNimbostratus
Jun 12, 2017

Use DNS server list for DNS resolution through F5 LTM irule

We already use DNS resolution using one specific DNS server in RESOLV::lookup. I am trying to figure out a solution where i can use a list of DNS servers and not finding any resources for it.   C...
application delivery
LTM
tcastaing_23984's avatar
tcastaing_23984
Icon for Nimbostratus rankNimbostratus
Dec 18, 2017

Here is a working solution that is choosing randomly a DNS server from the specified list.

 FQDN to resolve
set FQDN_TO_RESOLVE "www.example.com"

 DNS server list
set DNS_SERVER_LIST {1.1.1.1 2.2.2.2 3.3.3.3}

 Select a DNS server from the list
set SELECTED_DNS_SERVER "[lindex $DNS_SERVER_LIST [expr {int(rand()*[llength $DNS_SERVER_LIST])}]]"

 Perform the Lookup
set FQDN_RESOLVED_IP "[lindex [RESOLV::lookup @$SELECTED_DNS_SERVER -a $FQDN_TO_RESOLVE] 0]"