Implementing Client Subnet DNS Requests
Problem this snippet solves:
Update 2018-10-23: As of BIG-IP DNS 14.0 there is now a checkbox feature for edns-client-subnet. Please see: Using Client Subnet in DNS Requests. The following is still useful if you want to customize your responses.
Original post:
Using an iRule and edns-client-subnet (ECS) we can improve the accuracy of F5 GTM’s topology load balancing.
- DevCentral Article: Implementing Client Subnet DNS Requests
How to use this snippet:
There are two different iRules. One is an LTM iRule and the second is a GTM iRule. These should be deployed separately.
Code :
#
# LTM iRule
#
# comply with draft to respond with ECS
when DNS_REQUEST {
if { [DNS::edns0 exists] &! [catch { DNS::edns0 subnet address }] } {
set ecs_address [DNS::edns0 subnet address]
set ecs_source [DNS::edns0 subnet source]
set ecs_scope [DNS::edns0 subnet scope]
log local0. "Received EDNS request from [IP::client_addr]:$ecs_address/$ecs_source/$ecs_scope"
}
}
when DNS_RESPONSE {
if { [info exists ecs_address] } {
DNS::edns0 subnet address $ecs_address
DNS::edns0 subnet source $ecs_source
#DNS::edns0 subnet scope $ecs_scope
# hardcode the desired scope to be /24, not sure this is OK
DNS::edns0 subnet scope 24
}
}
#
# GTM iRule
#
when DNS_REQUEST {
set ldns [IP::client_addr]
log local0. "LDNS LOC: $ldns [whereis $ldns]"
if { [DNS::edns0 exists] &! [catch { DNS::edns0 subnet address }] } {
set gtm_ecs_address [DNS::edns0 subnet address]
set gtm_ecs_source [DNS::edns0 subnet source]
set gtm_ecs_scope [DNS::edns0 subnet scope]
set ldns $gtm_ecs_address
log local0. "ECS LOC: $gtm_ecs_address [whereis $ldns]"
}
set loc [whereis $ldns]
if { $loc contains "NA" } {
log local0. "NA"
}
elseif { $loc contains "AS" } {
log local0. "Asia"
}
elseif { $loc contains "EU" } {
log local0. "Europe"
} else {
log local0. "All other"
}
}Tested this on version:
11.6Published Jun 16, 2015
Version 1.0
