F5 is upgrading its customer support chat feature on My.F5.com. Chat support will be unavailable from 6am-10am PST on 1/20/26. Refer to K000159584 for details.

Using Client Subnet in DNS Requests

BIG-IP DNS 14.0 now supports edns-client-subnet (ECS) for both responding to client requests (GSLB) or forwarding client requests (screening). The following is a quick start on using this feature. ...
Published Sep 14, 2018
Version 1.0
application delivery
BIG-IP DNS
dragonflymr's avatar
dragonflymr
Icon for Cirrostratus rankCirrostratus
Jan 23, 2019

Hi,

 

Great article!

 

I have still some small doubts how ECS and Persistence works. Based on previous posts from Robin (thanks a lot Robin for sharing) it seems to work like that (for WideIP):

 

  1. Persistence enabled at WideIP
  2. Prefer Client Subnet checked

Result: Source IP of DNS server sending query is disregarded, persistence record is created based on Client Subnet in the query

 

  1. Persistence enabled at WideIP
  2. Prefer Client Subnet not checked

Result: Client subnet info in request is ignored, persistence record is based on IP of DNS server sending query.

 

Am I right with above?

 

Is that schema valid for any other LB used? For example RR, so if there is not persistence record (based on client subnet in request) LB is performed. If persistence record exists then LB is ignored and same IP is returned.

 

I am as well curious if anyone succeeded with enabling ECS on any version of Windows Srv?

 

Piotr