Source NAT for specific servers in a rule

Question

Hello,
I am trying to achieve source NATing on the CSS and want to confirm if below configuration is good.
VIP address: 61.61.61.61
Services: 10.1.1.1, 10.1.1.2, 20.1.1.1 and 20.1.1.2
Front-end circuit IP: 61.61.61.1 (Same subnet as 61.61.61.61)
Back-end circuit: 10.1.1.10 (Same subnet as 10.1.1.1 or .2)
service AAAA
ip address 10.1.1.1
active
service BBBB
ip address 10.1.1.2
active
service XXXX
ip address 20.1.1.1
active
service YYYY
ip address 20.1.1.2
active
owner Gateway
content Gateway1
vip address 61.61.61.61
add service 10.1.1.1
add service 10.1.1.2
add service 20.1.1.2
add service 20.1.1.1
active
As the two servers 20.1.1.1 and 20.1.1.2 are not in the same subnet, we configured the below to source NAT specifically to these two servers.
group Gateway
vip address 61.61.61.61
add destination service 20.1.1.1
add destination service 20.1.1.2
active
In the past this configuration didn't work. We are going to try it again. Is there anything missing and what else should we check to get it to work.
Appreciate any help.

Answer 1

Using 'add destination service' in the group rule NATs the original client IP as the VIP (in your case), and ensures that return traffic from the remote 20.x.x.x servers flows back to the CSS and then to the client instead of directly to the client (which would reject the traffic). There's no need to worry about any kind of load balancing loop being created. The downside to implementing this is that your servers will see all traffic as originating from the VIP and not the unique client IPs, and since the CSS doesn't support the x-forwarded-for header you're kinda stuck with that side effect.
Also, it's my understanding that the group rule must match the content rule in terms of VIP address and services within it to be effective. You would need to change your group rule to the following for it to work:
FROM:
group Gateway
  vip address 61.61.61.61
  add destination service 20.1.1.1
  add destination service 20.1.1.2
  active
TO:
group Gateway
  vip address 61.61.61.61
  add destination service 10.1.1.1
  add destination service 10.1.1.2
  add destination service 20.1.1.1
  add destination service 20.1.1.2
  active
Good luck!
James