active/active LTM deployment on different subnet

HI Nitass,

 

I believe what you are asking is possible. I have lab tested something similar several years ago where I wanted to avoid using a GTM or like service and found that it would increase complexity across the board and it was not fully automated - some manual manipulation was required.

 

 

My lab setup was the following

 

 

Datacenter A

 

Circuit A

 

VIP A (Active)

 

VIP B (Dormant)

 

Servers A

 

 

Datacenter B

 

Circuit B

 

VIP B (Active)

 

VIP A (Dormant)

 

Server B

 

 

I ran BGP peering between Datacenter A and B (which used 2 different ISPs). I created VIP A and B on Datacenter A and the same in Datacenter B. However, only the VIPs that were being advertised in their respective ISPs were ever responding. I then created a route pools which custom health checked IP addresses on the upstream router (checking for latency and ICMP). Since ADCs in both data centers were connected to switch routers (Cisco 6509s), I created secondary addresses on the subnets (VIP A and B).

 

 

This worked well in the lab, however, I found one large issue. Because BGP was being used, fail over could take anywhere between 30 seconds to 5 minutes depending on your ISPs defaults. I even looked into beefing up BGP with PfR(Performance Routing). However, this required the ISP to support it and not all ISPs offer this type of configuration. I even looked at lowering the BGP timers - again the ISP had to support it on their end which is highly unlikely when you deviate from the known standards.

 

 

In conclusion, I decided against this approach because it simply could not guarantee consistent failover within a reasonable amount of time as well as the complexity in maintaining this configuration. Thus we decide that the GTM would provide the best solution overall.

 

 

 

I hope this helps

 

Bhattman