ITD (Intelligent Traffic Director) L4 load balance

[Nadav Katz]

Hello,

I have read about the ITD and didn't understand something about the L4 load balancing use-case.

Cisco notes that if you deploy L4 load balance with ITD, the backend server must be configured with the VIP on a loopback interface (AKA. DSR or Local Triangulation).

This is make sense and widely deployed, but, Cisco notes that the ITS with L4 load balance also doing destination NAT.

I didn't understand it, Why should we configure destination NAT if the server holds the VIP IP on a loopback interface?

The meaning of DSR\Local Triangulation is that the server will reply directed to the client with the VIP as a source IP (it can do it if it initiate the connection from the loopback\VIP IP), so the destination NAT in not just unnecessary, its make a problem, because now the server will initiate the connection from the real server IP and the client will send a TCP RST to the SYN, ACK (caused by mismatch IP related to the TCP SYN destination IP sent by the client).

Can someone explain me what actual occur?

Thanks a lot,

Nadav

[Nadav Katz]

Nevermind.

Found the answer on cisco's documentation:

http://www.cisco.com/c/en/us/support/docs/routers/7000-series-routers/118950-config-nexus-00.html#anc5

They wrote the following - "The IP address is not translated by ITD. The traffic that egresses the Nexus 7000 towards the nodes has a 192.168.30.1 destination address and retains the original source IP address".

So, just for make it clear, when configuring ITD, there is no need for detinatination NAT and DSR\Local Triangulation is deployed.

Thanks,

Nadav.