External passthrough Network Load Balancer - tcpdump destination IP

Google Cloud Compute Infrastructure
1

I have a setup with an ‘External passthrough Network Load Balancer’ , instance group, and a compute instace with public IP attached.

If accesing the compute instance via the attached IP, in tcpdump the destination IP is the internal one:

5.x.y.z.52544 > 10.128.0.9.80

If accessing via the loadbalancer , the destination IP seen with tcpdump on the server is the loadbalancers external IP:

5.x.y.z.52858 > 34.171.b.c.80

Is there any setting/option to have on the server same behavior with or without loadbalancer?

Thanks.

2

Hi @czke ,

Welcome to Google Cloud Community!

You may want to check the Proxy Network Load Balancer and enable the Proxy Protocol. This protocol passes the original destination IP and other connection details to the server, even if traffic is routed through a Load Balancer. This will pass the original destination IP in the request headers. You would then need to configure your server to interpret the Proxy Protocol header to get the correct destination IP.

Proxy Network Load Balancers are intended for TCP traffic only, with or without SSL. For HTTP(S) traffic, we recommend that you use an Application Load Balancer instead.

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