How to troubleshoot the traffic flow ?

Question

I have the following:
![Enter image description here](/media/postImages/original/IMph1Kqo97Qe6uze68DPaI8A)
I did this in a demo lab. It works. The demo created VPC and EC2 via cloudformation. I only configured TGW and both eth0 and eth1 Route table.
But when I configured everything manually, traffic flow was successful without via the service VPC, instead of via only TGW. But after I moved Client and Server attachments to service RT and reconfigured eth0 and eth1 based on the instruction. No traffic flows to eth0. 
Any way or tool can be used to identify which step is broken ?

thanks !!

Oleksii Bebych · Accepted Answer

> Reachability Analyzer is a configuration analysis tool that enables you to perform connectivity testing between a source resource and a destination resource in your virtual private clouds (VPCs). When the destination is reachable, Reachability Analyzer produces hop-by-hop details of the virtual network path between the source and the destination. When the destination is not reachable, Reachability Analyzer identifies the blocking component. For example, paths can be blocked by configuration issues in a security group, network ACL, route table, or load balancer.

https://docs.aws.amazon.com/vpc/latest/reachability/what-is-reachability-analyzer.html

gongya · Answer

thanks so much !!

How to troubleshoot the traffic flow ?

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