With VR + VNF + L2 Network, the VMs in L2 Network cannot be reached from the Internet (But the opposite is possible)

##### ISSUE TYPE

* Bug Report

##### COMPONENT NAME

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VR + VNF
~~~

##### CLOUDSTACK VERSION

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4.19.1
~~~

##### CONFIGURATION

Advanced Networking
VPC
VNF + L2 Network

##### OS / ENVIRONMENT

##### SUMMARY

We have 1 VPC and 1 L2 Network connected together with a VNF (PFsense) in between.

Results Summary:
- Test 1: From L2 VM (10.26.8.230) to VPC VM (10.26.1.250) - PASS
- Test 2: From VPC VM (10.26.1.250) to L2 VM (10.26.8.230) - FAILED
- Test 3: From L2 VM (10.26.8.230) to Private Gateway VM (10.88.5.82) - PASS
- Test 4: From Private Gateway VM (10.88.5.82) to L2 VM (10.26.8.230) - FAILED

Background:
We’ve allowed any on the VNF firewall rules as attached in the screenshot below:


Traffic is allowed any on 10.26.1.254 interface


Traffic is allowed any on 10.26.8.254

We then run some tests.

Test 1: From L2 VM (10.26.8.230) to VPC VM (10.26.1.250)

Results: Ping and traceroute test from 10.26.8.230 to 10.26.1.250 works as expected. (PASS)


Test 2: From VPC VM (10.26.1.250) to L2 VM (10.26.8.230)


Results: Ping and traceroute test from 10.26.1.250 to 10.26.8.230 is not possible (FAILED)


Test 3: From L2 VM (10.26.8.230) to Private Gateway VM (10.88.5.82)
Results: Ping and traceroute test from 10.26.8.230 to 10.88.5.82 works as expected (PASS)

Test 4: From Private Gateway VM (10.88.5.82) to L2 VM (10.26.8.230)

Results: Ping and traceroute test from 10.88.5.82 to 10.26.8.230 does not work (FAILED)

We've been trying to debug Tests 2 and 4 for a while now with no sucess. Anyone has any ideas?
Or is Cloudstack designed not to allow this to be possible?

##### STEPS TO REPRODUCE

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NA
~~~

##### EXPECTED RESULTS

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Tests 2 and 4 should be able to work
~~~

##### ACTUAL RESULTS

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Tests 2 and 4 does not work
~~~

从已记录的 Advanced Networking、VPC、L2 Network 和 VNF (PFsense) 配置开始，然后使用列出的 ping 和 traceroute 路径重现 Tests 2 和 4。完成意味着确定非对称可达性是 CloudStack 缺陷还是预期行为，并记录已确认的 fix 或配置要求；未指定源文件或测试。

由索引模型根据 Issue 内容生成。