SSH connection between VM's accross different VLAN's while using Firewall

HellrazorX

Member
Oct 14, 2021
24
4
8
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Hi,
I read over some other threads that this issue is known but the solution does not seem to be official. That's why I'm posting this one.

Example: VM1 on vlan30 and VM2 on vlan60

- VM1 can ping VM2 (and vice versa)
- VM2 cannot ssh VM1... But VM1 can ssh to VM2
- PVE firewall is activated

When PVE Firewall is disabled, everything works.
---

I think this problem arises only when trying to communicate across different VMS using different Vlans on the same node.

If I migrate the vm to another node, SSH starts working again.
---

So far, I found out the problem is known and the suggested fix could be:

in host.fw:

[OPTIONS]
nf_conntrack_allow_invalid: 1enable: 1

I didn't test it yet but I really don't understand this parameter and what it can possibly compromise from a security stand point.


Anyone?
 
Hi,
I read over some other threads that this issue is known but the solution does not seem to be official. That's why I'm posting this one.

Example: VM1 on vlan30 and VM2 on vlan60

- VM1 can ping VM2 (and vice versa)
- VM2 cannot ssh VM1... But VM1 can ssh to VM2
- PVE firewall is activated

When PVE Firewall is disabled, everything works.
---

I think this problem arises only when trying to communicate across different VMS using different Vlans on the same node.

If I migrate the vm to another node, SSH starts working again.
---

So far, I found out the problem is known and the suggested fix could be:

in host.fw:

[OPTIONS]
nf_conntrack_allow_invalid: 1enable: 1

I didn't test it yet but I really don't understand this parameter and what it can possibly compromise from a security stand point.


Anyone?
anyone?
 

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