networking question

[Martin Kletzander]

On Thu, Feb 24, 2022 at 07:07:18PM +0100, Natxo Asenjo wrote:
>hi,
>
>I have an issue with one host at a customer's site. I think this cannot
>work, but I would like to ask you just in case I am confused.
>
>host:
>eno1: 172.20.10.x/24 management interface gw 172.20.10.254
>bridge-service: 0.0.0.0/24
>tun0: openvpn tunnel to external data center
>internal-bridge: x.x.x.x/28 ; routed subnet that goes to openvpn tun0
>
>on vm:
>eth0: x.x.x.x/28 on internal-bridge (default gw)
>eth1: 172.20.10.x/24 bridge-service gw 172.20.10.254 (same as eno1)
>
>Connectivity to and from openvpn (from and to datacenter) is perfect. All
>vms are directly reachable from our management services, no natting.
>
>>From hypervisor I can ping the gw, from vm I cannot ping 172.20.10.254.
>
>My gut feeling is that this cannot work because traffic for the hypervisor
>for subnet 172.20.10.x/24 flows through eno1, but for vm through the
>bridge-loggin interface. So that cannot work.
>

I am not sure, but I would try to see where the packets are really going
through by using wireshark/tshark or tcpdump.

The only thing that I can come up on the spot is that it is trying to go
through different interface at some point due to reverse path filtering,
settings for that are in /proc/sys/net/ipv4/conf/*/rp_filter, it might
be routed elsewhere anywhere along the way.  But it is hard to say
without knowing how all the networks are connected.  Maybe I'm just bad
at understanding your situation, for me it is usually better to see this
stuff happen in wireshark.  But I figured I at least let know know one
idea which we had an issue before as well.

Hope that helps,
Martin

>Should we just ask the customer to give us different subnets for the host
>and the vm?
>
>TIA.
>--
>regards,
>Natxo
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