Dual Nic Server LibreNMS listen on ip

My server has dual nics, different subsets.
But seems that librenms website only listens on nic 5.x when my computer is sitting on the 5.x vlan. Anyway to make librenms listen only .1.x from a device on the .5.x vlan?

Hi @07stuntar1

This is not specifically a Librenms issue, it’s a networking one.

If you think about it, what is happening is correct.

I’m going to assume that the server’s default gateway is on the .1 subnet?

If so, when the server receives a packet from any subnet other than .1 or .5 what does it do? It sends the reply to the default gateway to be routed to the correct destination.

If it receives a packet on its .1 address from a host on the .1 subnet, what does it do? It sends the reply directly to that host.

Now, when you send a packet from a host on the .5 subnet to the server on it’s .1 address, you are expecting it to reply via it’s gateway, like this:

client > client router > server router > server .1 address > server router > client router > client

However, the server sees a packet from a .5 IP address, well it is directly connected to that subnet, so it will reply to the host via it’s .5 address. The client gets a reply from the .5 address that it is not expecting an drops it.

The upshot is this, if your client is on the .5 subnet then it can only talk to the .5 address of the server. (technically there are a few ways around this, but I’m not going to get into that)

Hope that all makes sense.