configuration with multiple iface's in Linux

Question asked by William Allen - 9/11/2026 at 9:23 AM

Unanswered

I have my smartermail server on a Almalinux9 system and have two iface's setup on the server. A Public network and a Private network. The Public network is for users to use Smartermail, the internal network is for file storage.

The issue is when I turn on the internal iface, Smartermail stops responding to web requests, ie site cannot be found. When I turn the internal iface off web traffic routes properly again.

I have setup route statements for each iface but again Smartermail, even though all services are bound to the external ip address won't route properly when the internal iface is turned on.

I am sure it is a simple fix but my brain is broken because I can't get it to work. Anyone have an Idea of what I need to do to get it to work?

3 Replies

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Nathan Replied

9/11/2026 at 2:35 PM

First thought would be, do you have a default gateway specified on the internal interface? If so, remove it.

William Allen Replied

9/11/2026 at 5:14 PM

I did, I removed the default gateway but left the route statement with one. It seems to be working now. Thanks for the thought.

John Quest Replied

9/12/2026 at 10:49 AM

I did, I removed the default gateway but left the route statement with one. It seems to be working now. Thanks for the thought.

Any time you have a computer that is multi-homed, you are opening the door for problems. You have to take extra steps to thoroughly map out and check everything to mitigate and prevent those problems.

For example, I have 2 HYPER-V hosts that have 11 NICs.

2 for ISCSI storage with 2 reserved for future expansion
3 for HYP-V DMZ setup as a TEAM for VMs for the DMZ with 1 reserved
2 for DMZ-INFR for intra-HYP-V communications on the segregated DMZ-INFR zone
1 for iDRAC

I have and maintain a detailed document for EACH server listing all installed NICs, their groupings, configuration, purposes and so forth.

ANY configuration change requires the proposed change to be "penciled in" on the document and then carefully reviewed for any potential issues.

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