Introduction and Background
The local ISPs in my company's neighbourhood only offer 125Mbps maximum upload per WAN connection because fibre has not yet been implmented. We have more than 1TiB of essential data to push to an off site location- preferably within a one day period. Our off-site location has approximately 300Mbps download speed.

We have two WAN connections, one for WiFi, one for the server network, each at 125Mbps upload. My thought is, what if the traffic was split across two interfaces, both connected to a separate LAN, connected to a separate WAN.

How can I utilize the upload speeds of these two networks most effectively? My ideas so far:

  • Purchase a second static IP on each modem and assign each interface's MAC address a public IP, then setup some sort of round-robin or load distributed routing (suggestions welcome).
  • Follow a similar trend as above but utilize a VPN and a second piece of routing hardware on the other end.
  • Pay for an SD-WAN aggregator service: https://itel.com/sd-wan/
  • Find a way to make this happen with two network interfaces on the main backup server.
  • How are you connected to off-site? What application do you use to push data? Is it one large file, or multiple files?
    – Abu Zaid
    Sep 15, 2021 at 12:03
  • Hey Abu, my backup application is Proxmox Backup Server pushing to another remote instance via a single TCP port. So, lots of block data from a block storage (VM and LXC virtual disks).
    – Tmanok
    Sep 15, 2021 at 17:45

1 Answer 1


The biggest factor in your scenario is your backup application. If your application makes a single connection (i.e. a single TCP flow) to the destination, there's little you can do to speed things up. Any attempt to "load balance" across multiple connections is likely to cause out of order packets and slow things down.

The good news is (based on a quick calculation) that with one 150Mb stream, you can upload all your data (ideally) in about 15 hours.

If you application supports multiple connections, it may be possible to spread them out over multiple links, but it will require extra hardware/software on both sides. If you can live with 15 hours, that would seem to be the way to go.

One more thing: do not use WiFi for your backup: WiFi is half duplex, and you will struggle to get 150M throughput.

  • Hey Ron, thanks for your answer. 1. The backup is Proxmox Backup Server connecting via a single TCP port. 2. Certainly won't use WiFi, the secondary modem simply serves a bunch of access points in our head office so that the network is separate (a design choice before my time), I would certainly be connected via Cat6. 3. 125Mbps, makes that a little longer and I would also need to reserve some bandwidth for serving clients, I should have made that clear. Thanks Ron!
    – Tmanok
    Sep 15, 2021 at 17:43

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