In my setup I have 2 different interfaces, one for WiFi and another for 4G/LTE. Both are USB dongles. I'm using Ubuntu 16.04 at the moment, but that can change. In my problem I need to mantain an IP session, meaning that when I go out of a WiFi hotspot coverage area I need to automatically change to LTE (and viceversa) in a transparent and lossless way. That is supposed to be acomplished having the same IP for both interfaces, since a change in the IP would bring packet loss.

Both interfaces have different subnets and gateways. WiFi is in while LTE is in This is a fixed setup, since WiFi addres depends on the WiFi network, and LTE addres depend on the cellular provider.

I have tried bonding, but I've read that it is necessary to have both interfaces in the same subnet, since it is not "IP level routing". I tried using aliases or configuring two different gateways, but nothing has worked so far. I also saw something about making a bridge, but I read it wouldn't work with WiFi.

So my question is: How could I make both WiFi and LTE interfaces on different subnets work as one unique interface, or at least make them work as a fault-tolerant system? Is it possible through bonding? If not, is there another way?

Thank you very much in advance.


There’s no chance it can work that way.

IP addresses in are not routable on the Internet. This means they are not “real” IP addresses, and get rewritten by some middlebox in you ISPs’ networks to “real” IP addresses, in a process that is called NAT44 (or, more accurately, NAPT44). Hence, even if both interfaces were using the same IP address in, a connection could not migrate flawlessly between networks.

What you’re willing to do is called multi-homing. It could be possible if the same ISP were managing the WiFi and LTE networks, although I doubt any mainstream ISP will do it.

With distinct ISPs, it should still be possible if you could obtain a PI (provider-independent) IP address from your RIR (regional internet registry) and then convince both ISPs to allow you to use your PI address and establish a BGP session with them.

I think the most realistic option is to use a VPN so the inner address can be stable when you change your outer connection.

  • I have acces to the core LTE network, like the ePDG or the PGW, so I may be able to see those "real" IP addresses you mention. Couldn't something similar to NAT work? Like making the NAT change the IP address when going in/out the inner network. – Iván G Apr 17 '17 at 12:09
  • I don’t know much about LTE networks and have no idea what you call ePDG and PGW. – user2233709 Apr 17 '17 at 12:14
  • Those elementes are Packet Gateways that give the LTE network internet connectivity. Anyway I think it is not that relevant. I will try to investigate about PMIP, that seems to be what I'm looking for. Thanks for your response, although not solving my problem I learnt from what you told me! – Iván G Apr 17 '17 at 12:44
  • I don’t know PMIP but at first sight, I agree that it looks relevant. Seems it looks somewhat like a (non-encrypting) VPN. Anyway, I’m glad if my answer could help you. – user2233709 Apr 17 '17 at 13:03

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