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Is it possible to use PPP (pppd) to create a network bridge between two subnets? That is, connect two segments of the same network, tunneling Ethernet frames, rather than IP packets?

As I understand, PPP is basically a fancy mechanism for sending data packets/frames over a serial line, so it seems it should be possible to use it for any kind of packets/frames.

To expand my question: I have a standard, home, local network which has a subnet like 192.168.1.0/24 with a router that runs a DHCP server. I'd like to connect another machine via PPP to this network so that it becomes a part of the subnet, for example:

  • It can request and get a DHCP address from the server.
  • It can access .local addresses in the network.

For this I'd like to create a network bridge using PPP over a serial line between this machine and another machine that is already in the network. I know how to create a bridge between interfaces in these machines, but not how to set up PPP to transfer Ethernet frames between them, if that's possible.

Petr
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  • Any reason why PPP? You can definitely do this with a VPN and L2TP. Are you using something other than IP? – Appleoddity Oct 16 '17 at 02:06
  • @Appleoddity It doesn't have to be PPP, and I'm using IP. But I'd like to understand various options, both theoretical and practical, to get better comprehension of how networking works in detail. VPN seems to be too high level. I'll look into L2TP, thanks for the pointer. – Petr Oct 16 '17 at 06:54
  • Understandably then, your request isn't super clear on what your end goal is. It's hard to give you precise answers when you don't have a specific topology and end goal in mind. This type of question isn't well suited to the question/answer format here. L2TP is VPN technology. – Appleoddity Oct 16 '17 at 14:48
  • @Appleoddity I understand, and I extended my question with more precise description of my goal. I hope it's better now, if not, I'll appreciate any further pointers how to improve it. – Petr Oct 16 '17 at 19:21
  • It is much better. But, just because I don't like to assume things - where is the computer you want to connect to your network located? Is it out on the internet somewhere? It does sound like you are describing a VPN scenario. One technology of which is PPTP, which might be what you are asking about? The last time I used PPP to connect a computer to another network like you describe I was using a 56k baud modem on Win 3.1. – Appleoddity Oct 16 '17 at 19:27
  • @Appleoddity No, it's not on the Internet (then I'd use OpenVPN or something like that). I want to connect it using a serial line - RS-232 or RS-485. – Petr Oct 16 '17 at 20:43
  • You are looking for something like a translating bridge. An example of which is a WAP that translates between ethernet and Wi-Fi, but you want it to translate between ethernet and serial protocols. Also, understand the you can have a DHCP server on a different network; there are DHCP relays to facilitate that. Extending layer-2 is rarely a good idea anymore. We now live in a layer-3 world. Where it used to be, "Switch where you can, route where you must," it is now the opposite. Layer-3 give you more control and security. – Ron Maupin Oct 16 '17 at 21:01

1 Answers1

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connect two segments of the same network, tunneling Ethernet frames, rather than IP packets?

I do not believe so, at least not directly(without a VPN or other additional encapsulation).

As I understand, PPP is basically a fancy mechanism for sending data packets/frames over a serial line.

Yes, but largely OSI layer 3 packet types that would normally go a layer above OSI layer 2(like Ethernet) frames, not raw Ethernet frames directly. There are corresponding PPP protocol numbers IP/IPX/IPv6/..., but not Ethernet.

rsaxvc
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