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I was recently thinking about how I would go about connecting two separate buildings using optical fiber cables. This is mostly for understanding how this would be done to further my mental horizon, not because I actually need to do this. I have never before worked with fiber or PPP, so my knowledge in this area is quite limited.

My first plan was to put a router in each building and connect them with a fiber cable. They would then exchange IP (and other) packets via ethernet. I guess this would work fine and I can find plenty of clues on how to do this on the internet. Specifically I can find offers to buy SFP fiber cables and matching ethernet cards and I guess if I would plug those cables in those cards they would be able to communicate pretty much like any other ethernet connection (right?).

But then I thought: Wait, I have only two routers communicating with each other over this connection, so isn't at least the addressing part of ethernet unnecessary for this? Maybe there's a layer2 protocol that is better suited for this! I searched the internet about this and found, that PPP apparently is such a protocol for communication between exactly two nodes.

However, when I tried to find out how exactly I could communicate via PPP via fiber (i.e. without ethernet), I found some mentions that PPP over fiber is possible and then lots of tutorials on how to use various tools to connect to my ISP via PPPoE and some other use cases that don't involve fiber at all. I found no information about what kind of hardware I would need to do this or if I would need any special software to set up the connection.

This scarcity of information about this lead me to question even more if this is actually a good idea. Is PPP actually something I should consider using for this use case or am I overthinking this and should just use ethernet or something else entirely?

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PPP is a protocol for transporting higher-layer protocols (like IP) over a simple serial interface. Since you'd already be running Ethernet, PPP doesn't work and is of no use anyway. You could use PPPoE but still without gain.

Simply run Ethernet and IP on top and you're fine. All you need are routers or switches with SFP interfaces, suitable SFP transceivers and the right cable. Of course, you need to use IP addresses on the link but private addresses are free to use. Config, stir, enjoy.

In case you're worried about the security of the fiber outside a building: PPP or PPPoE doesn't help with that at all. You'd need an encrypted tunnel link, usually called VPN.

Is PPP a useful choice for fiber connections?

Not really. PPP requires an underlying hardware interface that most likely is expensive and hard to acquire - also think of a spare or replacement in a few years.

Ethernet is available in an extremely wide variety of speeds and distances and it's very low priced. By performance and by budget there's no real alternative for lighting fiber.

  • I was actually trying to ask if it makes sense to run PPP instead of ethernet. – Kritzefitz Sep 13 at 20:52
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    Ethernet would be simpler to configure and maintain than ppp. – Ron Trunk Sep 13 at 21:58
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    @Kritzefitz Are you worried about performance or about efficiency? For the former, just take the next faster Ethernet PHY. – Zac67 Sep 14 at 7:51
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    @Kritzefitz, a router will not ARP with every packet sent. A Cisco router ARP cache timeout is four hours (14,400 seconds) by default. If you are worried about sending an ARP every four hours, then you are worried about nothing. You could set the ARP timeout as high as 4,294,967,295 seconds, which is over 8,000 years! – Ron Maupin Sep 14 at 14:25
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    @Kritzefitz, remember that the interface dictates what protocol can be used, and your SFPs plug into an ethernet interface, so they run ethernet. Some routers have other slots into which you can plug a variety of interfaces, many of which can be quite expensive. For fiber, there are expensive PoS cards on which you can run PPP, but it simply isn't worth it, and they are going to be hard to get, and they do not connect to an SFP slot. – Ron Maupin Sep 14 at 16:32

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