3 ms·
Why not use optical ethernet as ‘real’ cross domain solutions do? Probably cheaper if you don’t mind eBay, and gives you an easy upgrade path to 10Gbps or more
by bigfatkitten 10mo ago
Why not use optical ethernet as ‘real’ cross domain solutions do? Probably cheaper if you don’t mind eBay, and gives you an easy upgrade path to 10Gbps or more in future.
Two port NIC on the low side. Port 2 has its TX side connected to Port 1’s RX, just so the port will see a carrier and show link up. Port 1 TX goes to the high side machine’s RX, with TX left open.
From here, you have a whole ton of protocol options.
For things like syslog, you can just use a static ARP entry on the low side to forward events to the high side’s IP address via UDP.
For reliable transport, there are lots of options for reliable multicast now using erasure coding etc that don’t require a reverse channel.
- pragma_x 10mo agoThat's kind of brilliant. I had no idea that kind of thing would actually work. I always assumed that bidirectional connections were needed to allow ETH frames to function, electrically. I further assumed this applied to optical networking too.
- bigfatkitten 10mo agoFor 100BaseFX and 1000BaseSX at least, there’s no auto negotiation for link speed etc. As long as it sees a carrier from what it thinks is the other end of the link, it’s happy.
- mikewarot 10mo agoMy understanding is that there has to be a heartbeat sent in both directions for fiber Ethernet to work. There are work arounds, but then you're back up into the commercial product price range.
- bigfatkitten 10mo agoUsing a two port NIC on the transmit side as I described addresses this. This is exactly how commercial CDS vendors like BAE Systems do it.
- PaulCarrack 10mo agoIt's easier than that. You don't need two NICs to get a carrier, just use a fiber coupler. They are super cheap (< $30)
- bigfatkitten 10mo agoYou can, but a 1x2 multimode splitter is not something people generally have on hand, whereas 1000BaseSX cards (or media converters) and ordinary patch cables are easy to find.
- pseudohadamard 10mo agoOr you could get 10Mbps Ethernet hardware and cut the receive line. I don't know the specifics, including what particular Ethernet tech it was that allowed it to work, just heard someone talking about it some decades ago.