Haven't tried it (yet) myself but sounds interesting.
I wonder how many routers are filtering IPv4 packets with fragment offsets of 8190 and 8191?
I think it was done just for fun. It is slightly concerning that a live equipment has such a joke enabled, but I'd say its fun-to-price ratio is relatively high.
Also: IIRC IP packets contain CRC's/checksums of some sort. I'm not sure if the poster corrected for that or maybe the other side does(n't) and somewhere the CRC doesn't check out and thus the packet is dropped/invalid (or maybe even somewhere along the way by at a hop that chokes on such bit)?
True story, some years ago I had to design a protocol for remote configuration using text messages. We used a char to send the status in a compact format but in the first version we used only the first 3 bit and we specified that all the other bit should be zero (we have done so in order to have a predictable default in the future and also to increase the readability of the logs). After few months in the field we noticed that using an additional bit would be useful. Don't want to go into many details, not a problem if the bit is ignored but nice to have to simplify the operations. We updated the protocol, issued the new specs, the vendors develop the new version, we test the new version and surprise: the IOT between the new server and the old client was broken. Why? Because the designer the implementer of the client was to strict on the must be zero clause and decided that a packet with a one was a corrupt packet and should be dropped.
The result was a slow campaign of firmware upgrade and a 1 year delay of introduction of the new protocol. And it was a closed system where we had full control of clients and servers. Imagine what happens with open systems.
By the way, it is an application of this principle: https://en.wikipedia.org/wiki/Robustness_principle
Also, as barosl observes (https://news.ycombinator.com/item?id=10633361): "but I guess if one is following the RFC rigorously, dropping packets with the reserved bit enabled is the correct"
I love that anyone's implemented it at all though, and I really hope it's deliberate on the part of the people who drop the packet.
Similarly I have had a page online for years (may still be, can't remember the exact url... so I'd have to dig a little) that was served with HTTP status
418 I'm a teapot
This made it easier for manufacturers of IDS/IPS/UTM/NGFW equipment to quickly isolate false negatives during fully loaded tests.