Ethernet Frames Feelings

The Day I Learned Ethernet Frames Don’t Care About Your Feelings

Working at Florida Blue, I had to debug why medical images were getting corrupted during transfer. After three days of blaming the application layer, I finally broke out Wireshark and discovered that Ethernet was silently truncating our jumbo frames because someone forgot that not all switches in the path supported 9000-byte MTUs. The frames were being chopped like a bad haircut, and TCP was just reassembling the carnage and hoping for the best.

Ethernet is brutal in its simplicity - it’s basically just shouting bytes into the void and hoping someone’s listening. There’s no guarantee your frame will arrive, no guarantee it won’t be duplicated, and definitely no guarantee it’ll arrive in order. It’s like a postal service run by nihilists who’ve given up on the concept of reliability. The fact that we’ve built modern civilization on top of this chaos is either inspiring or terrifying.

The kicker was that the corruption only happened for files exactly 8192 bytes plus a few extra, because that’s when we’d hit the jumbo frame boundary and the last fragment would get lost. It was like a digital Bermuda Triangle for one very specific file size. The fix was setting the MTU to 1500 everywhere like it’s still 1985, because apparently, that’s the only size everyone can agree on. Sometimes the old ways are the old ways for a reason.