Overheard a network engineer say 'MTU is always the problem' and it clicked for me

He was talking about a random site outage at a warehouse in Denver, and after chasing it for hours he found the firewall was fragmenting packets wrong. Has anyone else had a stupid MTU issue that took way too long to diagnose?

2 comments

2 Comments

parker_campbell21d ago

Oh man, YES. I had a situation with a client's VPN that would randomly drop connections for like 3 minutes then come back. We spent weeks blaming the router, the ISP, even the weather. Turned out some moron had set the MTU on their end to 1400 instead of 1500. Every time a file transfer hit that sweet spot the packets would get shredded. That was a full Saturday I'll never get back.

lisa_murray21d ago

Man, that MTU thing. I gotta be honest, I used to roll my eyes when people blamed network settings like that. Thought it was just geeks making stuff up to sound smart. "Your MTU is wrong" sounded like some made-up excuse to me. But then I had a customer with this weird voip issue where calls would drop after exactly 47 seconds. Nobody could figure it out for months. Turns out some manager had changed the MTU to 1450 "to make things faster" and it worked fine for everything except calls. Completely changed how I look at those little number settings now. You just never know what dumb human decision is hiding in there.