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Comment by franga2000 | Hacker News Reader

franga2000

Not my field, so I might be making an obvious error here, but:

If there are efficiency gains to be had from using jumbo frames, wouldn't setting my MTU to a multiple a 1500 still be of some benefit? If my PC, my switch and my router all support it, that would still be a tiiiny improvement. If the server's network does as well and let's say both of our direct providers, even if none of the exchanges or backbones in between do, that would still be an efficiency gain for ~10% of the link, right?

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Locally you can set your MTU to larger than 1500, but if you (generally) try and send a packet towards the internet larger than 1500 it will be dropped without a trace, or it will be dropped and an ICMP message will be generated to tell your system to lower the MTU. Assuming you have not firewalled off ICMP ;)

As a handy feature on Linux at least, you can set your MTU to 9000 locally, and then set the default (internet generally) route to have a MTU of 1500 to prevent issues:

ip route add 0.0.0.0/0 via 10.11.11.1 mtu 1500

Over-sized packets can (and generally will) be fragmented by your router. It shouldn't be dropped unless you've intentionally set DNF.

Fragments are very hit or miss on the internet, https://blog.cloudflare.com/ip-fragmentation-is-broken/

They will fragment them but many times you will see performance or other misc issues ... eventually.

AFAIK, most OSes today set DNF by default.

Oh I never knew this. I wonder if I could enable Jumbo Frames to stream 4k content more efficiently on my local LAN.

You could...if the software on both your server and your media pc support large frames. And you're willing to deal with every once in a while some piece of software doing the wrong thing and sending out every packet with large MTU without doing detection on max packet size.

Huh, I wasn't aware that dropping large frames was so commonplace. I guess they don't want to use the CPU cycles to fragment them?

Potentially but troubleshooting performance issues from mismatched MTU can be brutal so most providers drop anything over 1500.

Many devices can do over 1500 but anyone who has done so without careful consideration knows the outcome isn't predictable unless everyone on the network is prepared to do so.

A dedicated / controlled SAN type environment can do it just fine, beyond that it can be difficult.

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