On Mon, 9 Mar 2026, Carl Fredrik Lagerfeldt via NANOG wrote:
Is 9530 a good value? What would you configure? (Am I simply overthinking this?)
I did a very brief overview of this a few months back, and found several references to 9600. https://business.comcast.com/support/article/ethernet/wavelength-service being one of them. "Transport interfaces can support frame sizes of up to 9600 MTU. " Not sure what "frame size" is in this context exactly, if's calculated with 14 bytes of ethernet header or something else. https://www2.arelion.com/ethernet-vs-waves-flyer , 1299 also say 9600 on DWDM (but it seems you're now saying you could support more?) I don't think we generally can agree on a frame size in this industry, 4470 and 9180 were the IP MTUs of classical old transport, but nothing say we should stay there. So 9530 sounds as good as any. Just define it well so everybody knows what's up. I've tried asking several providers what their number means, if it's L2 or L3 MTU they're mentioning, and generally the provisioning/installation people don't know the difference so I've had to empirically test what it was between those two variants. -- Mikael Abrahamsson email: swmike@swm.pp.se