10Gigabit Total bandwidth

This might be a noob question. Wanted a clarification on 10Gigabit links. Is a 10G link, 10G up and down or 5G up and 5down or just the sum of up and down should total to 10G? Reason I’m asking this is i’m noting increase in latencies whenever total traffic on one of my links is at 4G up and 5G down. I’ve noted this on different switches different 10G links as well.

I think it is 10 down and 10 up. Because its either in duplex mode (10gb down and up) or single mode (10 gb down or up)

10gb Ethernet supports only full duplex. This means bidirectional communication at 10gb both download and upload.

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Yeah generally everything these days is full duplex (i.e…, rated speed in both directions at same time).

A notable exception being some fibre broadband services which are run using only a single fibre (not a pair) - they’re half-duplex.

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Ugh, I think the term for network bandwidth is symmetric vs asymmetric (or at least used to be).

Home fiber uses a single fiber, true. But different wavelengths for upload+download. It’s full duplex in a radio-ish sense in that you could simultaneously be transmitted and receiving data, but it’s a shared medium.

There are a gazillion varieties, it’s not even funny, GPON, XGPON (aka 10G-PON), XGS-PON (10G symmetrical), and 50G-PON.

XGS-PON seems to be the most common one these days, where everyone on the fiber shares 10G down and 10G up.


Anyway, back on topic, on these full duplex systems, how much “upload speed” you get is purely a function of payment plan/package you’re on. … and sometimes your neighbors (due to oversubscription).


One reason your download speeds might be suffering is that perhaps your PC or firewall isn’t powerful enough to deal with it.

@dngumo if you suspect issues, can you try testing with iperf3 ... --bidir?

As a quick reminder:
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@risk it’s not an ISP link. It’s fiber from a locally hosted Nexus switch to another. Transceiver is 10G SFP+ LR . Using for storage and vm network, and the servers themselves have 10GSFP+ DAC cables to the switches. Whenever total up and down is 10G (e.g 4G up 6G down) that’s when I see latencies which I thought was odd. I will take up your suggestion of testing using iperf

If you are experiencing latency, it may be your machines if the CPU is doing the heavy lifting.