25 Gigabit Linux internet router PC build

Re:25 Gigabit Linux internet router PC build by bcrl on Saturday July 10, 2021 @12:08PM (#27794346)

That's not entirely true. SFP power consumption depends on the type of SFP. A 10Gbps DWDM SFP+ might draw 1.8W of power. The why for this is actually quite interesting: the lasers used in DWDM SFPs have much more stringent requirements for temperature stability to ensure the light emitted doesn't drift out of spec. In order to achieve that temperature stability, they use a built in peltier to pump heat away from the laser and control the temperature. They're quite the marvel of modern engineering!

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Re:25 Gigabit Linux internet router PC build by oasisbob on Saturday July 10, 2021 @12:29PM (#27794521)

It would have been fun to be a fly on the wall at Cisco when they first realized people were jamming devices with heaters in SPF sockets.

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Re:25 Gigabit Linux internet router PC build by eqvinox on Saturday July 10, 2021 @04:54PM (#27796393)

Cisco didn't "realize" this was happening, they specified, had manufactured, and sold the very SFPs the GP post is describing. SFP slots in routers are designed with this thermal load in mind.

Which is also why plugging a large amount of DWDM optics into a datacenter switch is a bad idea. Datacenter switches are _not_ designed with this in mind. You run into risks of both overheating the switch as well as overloading the PSUs. A small number of high-power optics ain't gonna break the switch though.

And: 10Gbase-T SFPs have horrendous power consumption, even worse than DWDM SFPs. At these speeds, the signal over copper is mostly mush, and the PHY contains a none-too-trivial analog & digital signal processor. Which, again, is where limitations for 10Gbase-T SFP usage come from. If at all possible, avoid this shit — there's absolutely no reason to have 10Gbase-T inside a rack, for example. Just use DAC cables or SR optics.

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Re:25 Gigabit Linux internet router PC build by oasisbob on Sunday July 11, 2021 @12:43PM (#27802376)

I'm being a bit glib, but from the point of view of someone who used SFP optics once in a while, it seemed like the whole "standard" was a bit of a mess.

If it was known that vendors would try to push their thermals past what the device cage would support, why not address that better?

The general impression I was given is that thermal loads were one of the primary reasons given for vendor-locking pluggable optics, and that the original SFP spec didn't even address it.

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Re:25 Gigabit Linux internet router PC build by tomnipotent on Saturday July 10, 2021 @12:43PM (#27794651)

Except no one is using DWDM for homelabs, as it's usually used for longer distances. The peltier cooler is definitely cool, though.

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Re:25 Gigabit Linux internet router PC build by bcrl on Saturday July 10, 2021 @01:12PM (#27794886)

True. On general principle I would recommend folks invest in single mode rather than multimode fiber for permanent installs, as the price delta on SFPs is low enough these days. Multimode is a complete pain as it needs to be upgraded for higher speeds every decade. If it's just a couple of patch cables in a home lab, it doesn't matter, but if it's run through a wall...

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Re:25 Gigabit Linux internet router PC build by gonesilent on Saturday July 10, 2021 @08:38PM (#27797547)

It's also a real laser versus a many sfp+ gbics being LED light source now

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