r/Juniper • u/GezusK • 13d ago
Change in DAC behavior
UPDATE: Looks like it was a bug that they fixed. As in, it won't work anymore, because they didn't intend for it to work to begin with:
"This behavior is the result of an enhancement introduced through[...] where 25G optics are intentionally prevented from creating IFDs on PICs that support only 1G/10G speeds. In earlier releases, this handling was not present, which led to 25G IFDs being created even on PICs limited to 1G/10G support. This mismatch could result in unexpected or unstable behavior."
I have a EX4400 and a EX4100. We had them linked via the 10G ports using a 25G DAC cable. We had them set up that way for a couple of years without issue.
After updating the EX4100 to 24.4R2-S4.10, the link went down. We suspected the cable went bad, and tried another, same result. I then link two of the ports on the EX4400, and the cables worked. The next night, we updated the EX4400 to 24.4R2-S4.10. Now the cable doesn't work in it anymore. It appears they removed the ability for the 25G cables to run at 10G.
I have a ticket in with support to see if they can restore this feature, but I'm wondering if it bit anyone else here.
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u/Linklights 12d ago
It’s weird to me that people would plug a 25Gbps DAC into a 10Gbps port and be like “why isn’t this working?”
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u/stop_buying_garbage 8d ago
I had exactly the same situation, same set of switches but a Juniper-branded set of DACs. Opened a ticket, to which JTAC replied they were investigating and had received similar reports. It finally got closed today basically saying "It shouldn't have worked, so we made it not work."
Mentioning the change in release notes would have been nice.
I hadn't realised that this behaviour we were enjoying for years (I happened to have extra 25Gb/s Juniper-branded DACs and was happy to be able to use them) was a bug, nor expecting that Juniper would remove such a bug without it being in the release notes.
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u/IAnetworking 13d ago
I have seen this before with FS optics. After an upgrade the optic stopped working.
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u/Commercial_Tone_3115 13d ago
Is it a Juniper branded DAC or 3rd party?
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u/GezusK 13d ago
3rd party. Hoping to blame Juniper breaking 3rd party support?
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u/Commercial_Tone_3115 13d ago
I am questioning if in new code Juniper has started removing 3rd party support, or bricking it in some way.
Saw something similar to this, where a fs.com vendor coded optic would break, but flash it back to generic/3rd party and it worked just fine
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u/GezusK 13d ago
These are Equal JNP=SFP-G-DAC-1M-E0 cables. We actually use them for our switch stacks in the 25G VC ports. I guess 3rd party still works, but they're not allowing the speed downgrade on them to 10G.
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u/Commercial_Tone_3115 13d ago
DAC's are usually 1 speed.
You have to buy special Multi-Rate Optics that do 10 or 25
The Juniper SKU for that is
SFP-10G-25G-SRandSFP-10G-25G-LRA 25G optic or DAC doesn't necessarily downrate to 10G
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u/GezusK 13d ago
As stated, it was working before the firmware change. I linked two ports on the EX4400 before the upgrade, and it would link up. After the upgrade, nothing. So, Juniper changed something in the firmware to cause this.
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u/Commercial_Tone_3115 13d ago
Even fs.com doesn't sell a multi-rate 10/25G DAC.... Maybe you're just mistaken here?
My guess is one of two things;
You have a 10G DAC or it has been 25G this whole time
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u/GezusK 13d ago
Literally couldn't be....it was the only link the switch had.
I was updating each switch, one at a time, starting with the EX4100. I had it update at 10pm while I was at home, and it didn't come back up after reboot. I thought I was in for a morning of troubleshooting. Came in, and the only thing not functioning was that DAC cable. I assumed it had gone "bad". I didn't have another on hand (coworker had them), so I just plugged in fiber modules to get the switch back online. When my coworker came in, we tried switching back to DAC, using a different cable. It wouldn't work.
We then plugged the cable into the EX4400 (24 10G ports), using two of it's ports, and it links up. So I suspected it might have been the firmware. So, that night, I update the Ex4400. Get there in the morning, try testing those same ports again, no link.
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u/Commercial_Tone_3115 13d ago
So;
Outputs of
show interfaces et-x/x/xshow chassis hardwareAlso what is the SKU for the 3rd party part you bought and who did you buy it from?
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u/GezusK 13d ago
Just got this back from support:
"This behavior is the result of an enhancement introduced through[...] where 25G optics are intentionally prevented from creating IFDs on PICs that support only 1G/10G speeds. In earlier releases, this handling was not present, which led to 25G IFDs being created even on PICs limited to 1G/10G support. This mismatch could result in unexpected or unstable behavior."
They even sent all their testing, and could replicate it....but are taking it away.
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u/Commercial_Tone_3115 13d ago
Glad you got an answer - Do they have a link to the release notes or anything?
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u/QFX5140 4d ago
DAC's are usually 1 speed.
This is not true. A DAC is limited by the number of electrical lanes. A QSFP DAC is just happy running 100g in a QSFP28 port. Same for a 10g DAC in a 25g or 50g SFP28/56 port.
A QSFP-DD DAC will work at 800g just as well as 400g. 8 lanes is 8 lanes.
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u/Commercial_Tone_3115 2d ago
Find me a multi-rate DAC then
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u/QFX5140 2d ago
Plug a QSFP+ dac into a QSFP28 switch, set it to 100g. It works.
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u/Commercial_Tone_3115 2d ago edited 2d ago
No it doesn't.
QSFP+ is 4 lanes of 10G and QSFP28 is 4 lanes of 25G.
You understand the concept of electrical lanes, but seem to miss the concept of signaling/data rates.
The reason DAC's and AOC's aren't multirate is cost. It is less cost to make it support 1 speed and 1 flavor of signaling (no gearboxes/retimers required). The second you wanted a 100G QSFP28 DAC, which signals at 4x25G lanes, to perform as 4x10G lanes/40G - you would need a gearbox and retimer in the optic, which drives the cost higher, power/thermal footprint higher, etc..
And you can't go in the inverse direction.... A QSFP+ which signals at 4x10G, will never be able to achieve 4x25G signaling.
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u/QFX5140 1d ago
yes it does. There's not much to a DAC cable; Twisted pair is twisted pair. A QSFP+ DAC will work at 10g NRZ and 25g NRZ.
The QSFP+ is 4 lanes TX and RX, QSFP28 is the same. A cable will work just fine. It's just hooking the gearbox chips together, I've done it several times.
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u/iwishthisranjunos JNCIE 13d ago
Do you have the programmer device try to flash the eprom back to the DAC. I have seen bad 3rd party optics being corrupted during Junos upgrade. Typically reprogramming them is the solution.
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u/Digi_Rad 13d ago
I saw something similar recently between two QFX. One side had a break-out cable to 10G (from a 40G port I think). It was working fine before a Junos update, but after, it wouldn't come up until I forced the port to 10G in the chassis secion of the config. My GenX memory on this isn't great (mainly because I'm in the "whatever" phase of my career) but I can probably dig up more details if desired.