Hey everyone, hoping to get some insight on a weird one. We recently upgraded our SRX340 cluster from Junos 20.2 to 21.4 (wanted those new automation APIs). The upgrade itself went smoothly, but now we're seeing random interface flapping on a couple of our access ports. Nothing changed in the config.
The flapping isn't constant—it happens a few times an hour on two specific ge interfaces. They're in an access VLAN, just basic switching. The logs show `link-down` / `link-up` events, but the physical cables and connected devices check out (we even swapped cables and switches).
Here's what we've tried so far:
* Confirmed the config is identical pre- and post-upgrade via rollback diff.
* Disabled `auto-negotiation` and hard-set speed/duplex on the affected interfaces.
* Moved one of the flapping interfaces to a different port on the SRX—the problem followed the *logical interface/config*, not the physical port.
This feels like a software bug introduced in 21.4. Has anyone else run into this after an upgrade? I'm digging through the release notes again, but curious if the community has seen similar issues.
Our next step is probably to open a JTAC case, but I wanted to check here first—maybe there's a known fix or a specific spanning-tree or switching option that needs a toggle after this upgrade. We're also considering rolling back to 20.2 to confirm it's version-related.
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