Hit 500 VLANs on a single switch stack, never thought I'd see that day

I was doing a cleanup on a client's network last week, a big manufacturing plant out in the industrial park near me. They've been adding little subnet after subnet for new machines and security cameras, all on the same switch stack. I ran a command to list the VLANs just out of curiosity and bam, 500 exactly. That surprised me because the switch documentation says the max is 1000, but I always figured you'd hit some weird bug or performance wall way before that. The reason it mattered is that I had to completely rethink how they do their voice VLAN and DHCP relay setup, because some of those older switches in the stack were getting confused. Has anyone else pushed the VLAN limit on big stacking setups like a Cisco 3850 or similar? I want to know if I should start planning a hardware upgrade now or if this is normal.

3 comments

3 Comments

cole_bailey851d ago

500 VLANs exactly" that's a wild coincidence. Were those older switches in the stack actually running out of memory or just acting flaky with the config?

tessa_roberts123h ago

Dig into the syslogs on those older switches to see if they were throwing memory allocation failures or just hitting max MAC address table capacity. I've seen stacks start dropping frames when the CAM table gets too full, but that usually shows up as intermittent connectivity way before 500 VLANs. Was there a specific pattern to the flakiness, like certain VLANs getting weird during ARP floods or spanning tree reconverging for no reason?

webb.val23h ago

Falls right in line with that universal rule where things always break at the worst possible time, lol. It's like how my washing machine only dies right when I have a full basket of work clothes, never when I'm doing a single load of towels. Those switches probably held on just long enough to make you think everything was fine, then hit their limit at exactly the wrong moment.

-1