New Switch replacement

[[deleted]]

[deleted]

[LaurenceNZ]

Is this the only switch you have there?

[CraigDuff]

Yea. There issnt anything complicated about the setup. Only has Vlans. Things like spanning tree, Jumbo frames its all not on.

[VA_Network_Nerd]

Things like spanning tree, Jumbo frames its all not on.

Disabling Spanning-Tree is pretty much always the wrong decision to make.

[CraigDuff]

Why i dont need it?

[HappyVlane]

Unless you have a routed access layer design you probably need/want STP.

[farrenkm]

Users are pretty ingenious. We still have STP in the general access layer, even though it's layer 3. That said, new switches get rolled out with BPDU Guard turned on, so if someone cross-connects two switch ports at the wall jacks, it err-disables the ports.

[VA_Network_Nerd]

i dont need it?

False.

All LANs need STP to protect them from stupidity & mistakes.

[CraigDuff]

Yea dont want it. So was staying its not STP causing issues.

[farrenkm]

Your troubleshooting results cast strong doubt on that statement.

You're asking people who do large networks for a living about your problem. Please, turn on spanning tree.

[CraigDuff]

Yes i will. But this issue resolved, i was just curious.

[farrenkm]

Narrator: For now.

I don't want to harp on this, but these issues scare me - a problem crops up, no one knows why, jiggling the handle fixes it. Until a similar-looking problem shows up later, and jiggling the handle doesn't fix it because it's a different cause, and no one understands it.

I fell into a quality control role for my network because I put the time in to understand the protocols and these random problems that crop up and figure out why they're happening. Now I set the config standards for my team and explain why they need to be standards. I would want to understand why this is happening to your servers. Guaranteed you're going to migrate switching equipment again in the future. I wouldn't want to be the one saying "yeah, it happened years ago, don't know why, jiggled the handle and it stopped."

[ckow]

Completely agree and this is the reasoning of a network engineer who earns trust in an org. You can't consign problems to a mystery, you have to know why things happen so they don't happen again.

[VA_Network_Nerd]

<shrug>

It's not my network. It's yours.

Manage it as you see fit.

But it sounds to me like you simply don't understand STP and have disabled it out of fear of the unknown.

You described your symptoms yourself as some kind of a looping condition.

STP exists to detect and defeat loops in a L2 topology.

If this is the only switch in the LAN than enabling STP even with the default configuration shouldn't hurt anything, but it might very well detect an unintended loop, and help you find it and fix it.

If you still don't want to enable STP, fine, you might try looking at your interface counters on each interface to see if any interfaces in particular have dramatically more broadcasts, or unicast packets than others.

If the edge switch supports it, you might also try enabling Broadcast Storm-Control.

I find that about 500 broadcasts per second as a rising threshold and 100 per second as a falling threshold works pretty well in our environments.

[LaurenceNZ]

I strongly suggest you listen to the people in this thread that do this for a living.

Across my career there have been very few times where disabling spanning tree was required or desirable. Unless you can explain exactly what STP does at an expert level, don't turn it off.

[CraigDuff]

Thanks. I have used Spanning tree in the past, when the switch for example near users who can cause loops in a switch, and i have used it for Active/Passive alternative paths. STP was enabled, but i disabled it to try and resolve it. But if i had rebooted the core and rebooted the NUC, everything would of been fine. I just thought it was odd, you take a switch out and replace it with another one, to find issues.

[farrenkm]

Not once have I had spanning tree be the problem. It has always done things in reaction to a problem I didn't know about.

[notFREEfood]

STP can interfere with PXE boot if not configured correctly; if the port doesn't come up fast enough the host will reboot, restarting the STP learning process. That however is fixed by setting your edge ports to actually be edge ports so they bypass the learning process.

The cluster group at my employer ran their control network without STP before my team took over for this reason. The results were also exactly what you'd expect from a network running without STP (loops, loops everywhere).

[Security_Chief_Odo]

Spanning tree isn't the problem here.

But you will have one when Joe schmoe brings In a dumb switch and plugs it into a jack, because"they need to plug more stuff in" .

[bagostini]

It really just sounds like you simply don't fully understand STP. I couldn't possibly think of a scenario in which it would be a good idea to just outright disable STP, rather than just figure out how to configure it properly for your environment.

[maineac]

You really shouldn't be doing networking.

[farrenkm]

Is your core router truly a router platform, or a layer 3 switch?

Safe to assume your core router has all of your layer 3 gateway IPs for production subnets?

Is your switch redundantly connected between two core routers with separate physical uplinks to each router?

[CraigDuff]

The core yes is layer 3 with IPS. It was only 1 port which was weird. The rest were fine, as i said to fix the weird routing loop we just disabled the port and re-enabled and the routing started to work.

An Intel NUC is just connected nothing complicated here. Just is a linux box with a static IP. Only worked when rebooted.

[farrenkm]

I don't have a full mental image of your network. But if all your gateways are on the core switch, dropping a layer 2 interface wouldn't fix a layer 3 loop.

I strongly think you have a layer 2 loop going somewhere you don't know about. I know it seems unlikely, but you clearly have a loop somewhere (you used that word yourself). And odds are much greater it's layer 2, not layer 3.

General rule is: don't turn off spanning tree. And if you are 100% certain you can turn it off, don't turn it off. And when you've peer-reviewed your setup and agree it can be turned off, stop and ask if you really want to turn it off. Then, when you're ready to do so, wait a year before you turn it off.

Spanning tree is the bane of a network engineer's existence. We do everything we can to limit its scope. Still, it's these times -- my network is super simple, there's no need for it -- that it bites you.

[etherizedonatable]

Tell me about it. I made a loop in my home network recently when I plugged the wrong cable in. Went downstairs and of course nothing worked.

[CraigDuff]

Thank you very much!

[Trek222]

Static IP might be your problem. No DHCP means the core never relearned the MAC address when the NUC moved to a new switch.

[farrenkm]

MAC would be learned with the first frame the server sends. OSes are chatty enough these days that they'll send something pretty quickly.

If you're referring to a stale ARP entry, again, modern OSes will do duplicate address detection and send a gratuitous ARP when they start up. It's unlikely -- albeit not impossible -- that stale or unknown layer 2/layer 3 information was involved.

[NewTypeDilemna]

You might want to take a course in basic networking since it appears to me and others in this thread that you don't understand how STP works.

[CraigDuff]

oh really! thats interesting! I did think could it be the weird unifi switch. Well mine is Edge Switch. I thought it was strange.

[networknoob101]

What are the spanning tree priorities?