Disable Jumbo frames on a switch

[Black Ninja]

Perhaps this is easy question for network specialist ,but is out of my knowledge and I couldn't find clear answer anywhere the net:

I don't use jumbo frames on my switch for the moment(so non of my clients are sending jumbo frames). My switch also has an option to enable or disable jumbo frames (managed switch) and I would really like to know what difference does it make if it's enabled or disabled on the switch ?


P.S. My initial understanding was: Just keep it enabled , it won't harm, if nobody is sending jumbo frames it won't matter if it's enabled or disabled and if later decide to isolate few clients in their own vlan with jumbo will be easier. (no need to enable and reboot the switch to make it work), but I don't think is that simple. They won't put an options enable/disable if it could be just enabled all the time and let the end clients set the frames.

 

[dlavigne]

Did you find a clear answer?

 

[Black Ninja]

No, unfortunately. I guess I am asking a tough (but very important) questions that usually goes unanswered.

 

[Black Ninja]

Are you struggling with the same question ?

 

[millst]

Your analysis is fine. You might want to disable jumbo frames at the switch if you have any devices that handle them poorly (crashes, drops off network, etc.). It would also reduce network congestion by dropping any packets that cannot be processed by the destination (as none of them have jumbo enabled).

-tm

 

[Black Ninja]

I have no device(at the moment) that is configured to use jumbo frames. So nobody is sending jumbo frames from the clients. But the question is: If jumbo is enable or disabled on switch how that will effect anything ?!

If there is no harm to leave them enable on switch and just control end devices (not to send jumbo frames) then why would even be an option to disable them on the switch ?!

P.S. Does it create large buffers on switch , or something .... I don't know , but I know you need to Reboot the switch if you make this change on a switch. And that sounds like a big deal since you don't need to reboot the switch for almost nothing else you do with ?!

 

[Black Ninja]

The reason why I am trying to understand the implications on the switch side , despite not using jumbo right know so I could just have them disabled on the switch and that's it:

Is that I consider in the future to create a vlan with few devices using jumbo just between each other while others in the main Vlan are using regular frames set by end devices.

 

[acp]

The reason why I am trying to understand the implications on the switch side , despite not using jumbo right know so I could just have them disabled on the switch and that's it:

Is that I consider in the future to create a vlan with few devices using jumbo just between each other while others in the main Vlan are using regular frames set by end devices.

It is really not a switch issue but a client one. Turning it on simply allows jumbo frames to be sent through the switch. The end clients still need to support it. If turned off and a client sends a jumbo frames the switch will drop the packet as it is invalid.

The problem you will more likely see if server a has jumbo frames enabled and client c network driver is buggy, you may see lots of weird issues that will drive you batty.

It's more how much do you trust the people writing your network drivers. ;)



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[Black Ninja]

So what you are saying is, that the only reason to disable jumbo on switch is to prevent if a client went "crazy" and start sending jumbo to others and disrupt the network ? I don't know what is the likelihood of this to happen, but it could be the case.

I know that if this was a non-managed switch and it support jumbo frames, this means that jumbo will be permanently enabled , since you can't configure the switch. (being non-smart switch).

Am I wrong in my understanding ?

 

[acp]

So what you are saying is, that the only reason to disable jumbo on switch is to prevent if a client went "crazy" and start sending jumbo to others and disrupt the network ? I don't know what is the likelihood of this to happen, but it could be the case.

Usually jumbo frames are off on managed switches. Jumbo frames have to be explicitly turned on at the OS (network driver). I'm not aware of any os where jumbo frames being on is default.

I know that if this was a non-managed switch and it support jumbo frames, this means that jumbo will be permanently enabled , since you can't configure the switch. (being non-smart switch).

Am I wrong in my understanding ?

No. I think you get it.

Use of jumbo frames are limited. In theory you would have reduced overhead using 9k frame sizes instead of the 1.5k standard. But it gets really fun when you have to fragment crossing over to another network and you lose what ever you gained. This is it course depended on your device supporting the, 9k size. The standard that isn't. Lol



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[Black Ninja]

On managed switch, my dell 5524 it's disable by default , on my Fujitsu xg2000 jumbo was enabled by default. By the way I wouldn't consider jumbo on 1GB network at all. I don't think is worth it.
Anyway, I was talking about UN-managed switch or a dumb switch. Those 5-8 port switches you buy for $40 that support jumbo frames. My point was: since you can't manage these switches they must have the jumbo option always enabled on them.(I am talking about just the switch itself)

 

[millst]

I already gave you two reasons for disabling jumbo frames. Of course, they only apply if a client is somehow sending jumbo frames.

Yes, if the switch supports jumbo and it has no interface, then it must be always enabled. Of course, some switches don't even support jumbo.

Honestly, I think you're overthinking the whole thing. It likely makes no significant difference whatsoever. You'll only have problems (obvious problems) when a client is using jumbo and the rest of the network isn't.

-tm

 

[Black Ninja]

I am just trying to understand the implications of enabling or disabling jumbo frames on the switch to avoid the problems.

You'll only have problems (obvious problems) when a client is using jumbo and the rest of the network isn't.

Nobody is saying or doing that.

Thanks for the input, you have a valid points.

P.S. I've been told before that I overthink things, but I just don't believe in those things. I don't believe you can be "too carefully" or "too knowledgeable" that could harm. Most reasons for disasters are from not thinking enough what you are doing , or knowing enough:).

 

[millst]

From what I've seen, the consensus is to disable jumbo frames all around in order to avoid problems (if you really need more bandwidth, go 10GBE).

Yep, always good to understand the pros/cons of things, but this isn't worth a ton of your time IMO.

-tm

 

[Black Ninja]

As I mention I am not even considering jumbo frames on 1Gb network. I am considering jumbo on 10Gb switch on separate vlan. So on 1Gb switch disable jumbo (default) for all 1Gb clients, and enable jumbo on 10Gb switch(default) for jumbo Vlans and non jumbo.

 

[acp]

As I mention I am not even considering jumbo frames on 1Gb network. I am considering jumbo on 10Gb switch on separate vlan. So on 1Gb switch disable jumbo (default) for all 1Gb clients, and enable jumbo on 10Gb switch(default) for jumbo Vlans and non jumbo.

Just remember a lan isn't defined by it's speed but by it broadcast domain. As long as each segment (1g and 10gig) are separated onto two different broadcast domain then you will be good. Using vlans is one way. Using two different switches will also work. It all depends on what your switch(s) supports.

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[Black Ninja]

Just remember a lan isn't defined by it's speed but by it broadcast domain. As long as each segment (1g and 10gig) are separated onto two different broadcast domain then you will be good. Using vlans is one way. Using two different switches will also work. It all depends on what your switch(s) supports.

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Of course. Right now I have my 1Gb switch connected to my 10Gb switch in the same broadcast domain and no jumbo is used anywhere. But I am considering to create another vlan ( isolated broadcast domain from main)(on 10Gb switch) in which I will use the jumbo frames.

In order to do that I need to enable jumbo frames on 10Gb switch (it doesn't have per port option) on the whole switch.

So my original concern was: Will it hurt if jumbo was enabled on the switch but never actually use it ? Meaning - no client was configured to send jumbo frames, but it was enabled on the switch ?

 

[Black Ninja]

Nothing I hate more that reboots (actually crashes is worst). And enabling jumbo frames is one of very few features that requires switch reboot, so I want to make sure that I understand well the implications of having it enabled or disabled(on switch) so whatever I decided to do in a future (like create new vlan with jumbo for storage network only) I don't have to reboot ever.

 

[acp]

Nothing I hate more that reboots (actually crashes is worst). And enabling jumbo frames is one of very few features that requires switch reboot, so I want to make sure that I understand well the implications of having it enabled or disabled(on switch) so whatever I decided to do in a future (like create new vlan with jumbo for storage network only) I don't have to reboot ever.

I think you are over thinking it. If you want to be safe, don't turn on jumbo frames. You will need to validate that jumbo frames are working to what ever specifications you have for your environment. If it doesn't meet it you or have issues you will need to roll back. Otherwise build a parallel environment where you can test without impacting prod. Otherwise you test in prod.

I had previously had jumbo frames turned on. I never had issues that I could trace jumbo frames. I decided it wasn't with the hassle so I never used them. I never bother to turn it off. I upgrade to a newer switch and never bother to turn on jumbo frames. I went with 10gig. Now the network is not the bottleneck. YMMV.



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[Black Ninja]

If you have SAN network on 10Gb , would you go without jumbo ?