Mac Address Table、Packet Buffer

[To the ocean]

hi, does anyone know what are the benefits of Mac Address Table、Packet Buffer?
I just know that it's better that the number of Mac Address Table and Packet Buffer is bigger and bigger
but what would these 2 items actually affect?

 

[ColinTaylor]

I suggest you use Google or another search engine for an explanation of these. They are not something that you would normally pay any attention to in a home network.

 

[sfx2000]

I suggest you use Google or another search engine for an explanation of these. They are not something that you would normally pay any attention to in a home network.

I agree...

Going back to OP's question - the MAC address table tracks the MAC addresses of the devices attached to the switch.

Packet Buffers, by default, are sufficient to handle traffic across the switch, and if too small, the switch will start blocking traffic under load.

For home networks - the switch inside the router/AP is sized appropriately, and same goes with unmanaged desktop switches.

It's pretty much transparent, and no need to make any changes, even if it were possible.

hth..

 

[To the ocean]

thx for @ColinTaylor and @sfx2000
I've noticed that you both mention that they're not something important to home network
So on the other side, it's quite important to business network, right?

since if the Packet Buffer is too small, the switch will start blocking traffic under load, which means network speed will slow down.
and if the MAC address table is too small, which means that the fewer MAC addresses of the devices attached to the switch could track.

I think these 2 items are important to a managed switch?

 

[ColinTaylor]

I think these 2 items are important to a managed switch?

Why are you concerned about this? As @sfx2000 said, the hardware manufacturers size these things appropriately for the device in question. So if you have an enterprise switch which is connected to a network with thousands of clients or extremely high throughput it will have a larger MAC table and buffers than a 5-port desktop switch. This has nothing to do with whether the switch is managed or not.

 

[coxhaus]

In a small network probably not important but in a larger network it affects the network speed. If the CAM table is too small the switch will need to broadcast to find the MAC address which slows the network.

The best way to maintain speed in a home network is to use 1 switch so all traffic is processed at backplane speeds with no port speed bottlenecks.

 

[drinkingbird]

thx for @ColinTaylor and @sfx2000
I've noticed that you both mention that they're not something important to home network
So on the other side, it's quite important to business network, right?

since if the Packet Buffer is too small, the switch will start blocking traffic under load, which means network speed will slow down.
and if the MAC address table is too small, which means that the fewer MAC addresses of the devices attached to the switch could track.

I think these 2 items are important to a managed switch?

Even cheap switches support tens of thousands of MAC addresses. It is pretty much 0 concern these days.

Buffers mostly only come into play if there is a bottleneck. A 1G connection with bad wiring that is throughput limited for example. When there is a constant limitation like 1G physical port speed, TCP is very good at detecting congestion and throttling back. But when there is a bad connection and variable packet loss, throughput changes, etc, buffers start to get used. They also get used for UDP when the amount being sent is larger than the port size, but that would start dropping pretty quickly regardless of buffer size.

But buffers can't be sized too large, that would just end up causing a bunch of latency and application issues. Again, its pretty standard across all devices and not something you really need to be concerned with. If you're hitting buffers and they're dropping a lot, you have some other issue going on that you need to fix.

 

[drinkingbird]

In a small network probably not important but in a larger network it affects the network speed. If the CAM table is too small the switch will need to broadcast to find the MAC address which slows the network.

The best way to maintain speed in a home network is to use 1 switch so all traffic is processed at backplane speeds with no port speed bottlenecks.

Switches learn the MAC of connected devices by examining the ethernet frames passing through. Switches are passive devices.

What you're thinking of is when a MAC (or CAM, or hardware) table fills up, the switch essentially becomes a hub and sends the frames for unknown MACs out every port, so yes in that way it is a broadcast, but it isn't broadcasting to learn a MAC, it is just forwarding the traffic blindly until its MAC table has space, then it learns that MAC and no longer has to flood the traffic.

You'd have to daisy chain a lot of switches and have a lot of devices to run into that issue on even a cheap home switch. Not something that ever happens anymore.

In a corporate environment if anyone manages to exceed the MAC table size, they don't know how to design a network. You'd essentially have to have a /16 all in one broadcast domain with no routing.

 

[coxhaus]

Yes. I only know old school.
I can remember when some switches advertised the number MACs supported.
I can also remember making CAM tables bigger in Cisco catalyst 6500 switches.

PS
I want to say the Cisco 6500 ran catalyst code and you had a RSM blade that ran IOS with the routing blade only supporting 2 gig of routed data. But I have slept since then.

 

[drinkingbird]

Yes. I only know old school.
I can remember when some switches advertised the number MACs supported.
I can also remember making CAM tables bigger in Cisco catalyst 6500 switches.

PS
I want to say the Cisco 6500 ran catalyst code and you had a RSM blade that ran IOS with the routing blade only supporting 2 gig of routed data. But I have slept since then.

I worked on hundreds of 6000s and 6500s back in the day. Converted my company's access and distribution tiers from 5000 and 5500s.

On 6500 you could run CATOS on the switch and IOS on the L3 MSFC (hybrid mode) or eventually IOS on the whole thing (native). I believe that started with MSFC-II that you could run native.
Honestly on high port density switches, CATOS was so much easier. IOS requires you to do this "interface range" command to apply a setting to a lot of ports and it was very sensitive to how you typed it, and in a 13 slot chassis got annoying.

I think the 6000 (didn't support the MSFC, L2 only) only ran CATOS, but that may have been updated in later supervisor releases, not sure.

The CAM table thing got defaulted to much larger pretty quickly after the 6k series became popular, I vaguely remember having to set it in our boiler plate config around 2000 but we took it out at some point as the default became larger than what we were setting it to.

"Session 15" to get from the switch into the router module. Those were the days.

You could put a "flexWAN" module in it to run TDM circuits and the like too, same PA line cards from the 7000 series routers. Was a great switch.

Pretty sure even 4 port switches now support like 65,535 MACs or something like that. It is still in the specs but pretty much nobody looks as it is a non-issue these days.