Question about gigabit uplink

[jakesmith]

Question/Verification

If I have a 100mbit switch with 1 - 1gigabit uplink that connects to another switch. Does the gigabit uplink act as a really big water pipe with smaller pipes connected(the 100meg lines) to it?

So I guess in a perfect world you could have 10 100mbit devices transferring at full speed over the gigabit line?

If that is the case, does the switch convert the 100mbit packets to gigabit packages? Because if I recall gigabit packets are made up differently.

Can anyone clarify?

 

[john3850]

Look up the requirements of a gig lan first.

 

[seepy83]

Question/Verification

If I have a 100mbit switch with 1 - 1gigabit uplink that connects to another switch. Does the gigabit uplink act as a really big water pipe with smaller pipes connected(the 100meg lines) to it?

So I guess in a perfect world you could have 10 100mbit devices transferring at full speed over the gigabit line?

Yes.

If that is the case, does the switch convert the 100mbit packets to gigabit packages? Because if I recall gigabit packets are made up differently.

I'm pretty sure the packets (Layer 3) will still be formed like any other IPv4 packet. However, gigabit does allow for Jumbo Frames (Layer 2) as long as the switch supports it. One of the more seasoned networking guys can correct me if I'm wrong, but I assume that it is possible for the switch to use jumbo frames on the gigabit interface even though they are not used on the fast ethernet ports.

Edit: I'm not sure if Jumbo Frames on the uplink port would provide any increased performance in the switching infrastructure as a whole when all of the other ports are standard sized frames. Hopefully someone else weighs in...

 

[drebo]

You want your MTU to be the same throughout your entire switched LAN. If it's not, you'll get fragmentation and potentially other issues as well.

All things default, the gigabit uplink will function at gigabit speeds if connected to a gigabit port on another switch. Don't screw around with your MTU unless you really need to (hint: you don't).

 

[jakesmith]

All things default, the gigabit uplink will function at gigabit speeds if connected to a gigabit port on another switch

Right, I get that, but if all the other ports on the switch are 100meg with 100meg computers attached to them. Does the gig uplink speed things up and like I said allow the individual 100meg computers to transmit faster as there will be less congestion?

 

[Lifted]

the 100mb nodes will communicate at 100mb. if the switch is linked to another switch at gb, you will have up to 1,000mb connectivity between the switches. if a node on switch A needs to communicate with a node on switch B, they will be limited to 100mb as each node only supports 100mb. With the 1gb link between the switches, you can have 10 nodes communicating at 100mb between the two switches, or 20 nodes communicating at 50mb, etc. It never works out so perfectly, and you have other limitations to worry about in high traffic environments (backplane/pps performance) but this is the general idea.

 

[jakesmith]

the 100mb nodes will communicate at 100mb. if the switch is linked to another switch at gb, you will have up to 1,000mb connectivity between the switches. if a node on switch A needs to communicate with a node on switch B, they will be limited to 100mb as each node only supports 100mb. With the 1gb link between the switches, you can have 10 nodes communicating at 100mb between the two switches, or 20 nodes communicating at 50mb, etc. It never works out so perfectly, and you have other limitations to worry about in high traffic environments (backplane/pps performance) but this is the general idea.

Thats what I was looking for. Thanks everyone