Connecting 2 switch interfaces with different speeds

[chamaraw07]

Hi Guys

really appriciate if anyone coulde help me with below ,

if two switches are connected with one switch having a 1Gbps port and the other with 10 Gbps port then would the switch with 1 Gbps port drop packets ? or would it queue packets?

is this whats call oversubscrption?

if the switch port with 1 Gbps has a throughtput of only 1 Gbps then what would if traffic exceeds

1 Gbps , for example if it receives 2 Gbps?

thanks

Cham

[Mark Malone]

Hi

if you have a speed miss match you could end up with droppd packets , you could end up in half duplex which will cause you issues between the devices collisions dropped packets etc , its good parctice to have speed/duplex match whether its auto or hardcoded they should at least be the same

You have a hold queue in routers and switches interfaces if that fills up you can end up discarding packet as the interface is oversubscribed , it can happen quite easily , having a file or blade server connected to an access switch or low level line card you will see it pretty quick

[chamaraw07]

Thanks Mark

does the switch port hold every packet it receives in the queue first and then send to switch processor?

or does it  send all packets directly to switch processor as soon as a packet is received on a port and  only queue packets if the switch processor is busy?

Thanks

[Mark Malone]

It should be priocessed straight away unless the interface is being hammered then it will be queued , if the queues/buffers fill thats it packets will start dropping after that , you can increase the queues but you can cause latency doing this too

[chamaraw07]

Thanks Mark

so once a packet is received on an interface and if the switch processor is overwhelmed then the packet would be put in the input queue untill the switch processor is ready to process that packet ?

if thats the case what is the purpose of the output queue ?, im assuming packets come to output queue after they are being processed by the switch CPU