Connection speed

[tech_gs123]

Hi Group,

Below is our current setup

1/F: Floor switch cisco WS-C2960G-24TC-L

This is part of a result from show interface status

Gi0/2     staff              connected    10         a-full  a-100 10/100/1000BaseTX

Gi0/3     staff              connected    10         a-full a-1000 10/100/1000BaseTX

Gi0/4     staff              connected    10         a-full  a-100 10/100/1000BaseTX

Gi0/5     staff              connected    10         a-full a-1000 10/100/1000BaseTX

Gi0/21                       connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/22                       connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/23                       connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/24                       connected    trunk      a-full a-1000 10/100/1000BaseTX

Po1                          connected    trunk      a-full a-1000

So port 2 and 4 have maximum speed of 100, port 2 connects to a printer and port 4 connect to an old desktop, port 3 connects to a new laptop, port 5 connects to a new desktop.

Can you please help me to clarify the following:

Connection between port 3 to port 2 is 100?

Connection between port 3 to port 5 is 1000?

In other word, which will happen if I plug slow speed device in the switch? will it only affect connection to that device or the speed of the whole network will slow down?

port 21-24 is trunk, they are connected to 2/F core switch, does it mean that, in theory, i have 4G connection between 1/F switch to 2/F core switch?

2/F:

Core Switch: cisco WS-C3560G-24TS

This is result text from show interface status

Core_SW_2F>show interface status

Port      Name               Status       Vlan       Duplex  Speed Type

Gi0/1                        connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/2                        connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/3                        connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/4                        connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/5                        connected    10         a-full a-1000 10/100/1000BaseTX

Gi0/6                        connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/7                        connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/8                        connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/9                        connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/10                       connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/11                       connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/12                       connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/13                       connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/14                       connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/15                       connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/16                       connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/17                       connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/18                       connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/19                       connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/20                       connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/21                       connected    10         a-half  a-100 10/100/1000BaseTX

Gi0/22                       connected    10         a-full a-1000 10/100/1000BaseTX

Gi0/23                       connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/24                       connected    trunk      a-full a-1000 10/100/1000BaseTX

Gi0/25                       notconnect   10           auto   auto Not Present

Gi0/26                       notconnect   1            auto   auto Not Present

Gi0/27                       notconnect   1            auto   auto Not Present

Gi0/28                       notconnect   1            auto   auto Not Present

Po1       connect to SW_2F_A connected    trunk      a-full a-1000

Po2       connect to SW_2F_B connected    trunk      a-full a-1000

Po3       connect to SW_1F   connected    trunk      a-full a-1000

Po4       connect to SW_3F   connected    trunk      a-full a-1000

Po5       connect to SW_4F   connected    trunk      a-full a-1000

Po6       WLC                connected    trunk      a-full a-1000

I am concern about port 21, it connects to an old server, would it make any improvement in term of overall core switch speed if I move the old server to another floor switch?

I am happy to provide other details if needed

Many thanks in advance

Dixon

[Vivek Ganapathi]

Hello Dixon,

The interface speed is specific to the port & not for the entire switch.

1/F: Floor switch cisco WS-C2960G-24TC-L

1) No, interface speed for Port 3 is 1000 & Port 2 is 100 Mbps. I understand your concern, you feel that if Port 3 talks to Port 2 there would be congestion? The answer is no. Firstly, you can't pump at such high line rates. Secondly, if data is pumped at such faster rates, the OS running on the Port 2 has intelligence enough to inform the device on Port 3 to reduce the throughput at which data is being pumped. So, nothing to worry.

2) The above answers you second question as well.

Overall, if you were to plug in a old / slow device into a switch, then it's the device connected to it suffering Not at all the switch.

Hope i tried to keep it simple & tried to explain as much as i know

Vivek.

[tech_gs123]

Thanks Vivek for your quick reply. It makes a lot of sense. How's about trunking? is it correct to assume that in theory, the connection between 1/F and core switch is 4 gigabit ?

Thanks again

Dixon

[Vivek Ganapathi]

Yes, its 4 Gbps.

[Joseph W. Doherty]

Disclaimer

The     Author of this posting offers the information contained within this     posting without consideration and with the reader's understanding  that    there's no implied or expressed suitability or fitness for any   purpose.   Information provided is for informational purposes only and   should not   be construed as rendering professional advice of any kind.   Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In     no event shall Author be liable for any damages whatsoever   (including,   without limitation, damages for loss of use, data or   profit) arising  out  of the use or inability to use the posting's   information even if  Author  has been advised of the possibility of  such  damage.

Posting

First, your question about ports 21 to 24 being trunked, doesn't, alone, imply there's more bandwidth.  Trunked ports allow passage of multiple VLANs across them.  In your case, you also have a port channel on that device, "Po1", and assuming it bundles ports 21 to 24, then you do obtain more aggregate bandwidth.  However, a single flow will only use one link, i.e. a single flow would not be able to use more than a gig on those ports.  Multiple flows can use multiple links, but they can also use the same link.  I.e. two flows might use two different links or they might use the same link.

Second, anytime you can transmit faster than you can receive, there's a chance of overrunning the receiver.  So a gig port sending to a FastE port can overrun the latter and such congestion often leads to packet drops.  Everything else being equal, a device sending on a FastE port to a device on a FastE port will probably be "faster" than a device sending on gig port to a device on a FastE port.  However, the difference often isn't extreme, as some (and often most used) network protocols expect, and allow for, this.  (E.g. TCP)

Connecting slow/old devices to a switch, isn't generally a concern, but sometimes where a really fast/busy device is connected can be a concern especially with older switches.  (Older switches commonly didn't have the actual physical performance to process all ports being busy concurrently.)