03-06-2012 06:45 PM - edited 03-07-2019 05:23 AM
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
03-06-2012 09:21 PM
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.
03-06-2012 10:05 PM
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
03-07-2012 06:17 AM
Yes, its 4 Gbps.
03-07-2012 08:09 AM
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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.)
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