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in our topology we have our Data Server(Multi Virtual Servers) and Backup Server exist in two different buildings and the current connection between them as below:

enter image description here

Connection explanation:

*1st building:

-Data Server connected to a fiber switch using 1 port-channel of 4x1 gigabit ports -Fiber Switch connected to Core Switch using 2 port-channels of 2x1 gigabit ports

*2nd building:

-Core Switch connected to Fiber Switch using 2 port-channels of 2x1 gigabit ports -Fiber Switch connected to a Backup Server using 1 port-channel of 4x1 gigabit ports

well,this connectivity is not giving more than 1 gbps and it is very less for the amount of data to be transferred.

will we get more bandwidth by changing the connectivity to be as below:

enter image description here

Connection explanation:

*1st building:

-Data Server connected to Core Switch using 2 port-channels of 2x1 gigabit ports

*2nd building: -Core Switch connected to Backup Server using 2 port-channels of 2x1 gigabit ports

Sorry for the long explanation and looking for your help. Regards, Ethem

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2 Answers 2

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I think you're misunderstanding port channels. Any one flow will still be capped at the speed of a single link in the channel. There is a hashing algorithm that decides which link a flow will use. With multiple flows, all the links will be used, so in aggregate, you can get the full bandwidth of the channel, but any one flow will be capped at the bandwidth of a single link, although it may be less because it may need to share that link with other flows.

You do not want a single flow to use more than one link. That will increase out-of-order packet delivery. TCP can handle that, but it will slow processing. UDP cannot handle that, and it will destroy real-time protocols such as VoIP or video.

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  • Thanks Ron.I know that portchannel's bandwidth will not go beyond the bandwidth of it's individual links.
    – Ethem
    Commented Jul 12, 2018 at 13:10
  • currently we have the upper implementation. and the thing is while preparing for my exam ,one of the videos was mentioning about how to fool the server and achieve active/active forwarding on the individual ports as below
    – Ethem
    Commented Jul 12, 2018 at 13:17
  • couldn't add the picture,,but the thing is it was mentioned that using both uplinks are possible at the same time by bonding the downstream switches using stackwise or VSS to get the maximum of the uplinks capacity.is that true? thanks..
    – Ethem
    Commented Jul 12, 2018 at 13:21
  • As I explained in my answer, active/active on multiple links is a bad thing. Your switches will not do that. Some servers have the option, but then you run into a problem that the switch not do it for the receiver, so you would drop half the traffic, anyway.
    – Ron Maupin ♦
    Commented Jul 12, 2018 at 13:21
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Any single flow cannot exceed the bandwidth of a single member link within a port channel, so in your case, a single flow cannot go above 1 Gbps.

If there are multiple flows between the two servers, you may be able to benefit from more than 1 Gbps, if you adjust the load balancing mechanism on the switches to take into account L4 port number (if supported). You would need to do this on the servers as well (again, if supported) and configure the application to use multiple ports. You may then get higher than 1 Gbps aggregate bandwidth

The main issue with both of your topologies above is that you are using multiple port channels on the VSS on either side. In the top diagram, the 4 links connecting the VSS to fibre switch 1 are in two bundles. Same goes for the 4 links connecting to fibre switch 2. Also, in your second diagram, the same is occurring (2 bundles to server 1, two bundles to server 2). This doesn't make best use of the bandwidth as you are providing a looped L2 topology causing STP to go blocking on some of the links. You will find that half the links on the left and half the links on the right are STP blocking, reducing your aggregate throughout to the VSS from 4 Gbps down to 2 Gbps. The VSS acts as a single switch logically to STP. You can bundle all 4 links to fibre switch 1 as one port channel (on both sides), same for fibre switch 2 and same in the second topology. This way you will get the full 4 Gbps (although still limited to 1 Gbps per flow)

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