How to determine the max throughput of a Layer 3 device

[Hawk]

We have to upgrade a 2 Gbps circuit to a 4 Gbps circuit and have a 48 port 3750x running layer 3 on both sides of the circuit.  I am struggling to find an explicit reference anywhere showing what the max layer 3 throughput is for this device.  Can anyone guide me in the right path?

[ADP_89]

Hello,

If you want a perfect reading of this value you need to actually test it with a traffic generator as it really depends on the environment and the features you enabled on the configuration. Having said that the switch has backplane fabric capacity of 160Gbps and a forwarding rate of more that 100Mpps. Routing is done completely in hardware so I wouldn't be concerned between an upgrade from 2 to 4Gbps.

HTH,

ADP

[Hawk]

Thanks for the feedback.  Could you explain how you determined that upgrading from 2Gbps to 4Gbps would be ok?  From what I understand the 160 GB backplane is not a determining factor in and of itself to confirm the max layer 3 throughput.

[ADP_89]

Considering that an IP packet can be from 64 to 1500 byte and that the switch can forward more than 100 Milions of packets you can multiply 100 milions for the smallest packet which is 64byte and you will get 6,4GBps so 51,2 Gbps. This is just a brief calculation, you should really consider what type of traffic will go through that link and how big the packets are (if there are a lot of tcp.ack packets the average will drop). In my experience across several datacenters I managed to trakc down the Gbps:Mpps ratio which is:

6:1 for outbound traffic (obviously here packets are bigger as they transport the web and other app data)

3:1 for inbound traffic (here you normally get a bunch of queries/acks)

If you want to be sure that your switch can support that traffic I suggest you to create 2 new vlans/svis and run iperf3 between a few test hosts that you will put in those new vlans.

HTH,

ADP