Please Explain about Snake test for Layer-2 switching test

Routing & Switching Switching
1

Could you explain how the switch handles L2 traffics by using all ports internally and externally?

Please refer the above the url for the topology setup.

I assume that the switch knows the two traffic generators’ MAC addresses.

My question is how the switch delivers the L2 traffics from port1 to port 8 through all the ports.

Thanks,
Whijoon,

2

Hi Whijoon,

I think you refer to this document?

They run a throughput test with a traffic generator and instead of using just two ports, they use all ports to check the maximum throughput of the switch. Here’s what they do:

  • Port 1 and 2 are in VLAN 1
  • Port 3 and 4 are in VLAN 2
  • Port 5 and 6 are in VLAN 3
  • Port 7 and 8 are in VLAN 4

Port 1 receives incoming traffic from the traffic generator, port 8 sends it back to the traffic generator. Port 2+3, 4+5, 6+7 are connected with a cable. By forwarding the traffic like this, you don’t just test the throughput of 1-2 ports but since the switch has to use all ports, you can test the actual throughput of the backplane.

Rene

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3

Dear Rene,

I have a little question ;

  • Why traffic from Port 2 can sent through Port 3 when they have different VLAN?
  • Each port can config access mode?

And in your answer is test at layer 2 if I should test in layer 3, each port be configured IP address /32 ? and config routing every subnet I don’t understand how to use different vrf for forward traffic.

Thank you.
Amiie

4

Hello Nttiya

In a Layer 2 snake test, each port is an access port. That means that the physical connection between port 2 and port 3 doesn’t require that the VLANs ports 2 and 3 be the same.

Think about two switches connected to each other via an access port. There is no requirement that the VLAN on both ends of such a link be the same. Only trunk ports require that the allowed VLANs on both ends be the same. That is why ports 2 and 3 can be on different VLANs, even though they’re connected.

This however would be unusual in a production network topology, as keeping VLAN IDs consistent is important to avoid misconfigurations. But for the snake test, it will work just fine.

If you test at layer 3, then you would create multiple VRFs, one for each pair of ports. VRFs are kind of like VLANs for routers. Each VRF is a different routing domain. If you configure each pair on a different VRF, and you configure routing appropriately, you can route traffic over the same path as in the Layer 2 test.

To find out more about VRFs, take a look at this lesson:

I hope this has been helpful!

Laz

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