I want to stress all ports on a SN3700 switch with iPerf. I want to force the traffic to go through each port, so port 1 to port 2, port 2 to port 3, port 3 to port 4, etc.

The switch is running Cumulus Linux 5.6. I have a support unit, Unit 1, connected to port 1, and a support unit, Unit 2, connected to port 32. There are direct-attach cables connecting all other ports, so port 2 is connected to port 3, port 4 to port 5, etc. I am running the iPerf client on Unit 1 (connected to port 1) and the iPerf server on Unit 2 (connected to port 32).

I'm not sure I have the VLANs configured correctly. I have swp1 and swp2 in VLAN5, swp3 and swp4 in VLAN6, etc.

I've done this on a SN3700 with Onyx OS, and on a Ruckus switch with FastIron, but I don't believe I have the correct configuration for this SN3700 running Cumulus Linux 5.6.

Example contents of the /etc/network/interfaces file:

auto swp1
iface swp1

auto swp2
iface swp2

. . .

auto swp32
iface swp32

auto br_vlan5
iface br_vlan5
   bridge-ports swp1 swp2
   bridge-vlan-aware no
   bridge_stp off

auto br_vlan6
iface br_vlan6
   bridge-ports swp3 swp4
   bridge-vlan-aware no
   bridge_stp off

. . .

auto br_vlan20
iface br_vlan20
   bridge-ports swp31 swp32
   bridge-vlan-aware no
   bridge_stp off

I expected to be able to pass traffic from Unit 1 through each switch port sequentially (Unit 1 in to port 1, (internally "routed") to port 2, out to port 3, (internally "routed") to port 4, ..., out from port 32 to Unit 2). I can't even ping Unit 2 from Unit 1.

What am I missing? TIA!

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    – Zac67
    Jan 1 at 10:54

1 Answer 1


You can't tell a switch for forward traffic to a specific port but don't egress that port and go somewhere else. But you can use VLANs to provide the desired connectivity to chain switch ports. Most likely a useless exercise but for what it's worth:

  1. create half as many VLANs as you've got ports to test
  2. disable RSTP/MSTP/RPVST on the ports
  3. configure ports 1 and 2 with VLAN 1 untagged
  4. configure ports 3 and 4 with VLAN 2 untagged
  5. repeat until you run out of ports
  6. using patch cables, connect ports 2 and 3, 4 and 5, 6 and 7, and so on
  7. connect test hosts to ports 1 and the last one

I've used this kind of setup for a disproof of concept once.

  • I already have things physically set up that way. I need the configuration programming for the VLANs, as I don't think what I have (in the /etc/network/interfaces file) is correct. Nov 27, 2023 at 20:04

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