Deployment and test steps to avoid a network loop

When deploying the X10G in a VLAN with high availability, to avoid introducing a network loop, configure the devices and test the configuration in careful steps. Include a network engineer in the configuration and testing of the switches.

Before making any changes, ensure that you have accurate documentation of the current network configuration, as well as the planned, finished configuration.

You should know:

  1. The active and planned STP protocols.
  2. The active and planned STP priority of each switch.
Supported STP protocols include:
  • RSTP - The default protocol on the X10G Dell M6220 switches.
  • MSTP - Document the STP priority on each VLAN, including the STP management VLAN. Know the STP priority of each VLAN allowed through the trunk interface.
  • PVST* - Document the STP priority on each VLAN, including the STP management VLAN, typically VLAN 1. *If you plan to deploy PVST, it is recommended that you contact Technical Support to review planning and configuration steps.

Recommended configuration and deployment steps.

Steps

  1. Ensure that the external switch has a lower priority number than the X10G switches (lower than the Dell M6220 default setting).
    1. Pre-8.0: the default setting is 32768 on both M6220 switches and the blades.
    2. 8.0 and higher: the default setting is 57344 on the switches and 61440 on the blades.
  2. Ensure that all X10G blade switch interfaces are configured with STP enabled and have root guard enabled. Switch interfaces Gi1/0/1-16 should have a configuration similar to:

  3. Until STP and networking are confirmed working, shut down all but one of the blade interfaces. This limits the amount of network loop traffic generated if something goes wrong.
  4. Connect only one 10Gb interface at a time to the external switch. Make sure that the other M6220 10Gb interface is either physically disconnected or in an admin shutdown state. This prevents the possibility of a network loop while STP testing is performed.
  5. Configure the 10Gb trunk interface on both the external switch and the M6220 switch, and bring them up.

    If all VLANs are not being allowed in the configuration, it is recommended to manually add VLAN 1 to the allowed VLANs on the trunk on the external port. VLAN 1 is typically the management non-tagged VLAN that carries STP BPDU traffic between the switches. The M6220 automatically detects that VLAN 1 has been added.

  6. When the trunk is up, test that STP is working correctly.
    1. Log on to the M6220 and run:
      show spanning-tree detail

      If spanning tree is working correctly:

      1. The external switch root’s MAC address is listed in the ROOT ID Address
      2. One of the 10Gb interfaces is listed as the Root Port.

    2. Check to see if BPDU packets are being sent and received on the uplink port to the external switch. To do this, after running the “show spanning-tree detail” command, scroll down to the Ten Gig Ethernet interfaces such as Te1/2/1 or Te1/2/2. In the screen capture you can see that BPDU packets are being sent and received. The interface is also designated as the “root” and is in a “forwarding” state.

    3. Use “ping” and “ssh” (if enabled on the blade) to test connectivity to the enabled blade.

      If after running show spanning-tree detail you see the message “This Switch is the Root”, there is a configuration problem. Do not proceed to the next step until you can get the trunk and STP up and confirmed talking with BPDU packets.

  7. After the first switch is configured and confirmed to be using STP correctly, shut down that 10Gb interface and bring up the other switch’s 10Gb interface. Follow the same steps as above until networking and STP function are confirmed working.
  8. Confirm that STP functionality is working all the way through to the blade’s Open Vswitch (OVS). To do this safely, with one of the switches up, connect with “ping” to the blade. Then shut down the switch port that is up and bring up the other switch port. If this test is successful, you know that STP is working all the way through to the blade.
  9. It is now safe to enable both Dell 6220 switch uplink ports to the switches. Start with only one blade interface enabled.
  10. Monitor CPU traffic on the switches. If there are any heavy spikes, immediately shut down one of the uplink interfaces.