Make the secondary interconnect switch the primary interconnect

Procedure for making the secondary ThinkAgile CP interconnect switch into the primary interconnect.

Attention:

You have between 6 and 12 hours to fix the primary interconnect before you notice network connectivity problems, as that is the default lease time of the DHCP server. If you cannot replace the interconnect or DHCP server within 6 to 12 hours, you should attempt to make existing DHCP users static IPs.

Important:

This procedure can be performed only under supervision of or with help from Lenovo Support.

Execution: On hardware only

Performed by: Lenovo Support

Background: Dual interconnect configuration (DS-V3) is active-active. A DHCP server runs on both interconnect switches, and the DHCP lease file is synchronized between the two interconnect. In the event that the primary interconnect switch goes down, the DHCP server on the secondary interconnect begins to service IP requests.

Attention:
  • This only works on the Hypervisor Network. DHCP High Availability does not function on the Management Network.

  • This procedure requires physical intervention on the hardware.

Note:

Ensure that the primary interconnect is shut down when running these steps. Having two DHCP servers in split-brain configuration causes severe disruptions on the stack network.

To make the secondary interconnect switch into the primary interconnect, follow these steps:

  1. (Optional) If the primary interconnect is not shut down, sign in to the primary interconnect in Support Mode or, if at the data center, using a method provided by the manufacturer. The username is admin and the password is the one you set during installation.
  2. (Optional) If the primary interconnect is not shut down, run the following commands on the primary interconnect to disable the DHCP service:

    > sudo service isc-dhcp-server stop

    > sudo service isc-dhcp-server disable

  3. Sign into the second interconnect using the same procedure.
    1. Edit /etc/tacp/tacp_switch_resource.sh with the hypervisor network settings (DHCP_RANGE_START, DHCP_RANGE_END, DHCP_ROUTER_IP, DHCP_NETMASK, PRIMARY_DNS, SECONDARY_DNS) from the primary interconnect.
    2. Copy the backed-up lease database /var/lib/dhcp/dhcpd.leases from the primary interconnect to the corresponding location on the secondary interconnect, if available.
      Note:

      If the backed-up lease database is not available, you need to configure the secondary interconnect as new. ThinkAgile Advantage assists you with this procedure.

    3. Run the following command to create /etc/dhcp/vlan-mgmt.conf with the hardware management network settings (BMC_ DHCP_START, BMC_DHCP_END, BMC_ROUTER_IP, BMC_PREFIX) from the primary interconnect.

      > sudo /usr/share/tacp/reset_bmc_network.sh

  4. If you were unable to copy /etc/dhcp/dhcp-failover.conf from the primary interconnect, create it with the following content.
    failover peer "failover-partner" {
          primary;
          address 100.64.253.1;
          port 647;
          peer address 100.64.253.2;
          peer port 647;
          max-response-delay 60;
          max-unacked-updates 10;
          auto-partner-down 1;
          mclt 120;
          split 255;
          load balance max seconds 3;
       } 
    
  5. Disconnect the hardware management network cable from the former primary interconnect and connect it to the current primary (former secondary) interconnect.
    Figure 1. Recabling management switch from primary to secondary interconnect
    Diagram of cabling from the hardware management network to the interconnects
  6. Start the DHCP server in the new primary interconnect with the following command:

    > sudo service isc-dhcp-server start