IBM Support

Virtual machine with multiple NICs is not reachable after you reboot the virtual machine

Troubleshooting


Problem

A virtual machine which has multiple NICs added through "add NIC" add-on of the pattern builder user interface, is not reachable after its first reboot. This problem occurs when a virtual machine is created with default Linux OS image "IBM OS image for Red Hat Linux Systems", which has more than two NICs that are added through "add NIC" add-on of pattern builder user interface.

Symptom

The virtual machine is neither accessible through SSH nor manageable from Platform System Manager.

Diagnosing The Problem

Verify the problem with the following steps:
  1. Log in to the virtual machine through SSH.
  2. Run the following command and record the output:
    ifconfig -a
  3. Reboot the virtual machine.
  4. After reboot, run the following command and record the output:
    ifconfig -a
  5. Compare the IP to MAC address (HWaddr) mappings before and after the virtual machine reboot.
  6. The result is that the IP to MAC address mappings get shuffled after reboot, due to which virtual machine connectivity is lost.

Resolving The Problem

Resolution:
The issue occurs due to a restriction with VMXNET3 virtual network adapter, which currently supports only two user add-on NICs (in addition to the default management and data NICs present in the image) .

See the following Knowledge Center topics:
https://www.ibm.com/support/knowledgecenter/SSCR9A_2.3.1.0/doc/iwd/pct_manage_cat_vi.html
https://www.ibm.com/support/knowledgecenter/SSCR9A_2.3.1.0/doc/iwd/aoc_addonsov.html

The following workaround can be used to resolve the problem:
  • Log in to the virtual machine and run the following commands, which makes the NIC names and the order of the NICs consistent:
    vi etc/default/grub
    net.ifname=1
    :wq
    grub2-mkconfig -o /boot/grub2/grub.cfg
    service NetworkManager start
    nmcli connection add type ethernet mac "<eth0 mac address>" ifname "eth0"

These steps must be run for all the network interfaces of the virtual machine.

Document Location

Worldwide

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Product Synonym

IBM Cloud Pak System

Document Information

Modified date:
06 May 2020

UID

ibm11115025

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