Secondary Virtual dynamic (DHCP) Private IP is getting flushed out in every reboot

Question

Secondary Virtual dynamic (DHCP) Private IP is getting flushed out in every reboot

Rasool SB 0

I am trying to add a secondary virtual dynamic (DHCP) private IP address on azure linux virtual machine using "ifconfig eth0 add 192.168.1.6" and it is successfully added as soon I ran the command (hurray). before running the above command to add secondary virtual IP address inside OS, I have added the secondary virtual IP address through Azure portal followed by the steps (NIC -> IP Configuration -> Add). Here my issue starts, if I reboot the machine, it is getting flushed out (deleted). then again I have to run the same command to add secondary virtual IP to make it available. Am I missing something to update any file ? or to modify any file, so that it will be saved permanently ? Sorry, I am newbie, please bare with my illogical or stupid question if it is :(

Izmir Sadigov 111 Reputation points MVP

2023-04-24T06:16:05.7066667+00:00
If you are using Microsoft Azure for your virtual machines (VMs) and the private IP address assigned via DHCP is getting flushed out in every reboot, there are a few possible reasons and solutions:

Azure VM configuration: In some cases, the Azure VM's configuration settings may cause the DHCP-assigned private IP address to be released upon reboot. Specifically, the "Delete OS disk" option in the VM configuration settings can cause the VM to be reset to its initial state, resulting in the DHCP lease being released. To fix this, ensure that the "Delete OS disk" option is not selected when creating or configuring the VM.

Custom script or startup task: If you have a custom script or startup task configured on the Azure VM that is releasing the DHCP-assigned IP address during boot, you may need to review and modify the script or task to retain the IP address. Make sure that your custom script or startup task is not explicitly releasing or renewing the IP address.

Azure Virtual Network settings: The Virtual Network (VNet) settings in Azure can also impact the DHCP-assigned IP address retention. Specifically, the "Enable IP forwarding" option in the VNet settings can cause the VM's IP address to be released upon reboot. Ensure that the "Enable IP forwarding" option is not selected if you don't require IP forwarding on the VM.

DHCP lease duration: DHCP leases in Azure are typically configured with a default duration of 1 day. If you have a short DHCP lease duration, such as a few minutes or hours, the IP address may expire and be released upon reboot. To fix this, you can try extending the DHCP lease duration to a longer period of time using custom DHCP settings in Azure.

Network security group (NSG) rules: NSG rules in Azure can also impact the retention of DHCP-assigned IP addresses. If you have NSG rules that block DHCP traffic, it can cause the VM to lose its IP address upon reboot. Make sure that your NSG rules are not blocking DHCP traffic and allow the necessary DHCP traffic for IP address assignment.

Virtual machine scale sets: If you are using Azure Virtual Machine Scale Sets (VMSS), the VM instances may be automatically replaced or reconfigured during scale-in or scale-out operations, which can result in the DHCP-assigned IP addresses being released. Make sure that your VMSS settings and scaling policies are configured properly to retain IP addresses during scale-in or scale-out events.
Rasool SB 0 Reputation points

2023-04-24T23:05:42.3433333+00:00

Thank you so much for investing your efforts on my issue/question and apologies for the way I described above question, it seems bit confusing.

The primary ifconfig1 (DHCP) IP address is working perfect and causes no errors, no issues even after rebooting the VMs.

I have 2 DHCP IPs assigned to same NIC (NIC1) on single VM, one is default Primary IP (ifconfig1) 192.168.1.4 and the second IP which is created as "Virtual IP" and the address is 192.168.1.5. Default primary IP address is working perfect and it gives no error. the secondary IP which is created as "Virtual IP address" is not able to ping by default. to solve this issue, I have added the secondary virtual IP address inside Azure customized Linux operating system by following the command "ifconfig eth0 add 192.168.1.5" and it is added successfully and it starts to ping the server with 192.168.1.5.

Here my issue starts, If I reboot the VM by portal or by OS, whatever the command I ran (ifconfig eth0 add 192.168.1.5) to make the server ping through this IP address 192.168.1.5 is getting flushed out. if I run "ifconfig" after reboot, it shows only one IP address and it is default one "192.168.1.4". Azure customized Linux Operating system is resetting the ipconfig file at the time of loading operating system. hence it is getting flushed out.

Kindly help me!

2 answers

Your answer

Rasool SB 0 Reputation points

2023-04-24T23:05:42.3433333+00:00

Thank you so much for investing your efforts on my issue/question and apologies for the way I described above question, it seems bit confusing.

The primary ifconfig1 (DHCP) IP address is working perfect and causes no errors, no issues even after rebooting the VMs.

I have 2 DHCP IPs assigned to same NIC (NIC1) on single VM, one is default Primary IP (ifconfig1) 192.168.1.4 and the second IP which is created as "Virtual IP" and the address is 192.168.1.5. Default primary IP address is working perfect and it gives no error. the secondary IP which is created as "Virtual IP address" is not able to ping by default. to solve this issue, I have added the secondary virtual IP address inside Azure customized Linux operating system by following the command "ifconfig eth0 add 192.168.1.5" and it is added successfully and it starts to ping the server with 192.168.1.5.

Here my issue starts, If I reboot the VM by portal or by OS, whatever the command I ran (ifconfig eth0 add 192.168.1.5) to make the server ping through this IP address 192.168.1.5 is getting flushed out. if I run "ifconfig" after reboot, it shows only one IP address and it is default one "192.168.1.4". Azure customized Linux Operating system is resetting the ipconfig file at the time of loading operating system. hence it is getting flushed out.

Kindly help me!

Answer 1

Rasool SB 0

My above described issue has been resolved, by running below commands. Instead of using ifconfig, please use nmcli. Commands I used to solve my issue is: 1. nmcli con add con-name eth0 type ethernet +ipv4.addresses 192.168.1.5/26 2. nmcli con up eth0

Answer 2

@Rasool SB I'm glad that you were able to resolve your issue and thank you for posting your solution so that others experiencing the same thing can easily reference this!

Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others ", I'll repost your solution in case you'd like to "Accept " the answer. Accepted answers show up at the top, resulting in improved discoverability for others.

Issue: Secondary Virtual dynamic (DHCP) Private IP is getting flushed out in every reboot.

If I reboot the VM by portal or by OS, whatever the command I ran (ifconfig eth0 add 192.168.1.5) to make the server ping through this IP address 192.168.1.5 is getting flushed out. if I run "ifconfig" after reboot, it shows only one IP address and it is default one "192.168.1.4". Azure customized Linux Operating system is resetting the ipconfig file at the time of loading operating system. hence it is getting flushed out.

Solution: Instead of using ifconfig, please use nmcli. Commands I used to solve my issue are:

1. nmcli con add con-name eth0 type ethernet +ipv4.addresses 192.168.1.5/26

2. nmcli con up eth0

If you have further questions, please let us know in the comments how we can assist. We are here to help you and strive to make your experience better and greatly value your feedback.

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Secondary Virtual dynamic (DHCP) Private IP is getting flushed out in every reboot

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