Contradictory information

[carlos-quintero]

The page "How network security groups filter network traffic", section "Inbound traffic" (https://learn.microsoft.com/en-us/azure/virtual-network/network-security-group-how-it-works#inbound-traffic) states:

"VM4: Traffic is blocked to VM4, because a network security group isn't associated to Subnet3, or the network interface in the virtual machine. All network traffic is blocked through a subnet and network interface if they don't have a network security group associated to them."

That information is in contradiction with these other four resources that state that if a VM with a public IP

1. Is in a subnet without a network security group

and:

2. It's network interface card doesn't have a network security group either

then:

All inbound traffic is allowed in all ports (not blocked):

1. Diagnose a virtual machine network traffic filter problem
   https://learn.microsoft.com/en-us/azure/virtual-network/diagnose-network-traffic-filter-problem
   "If there are no NSGs associated with the network interface or subnet, and you have a public IP address assigned to a VM, all ports are open for inbound access from and outbound access to anywhere. If the VM has a public IP address, we recommend applying an NSG to the subnet the network interface."

2. How network security groups filter network traffic
   https://learn.microsoft.com/en-us/training/modules/filter-network-traffic-network-security-group-using-azure-portal/4-create-network-security-group
   "VM4: Traffic is allowed to VM4, because a network security group isn't associated to Subnet 3, or the network interface in the virtual machine. All network traffic is allowed through a subnet and network interface if they don't have a network security group associated to them."

3. Determine network security group effective rules
   https://learn.microsoft.com/en-us/training/modules/configure-network-security-groups/4-determine-network-security-groups-effective-rules
   "VM 4: Subnet 3: none, NIC: none Azure default rules apply to both subnet and NIC and all inbound traffic is allowed"

4. The Azure Portal, when you create a VM with NIC network security group: None
   "All ports on this virtual machine may be exposed to the public internet. This is a security risk. Use a network security group to limit public access to specific ports. You can also select a subnet that already has network security groups defined or remove the public IP address."

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Document Details

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• ID: cd190c21-5b50-87ba-37dd-0b0c017ec6fb
• Version Independent ID: d9720147-207c-4c98-ba8d-016ff4b6ad60
• Content: Network security group - how it works
• Content Source: articles/virtual-network/network-security-group-how-it-works.md
• Service: virtual-network
• GitHub Login: @asudbring
• Microsoft Alias: allensu

[PesalaPavan]

@carlos-quintero
Thanks for your feedback! We will investigate and update as appropriate.

[ManoharLakkoju-MSFT]

@carlos-quintero
Thank you for bringing this to our attention.
I've delegated this to content author @asudbring, who will review it and offer their insightful opinions.