A VM with Multiple IP Addresses configured on a Single vNIC experiencing communication issues with all IP's except one

Products

• VMware NSX

Issue/Introduction

• Multiple IP addresses are configured on the network adapter within the guest OS or application.
• Examining the Inventory tab in NSX reveals that only one of the IP addresses is being listed.
• The additional IP addresses are not recognized by NSX and may appear unreachable when tested from other systems.

Environment

VMware NSX 4.x

Cause

• This behavior occurs because the default NSX IP Discovery Profile enforces an ARP binding limit of one.
• This setting allows NSX to track and store only the first IP address discovered per MAC address (vNIC).
• When multiple IPs are configured on the same interface, NSX records only the first binding. As a result, the remaining IPs are not learned, leading to incomplete IP visibility and reachability issues within the NSX environment.
• When a group uses “Connected to Segment” as its membership criterion, NSX identifies connected VMs based on discovered IP-to-MAC bindings.  As a result, when relying on the default IP Discovery Profile, having multiple IP addresses configured on the same vNIC will result in only the lowest IP being learned and added to the group. Depending on where this Group is being used (DFW rules, network introspection rules, etc....), this could cause major communication disruptions. 

Resolution

To ensure that all virtual IPs associated with the VM are recognized correctly, follow one of the below approaches:

• Option 1 : Create a Custom IP Discovery Profile:
  • Navigate to Networking > Segments > Profiles > IP Discovery Profiles.
  • Create a new IP Discovery Profile.
  • Increase the ARP Binding Limit value to accommodate all the IPs configured on the VM interface.
  • Apply this new IP Discovery Profile to the corresponding Segment.
    
    
• Option 2 : Manually Adjust Group Membership: (If being used)
  • Edit the affected Group.
  • Remove the incorrect IP that was automatically included.
  • Manually add the correct IP addresses or VM objects as required.

Additional Information

Create an NSX IP Discovery Segment Profile