Virtual Machine Network Connectivity Issues Over L2VPN via NSX Autonomous Edge

Products

VMware NSX

Issue/Introduction

Virtual machines (VMs) experience network connectivity loss, degraded performance, or packet drops when communicating over an L2VPN tunnel that terminates on an NSX Autonomous Edge.

Diagnostic Steps

Log in to the NSX Autonomous Edge CLI and check the MTU configuration for the uplink interface:

nsx_autonomous_edge_cli> get logical-routers
nsx_autonomous_edge_cli> vrf <vrf-number>
nsx_autonomous_edge_cli> get interfaces <interface-uuid>

Example Output:

Interface     : b6fe1a27-####-####-####-5be228854eb4
Ifuid         : 266
Name          : lrport_0
Fwd-mode      : IPV4_ONLY
Internal name : uplink-266
Mode          : lif
Port-type     : uplink
IP/Mask       : 192.168.###.###/24
MAC           : 00:50:56:##:##:##
VLAN          : 20
Access-VLAN   : untagged
LS port       : 057131be-####-####-####-84875802aab0
Urpf-mode     : STRICT_MODE
Admin         : up
Op_state      : up
MTU           : 1500  <-- Lower MTU observed

Log in to the NSX Managed Edge CLI at the opposite end of the L2VPN tunnel and check statistics for fragmentation or MTU mismatches:

nsx_edge_cli> get logical-router interface stats | more

Example Output:

interface   : 40892b08-####-####-####-91f36adc6094
ifuid       : 273
VRF         : 1b65cc35-####-####-####-d9cbe333509c
name        : test
IP/Mask     : 192.168.###.###/24
MTU         : 9000  <-- Higher MTU observed
statistics
    IP Ressemble
        Fragments-OK: #####
        Fragments-Error: #####
    IP Fragment
        Fragments-OK: #####
        Fragments-Error: #####

Environment

VMware NSX
VMware NSX Autonomous Edge
L2VPN Configuration

Cause

This issue occurs due to an MTU mismatch between the endpoints of the L2VPN tunnel (e.g., Autonomous Edge port set to 1500 while the peer Managed Edge port is set to 9000).

When large or jumbo frames pass through an L2VPN tunnel with mismatched MTU settings, packets are fragmented or dropped at the receiving boundary, causing severe packet loss, high latency, or complete connection failure.

Resolution

To resolve the MTU mismatch on the NSX Autonomous Edge, update the logical router port MTU to match the rest of the network fabric (e.g., 9000) using the Autonomous Edge REST API.

Note: Ideally, port MTU settings should be aligned during the initial installation by selecting the appropriate port group MTU.

Step-by-Step API Procedure

1.Identify the Logical Router Port UUID:

Execute a GET request to retrieve all logical ports on the Autonomous Edge:

GET https:///api/v1/ports

Locate the target logical router port (e.g., lrport_0) in the response and copy its id (UUID).

2.Retrieve Current Port Configuration:

Execute a GET request using the specific port UUID to fetch its current JSON payload:

GET https:///api/v1/ports/

Sample Output:

{
  "display_name": "lrport_0",
  "exit_interface": "eth2",
  "id": "",
  "mac_address": "##:##:##:##:##:##",
  "mtu": 1500,
  "resource_type": "LogicalRouterPort",
  "subnets": [
    {
      "ip_addresses": [
        ""
      ],
      "prefix_length": 24
    }
  ],
  "urpf_mode": "STRICT",
  "vlan_id": 
}

3.Modify the Payload MTU Value:

Copy the JSON body from Step 2. Update the "mtu" value from 1500 to 9000 (or your target network MTU size). Ensure all other fields remain unchanged.

4.Apply the Updated Configuration:

Send a PUT request containing the updated JSON body back to the target port endpoint:

PUT https:///api/v1/ports/

5.Verify the Update:

Re-run the GET request from Step 2 to confirm that "mtu": 9000 is now actively applied to the port:

{
  "display_name": "lrport_0",
  "exit_interface": "eth2",
  "id": "",
  "mac_address": "##:##:##:##:##:##",
  "mtu": 9000,
  "resource_type": "LogicalRouterPort",
  "subnets": [
    {
      "ip_addresses": [
        ""
      ],
      "prefix_length": 24
    }
  ],
  "urpf_mode": "STRICT",
  "vlan_id": 
}

Additional Information

Verify configuration of the L2VPN tunnel between sites

Troubleshooting NSX L2 VPN

Troubleshooting MTU issues and fragmentation in NSX fabric