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Cisco Nexus 1000v VXLAN don't work

Hi to all,

I configured VXLAN configuration by the book (Cisco Nexus 1000V VXLAN Configuration Guide, Release 4.2(1)SV1(5.1)), but there is some problem.

There are two ESXs with four VMs (two VMs on each ESX). Each VM has one NIC and that NIC is assigned to a port-profile configured for same VXLAN bridge-domain access. There is connectivity between VMs on same ESX but there is no connectivity between VMs hosted on different ESXs. In other words, L2 connectivity works between VMs on same ESX but not between VMs on different ESXs.

Nexus 1000V VSM is installed on Nexus 1010 Appliance and manages two VEMs through L3 control interfaces.

VSM version is 4.2(1)SV1(5.1) and VEM feature level is 4.2(1)SV1(5.1).

Bridge-domain is VXLAN-5001 with segment id 5001 and group address

Port-profile for VMK VXLAN interface is properly configured for access to VLAN 588 ("transport" VLAN for VXLAN) and capability vxlan.

VLAN 588 is allowed on all uplinks on both sides (Nexus and physical switch).

Port profile for VMs if properly configured for access to bridge-domain.

I was create a monitor session for VLAN 588 on upstrean switch (Cisco 6513 with 12.2(18)SXF14 IOS) and  did't see any multicast, unicast or any other traffic. According to documentation, first I shuld to see IGMP join, after that multicast and after that unicast traffic between two VMK interfaces.

Here is MAC address table for bridge-domain VXLAN-5001:

Nexus1000V-VSM-1# sh mac address-table bridge-domain VXLAN-5001

Bridge-domain: VXLAN-5001
          MAC Address       Type    Age       Port            IP Address     Mod
          0050.56a3.0009    static  0         Veth6          3 
          0050.56a3.000a    static  0         Veth7          3 
          0050.56a3.0007    static  0         Veth4          4 
          0050.56a3.0008    static  0         Veth5          4 
Total MAC Addresses: 4

As you can see, there is no proper destination IP addresses.

Can somebody help me?

Cisco Employee

Cisco Nexus 1000v VXLAN don't work

Can you check the MTU size of the ports from the Cat going to the ESX hosts?

The MTU size needs to be set to 1550. We require a larger MTU to carry the additional VXLAN information.

Usually when VXLAN does not work between hosts MTU size is the culprit.

Also are you doing this with vCloud Director?


Community Member

Re: Cisco Nexus 1000v VXLAN don't work

Good hint, but it seems that is not the problem...

Cat ports connecting VEMs support jumbo frames and their MTU is set to 9216B.

I saw that MTU on Ethernet interfaces of VEMs is set to 1500B, I changed uplink port-profile and set MTU to first to 1550B, and after that to 9000B (max), but thing still isn't working.

I'm not using vCloud director, just VMware vSphere 4.1 (vCenter Server with VUM, vCenter Client and two ESX hosts).

Message was edited by: Mate Grbavac

After little research I found something strange... I setted up SVI on Cat in Vlan 588 ("transport" VLAN for VXLAN) and when I ping VMKernel interface (with capabilitiy vxlan) with packet size more than 1500B and df bit set I have no reply. My Cat ports and UpLink port profiles are configured for jumbo frames. Is it possible to change MTU of VMKernel interface?

Cisco Employee

Re: Cisco Nexus 1000v VXLAN don't work

If I recall correctly you don't need modify the VMK interface. The VEM will automatically do that for you if traffic being transported is VXLAN. As long as the uplink ports are all set for 1550 or greater it should be ok.

Since you are using a Cat 6513 igmp querier should be on by default but if you could check to be sure that would help.

Could post a running-config and output from

module vem execute vemcmd show vxlan interfaces

module vem execute vemcmd show vxlan-stats



Community Member

Re: Cisco Nexus 1000v VXLAN don't work

It works... Finnaly... :-)

Configuration guide for VXLAN is very bad, there is no infomation about need for IGMP querier or L3 multicast device if you have VXLAN VMkernels connected in L2 (VLAN 588 that I mentioned in first post).

After adding a router to VLAN 588 ("transport" VLAN for VXLAN) with IP Multicast enabled everything works fine.

I didn't started IGMP querier on Cat 6513 because it is high production component and it was much easier to me put RTR in VLAN 588.

Cisco Employee

Re: Cisco Nexus 1000v VXLAN don't work

Glad you got it working. I'll take a look at the guide and see if I can get the documentation team to clearly spell out the requirements.


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