VM showing up on two switches

Patrick McHenry · ‎03-08-2011

We have a VM that is experiencing some connectivity problems.

One mac is showing up on two different ports on two different VLANs. I know that Gi0/25 is a trunk port so it makes sense that it is showing up on that port but, why is it showing up on VLAN 1 when the VM is on 17? Also, why is it showing up on two switches. Should I clear the mac address table of that address on both switches? then see if it comes back to only one?

Vlan    Mac Address       Type        Ports
----    -----------       --------    -----
   1    000c.2991.165d    DYNAMIC     Gi0/25
17    000c.2991.165d    DYNAMIC     Gi0/6

Vlan    Mac Address       Type        Ports
----    -----------       --------    -----
   1    000c.2991.165d    DYNAMIC     Gi0/17
17    000c.2991.165d    DYNAMIC     Gi0/25

Thanks, Pat.

DuncanM2008 · ‎03-08-2011

Hi Patrick,

Is this by any chance a VM running on VMWare ESX?

If so VMWare vSwitches use a form of transmit load-balancing by default although it sounds more like your ESX side of things is configured for a link aggregation method "Route based on IP Hash" but your switches aren't.

Could you possibly give us some more information on the VM platform and configured networking, i.e. is the VM attached to a vswitch with multiple physical network cards? what hypervisor are you running?

Thanks,

Patrick McHenry · ‎03-11-2011

Hi Duncan,

Thank you for the response. Yes, it is indeed running on ESX... specifically, vSphere 4.0.

Currently, the host that this VM is running on is connected via two sets of two gigabit NICs to two different switches (two NICs to each switch, for redundancy). On the switches, they are configured as trunk ports... on the VMware host, all four ports are part of the same virtual switch (with a separate virtual machine port group for each vlan that VMs connect to). This virtual switch is set up to route based on the originating virtual port ID, with network failover detection set for link status only. The VM has a sole NIC attached to one virtual machine port group (for our VLAN 17). All management/VMotion/FT connections are assigned to different (unique) physical NICs, and none of those connections use a trunk port or a NIC on vlan 1 (our network vlan). Does that information help?

DuncanM2008 · ‎03-14-2011

Hi Patrick,

The ESX side of things sounds fine in that your not attempting any load-balancing/link-aggregation so shouldn't be seeing the MAC on two different switches.

Slightly more interesting is the fact the same MAC is showing up on both switches in 2 different VLAN's, what are these switches doing in terms of Layer 3 functionality?

Could you possibly post a bit of the relevant configuration + sanitize the sensitive information please?

Thanks,

Patrick McHenry · ‎03-16-2011

Duncan,

we aren't using any layer 3 in the access layer - just trunk ports to the core. I did notice that the trunk port is using portfast but, that shouldn't matter should it? I probably shouldn't be using portfast on a trunk port though. Here is some interface ans spanning tree output. Is there any specific output you would like to see?

Thanks, Pat.

NCR02#sh run int g0/18
Building configuration...

Current configuration : 171 bytes
!
description ESX

switchport access vlan 2

switchport trunk encapsulation dot1q

switchport mode trunk

spanning-tree portfast

end

VLAN0002
Spanning tree enabled protocol rstp
Root ID    Priority    8192
             Address     0015.2c03.1002
             Cost        4
             Port        25 (GigabitEthernet0/25)
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority    32770 (priority 32768 sys-id-ext 2)
             Address     0015.621c.bf80
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Gi0/2            Desg FWD 19        128.2    Edge P2p
Gi0/5            Desg FWD 19        128.5    Edge P2p
Gi0/9            Desg FWD 4         128.9    Edge P2p
Gi0/11           Desg FWD 4         128.11   Edge P2p
Gi0/12           Desg FWD 4         128.12   Edge P2p
Gi0/18           Desg FWD 4         128.18   P2p
Gi0/23           Desg FWD 4         128.23   P2p
Gi0/25           Root FWD 4         128.25   P2p

NCR02#sh int g0/18 sw
Name: Gi0/18
Switchport: Enabled
Administrative Mode: trunk
Operational Mode: trunk
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: On
Access Mode VLAN: 2 (Users1)
Trunking Native Mode VLAN: 1 (default)
Administrative Native VLAN tagging: enabled
Voice VLAN: none
Administrative private-vlan host-association: none
Administrative private-vlan mapping: none
Administrative private-vlan trunk native VLAN: none
Administrative private-vlan trunk Native VLAN tagging: enabled
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk private VLANs: none
Operational private-vlan: none
Trunking VLANs Enabled: ALL
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Capture VLANs Allowed: ALL

Protected: false
Unknown unicast blocked: disabled
Unknown multicast blocked: disabled
Appliance trust: none