VLAN flapping

[abdulkarim041]

Hi 

I am facing the following massages at my device.

May 10 02:00:39.793: %SW_MATM-4-MACFLAP_NOTIF: Host 0090.e846.98ee in vlan 105 is flapping between port Gi0/23 and port Gi0/4

As per my understanding there is some issue in VLAN 105 not at physical interface g0/23 and g0/4. I just want to know am i right?

BR

Abdul Karim

[paul driver]

Hello

This is a loop between those two interfaces -Basically the switch is complaining it seeing the same mac address on both those interfaces

What kind of ports are these? Do they have stp portfast enabled or stp disabled for that vlan or some bpdu filtering on them.

res

Paul

[abdulkarim041]

Tanks Paul

Below are the configurations of the ports as 

interface GigabitEthernet0/4
switchport trunk allowed vlan 105,113,213
switchport trunk encapsulation dot1q
switchport mode trunk
spanning-tree link-type shared
spanning-tree guard root
!

!
interface GigabitEthernet0/23
location civic-location-id none
switchport trunk allowed vlan 105,113,213
switchport trunk encapsulation dot1q
switchport mode trunk
!

Port g0/23 is connected with CISCO Core switch and port g0/4 is connected to MOXA switches through Red Lines communications wireless networks.

We have almost 10 MOXA switches at G0/4 

BR

AbdulKarim

[Furose M]

Hey Karim,

are you seeing this only on 1 vlan? and only for 1 MAC address? how frequent these messages are?

This MAC address seems to belonging to Moxa tech. are they participating in Spanning tree properly?

[paul driver]

Hello

Why do you bdpufilter enabled globally what is the requirement for this -this basically it ignores receipt of bpdu and and thus can allow forwarding of traffic on a link when it should be blocking.

I can see one interface ( I guess on the same switch) has root guard enable but the other inrface is allow to become a root.

if you know your network I would trace the trunks interfaces status and somewhere you should find an interface that should not be forwardiing but is.

Res

paul

[Carlos Villagran]

Hi!

This is clearly an issue with the path that frame is taking through the network. First I would take spanning-tree link-type shared configuration from the link to MOXAS since RSTP will not work as expected since you are stating this link is connected to a Half Duplex link.

Also, is your CORE switch the root bridge in the topology?.

Hope it helps, best regards!

JC

[abdulkarim041]

Thanks Paul for your reply

VLAN 105 is management the VLAN. Yes mentioned MAC address is MOXA switch MAC address. We have observed flapping in all others VLANs also.   

Spanning tree configurations on CISCO switch are as under:

spanning-tree portfast edge default
spanning-tree portfast edge bpdufilter default
spanning-tree extend system-id
spanning-tree mst 0 priority 24576

At MOXA switches we have configured RSTP.

BR

Abdul KArim

[Furose M]

RSTP is different than Cisco's RPVST. The only standard version of STP Cisco switches run is MST. if MOXA is not running Cisco compatible RSTP (i.e: RPVST), then change the spanning-tree mode everywhere to MST and it should take care of STP issues.

BPDU filter should be fine as it only gets enabled in Access port and we dont have any. so, it doesnt do anything.

[paul driver]

Hello

i do not think it is wise to have this feature  enabled globally if you DONT have any use for it and also it does provide a possible loop scenario if you do have access ports

if it not needed then don't enable it - this feature is basically for ports that you definitely know do not parciptiate it sending or receiving bpdu 

In the past I have actually used this feature  to stop stp blocking my ports in a lan migration

As for this issue it does seem to suggest an interface bit it a trunk or access port is forwarding when it shouldn't be

res

paul

[Furose M]

well Paul,

i must agree with you. bpdufilter = disabling STP.