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SW_MATM-4-MACFLAP_NOTIF

frede_frede
Level 1
Level 1

Hi

I have a big problem with Vlan flapping, this is my topology

Desenho1.gif

Switch 1 and Switch 2 have the SVI and HSRP configured. Switch 1 is the root bridge for all Vlans. The message vlan X is flapping between port Gi1/0/2 and port Po2 appears on Switch 3. The Po2 is connected to Switch 1.

The port settings in Sw3:

spanning-tree mode pvst

spanning-tree extend system-id

spanning-tree vlan 1-4094 priority 12288

interface Port-channel1

description "Sw2"

switchport trunk encapsulation dot1q

switchport trunk allowed vlan 10,11,12,13

switchport mode trunk

switchport nonegotiate

spanning-tree vlan 1-4094 cost 6

!

interface Port-channel2

description "Sw1"

switchport trunk encapsulation dot1q

switchport trunk allowed vlan 10,11,12,13

switchport mode trunk

switchport nonegotiate

interface GigabitEthernet1/0/21

description "Sw2"

switchport trunk encapsulation dot1q

switchport trunk allowed vlan 10,11,12,13

switchport mode trunk

switchport nonegotiate

channel-group 1 mode passive

!

interface GigabitEthernet1/0/22

description "Sw2"

switchport trunk encapsulation dot1q

switchport trunk allowed vlan 10,11,12,13

switchport mode trunk

switchport nonegotiate

channel-group 1 mode passive

!

interface GigabitEthernet1/0/23

description "Sw1"

switchport trunk encapsulation dot1q

switchport trunk allowed vlan 10,11,12,13

switchport mode trunk

switchport nonegotiate

channel-group 2 mode passive

!

interface GigabitEthernet1/0/24

description "Sw1"

switchport trunk encapsulation dot1q

switchport trunk allowed vlan 10,11,12,13

switchport mode trunk

switchport nonegotiate

channel-group 2 mode passive

In switch 1 and 2 settings are the same except the mode of the channel-group which is active.

I think the problem with "vlan X is flapping" is on the doors of servers that have more than one nic connected to the switch, a misconfiguration can cause the message "Vlan X is flapping Between port Gi1/0/2and port Po2 " and others messages, I say this because this message only appears in configured ports of two VLANs and not in the other two.

Is there any way to prevent such events, even if the problem is the servers?

Thank you for your help

1 Accepted Solution

Accepted Solutions

Hi Fred,

I would suggest you to check for the TCNs for those VLANs (command : show spanning-tree vlan 10 detail). To may want to see the incrementing numbers of TCNs. It even mentions the last topology change notification from which interface.

You may need to monitor the above for a day or so to figure out if it's related to STP.

This issue can be due to multiple factors like UDLD, Server-side LB mechanism etc. Hit each of the points.

Regards

Vivek

View solution in original post

20 Replies 20

Peter Paluch
Cisco Employee
Cisco Employee

Hello Frederico,

Your observation is most probably correct. I do not see any obvious problem in your EtherChannel configuration, and I praise very much the fact that you are using LACP to negotiate the creation of your EtherChannels. If the servers are using multiple NICs, it may be necessary to use teaming or other special functionality to make the operating system on these servers to use the NICs properly. I have seen Windows, for example, sending an ARP reply containing MAC address of one NIC through the other NIC, causing some hard-to-debug flooding issues in a switched network. There may be other issues as well.

Sadly, there is nothing to immediately do to prevent these issues from occuring. Where exactly are the servers connected in your topology - which switches and which ports?

Best regards,

Peter

HI Peter

The System Administrator has configured teaming. I have 8 servers connected to the switch 3, all with two doors, except one with 4. Only two servers, vlan servers 10 and 11 show problems. The configuration on access doors is the same, except the vlan. The flapping does not appear every day, when there lasts only one minute (minute that it creates instability in the entire network) and then return everything to normal.

It is not strange that the MAC address appears on the access port and in the Po that makes the trunk to the switch1?

Thanks

Fred

Another strange thing. In switches 1 and 2, they are two 6500 with FWSM, while I'm receiving the flapping msg  I get the following msg in the 6500 "% SVCLC-5-FWTRUNK: Firewalled VLANs configured on trunks," but the Vlans allowed on the trunks of SW1 SW2 and SW3 are all the same.

Thanks

Fred

Hello Fred,

Can you update the picture to include the position of one server that exhibits the MAC flapping problem? In the meanwhile, I will try to look up the meaning of the SVCLC message.

Best regards,

Peter

Hi Fred,

Just to add backing to yours & Peters theories, I've seen the exact message several times on 3750-X series switches and it's normally one of the following:

A) The Servers Networks cards are configured for EtherChannel or LACP (Depending on teaming software) and the switch side of the connection isn't.

B) The Servers aren't fully teamed but are using some form of Transmit Load Balancing (sometimes a default NIC setting with some vendors).

As Peter said though, if you could provide a diagram with the servers in question and how the fit in the topology physically (in terms of connections to which switch)...

HTH

First of all thank you for your help.

Here is the update of the topology:

Best regards

Fred

Hi Duncan,

when you saw these messages, the flapping was between an access port and a trunk port?

Thanks for the help

Fred