%SW_MATM-4-MACFLAP_NOTIF: Host 286e.d422.926d in vlan 1 is flapping between port Gi1/0/12 and port Gi1/0/9

[Muhammad H. Usmani]

Hi all,

For a few days I have been observing vlan1 to be flapping between 2 ports of two 3750E switches (2 ports on each switch) which are cross connected to each other. Out of these 2 ports on each switch, one is that cross connectivity port. Stats are pasted below for both switches

1st Switch:

*Mar 14 00:06:27.336: %SW_MATM-4-MACFLAP_NOTIF: Host 286e.d422.926d in vlan 1 is flapping between port Gi1/0/26 and port Gi1/0/25
*Mar 14 00:10:58.900: %SW_MATM-4-MACFLAP_NOTIF: Host 286e.d422.926d in vlan 1 is flapping between port Gi1/0/25 and port Gi1/0/26
*Mar 14 00:17:57.635: %SW_MATM-4-MACFLAP_NOTIF: Host 286e.d422.926d in vlan 1 is flapping between port Gi1/0/25 and port Gi1/0/26
*Mar 14 01:28:06.971: %SW_MATM-4-MACFLAP_NOTIF: Host 286e.d422.926d in vlan 1 is flapping between port Gi1/0/26 and port Gi1/0/25
*Mar 14 01:48:04.805: %SW_MATM-4-MACFLAP_NOTIF: Host 286e.d422.926d in vlan 1 is flapping between port Gi1/0/25 and port Gi1/0/26
*Mar 14 01:48:46.664: %SW_MATM-4-MACFLAP_NOTIF: Host 286e.d422.926d in vlan 1 is flapping between port Gi1/0/25 and port Gi1/0/26
*Mar 14 01:49:49.218: %SW_MATM-4-MACFLAP_NOTIF: Host 286e.d422.926d in vlan 1 is flapping between port Gi1/0/25 and port Gi1/0/26
*Mar 14 01:56:06.001: %SW_MATM-4-MACFLAP_NOTIF: Host 286e.d422.926d in vlan 1 is flapping between port Gi1/0/25 and port Gi1/0/26
*Mar 14 02:58:11.927: %SW_MATM-4-MACFLAP_NOTIF: Host 286e.d422.926d in vlan 1 is flapping between port Gi1/0/25 and port Gi1/0/26
*Mar 14 03:02:07.529: %SW_MATM-4-MACFLAP_NOTIF: Host 286e.d422.926d in vlan 1 is flapping between port Gi1/0/25 and port Gi1/0/26
*Mar 14 03:03:13.674: %SW_MATM-4-MACFLAP_NOTIF: Host 286e.d422.926d in vlan 1 is flapping between port Gi1/0/25 and port Gi1/0/26

Out of this port Gi1/0/25 is connected with the second switch

2nd Switch:

Mar 14 04:29:55.309: %SW_MATM-4-MACFLAP_NOTIF: Host 286e.d422.926d in vlan 1 is flapping between port Gi1/0/12 and port Gi1/0/9
Mar 14 04:30:25.123: %SW_MATM-4-MACFLAP_NOTIF: Host 286e.d422.926d in vlan 1 is flapping between port Gi1/0/12 and port Gi1/0/9
Mar 14 04:31:44.965: %SW_MATM-4-MACFLAP_NOTIF: Host 286e.d422.926d in vlan 1 is flapping between port Gi1/0/12 and port Gi1/0/9
Mar 14 04:31:54.856: %SW_MATM-4-MACFLAP_NOTIF: Host 286e.d422.926d in vlan 1 is flapping between port Gi1/0/12 and port Gi1/0/9

out of these port Gi1/0/12 is used for cross connectivity.

I am using other switches two cross connected to each other and I have matched and verified the configuration but the issue still persists. Is there any other solution to this rather then Etherchannel configuration? As apart from the given two switches, I am not observing these errors on any other switch.

[Leo Laohoo]

That error message always means someone didn't configure etherchannel.

[Muhammad H. Usmani]

1st Switch:

Gi1/0/12 up up "CROSS CONNECTIVITY WITH NEW SWITCH"

interface GigabitEthernet1/0/12
description "CROSS CONNECTIVITY WITH NEW SWITCH"
switchport mode dynamic desirable
load-interval 30
no cdp enable

2nd Switch:

Gi1/0/25 up up "CROSS CONNECTIVITY WITH OLD SWITCH"

interface GigabitEthernet1/0/25
description "CROSS CONNECTIVITY WITH OLD SWITCH"
switchport mode dynamic desirable
load-interval 30
no cdp enable

Please find the config on both the switches. This same configuration is currently also running on other switches too that are cross connected exactly in the same environment and not showing the given error.

[Leo Laohoo]

---

@Muhammad H. Usmani wrote:

*Mar 14 01:56:06.001: %SW_MATM-4-MACFLAP_NOTIF: Host 286e.d422.926d in vlan 1 is flapping between port Gi1/0/25 and port Gi1/0/26

---

Can you post the complete output to the following commands: 

1.  sh mac add inter Gi 1/0/25; 

2.  sh mac add inter Gi 1/0/26

If Gi 1/0/26 is not a switch port, there should be, at most, two MAC addresses appearing.  If there's more, then someone's either NOT configured Etherchannel correctly or someone has installed a hub/switch under your nose.

[Muhammad H. Usmani]

@Leo Laohoo  Please find below the stats as requested

Switch#sh mac addr int gi1/0/26
Mac Address Table
-------------------------------------------

Vlan Mac Address Type Ports
---- ----------- -------- -----

Switch#sh mac addr int gi1/0/25
Mac Address Table
-------------------------------------------

Vlan Mac Address Type Ports
---- ----------- -------- -----
1 0005.0053.941b DYNAMIC Gi1/0/25
1 0011.5c96.991b DYNAMIC Gi1/0/25
1 0014.f265.ec38 DYNAMIC Gi1/0/25
1 0015.fa72.a9c0 DYNAMIC Gi1/0/25
1 0018.190d.36a9 DYNAMIC Gi1/0/25
1 001a.e23d.a22e DYNAMIC Gi1/0/25
1 001a.e23d.a22f DYNAMIC Gi1/0/25
1 001b.5445.a497 DYNAMIC Gi1/0/25
1 001b.5445.a498 DYNAMIC Gi1/0/25
1 001b.7899.8f82 DYNAMIC Gi1/0/25
1 001c.f965.d785 DYNAMIC Gi1/0/25
1 001f.29e5.1d36 DYNAMIC Gi1/0/25
1 0021.567e.7540 DYNAMIC Gi1/0/25
1 0021.5ad7.c4d0 DYNAMIC Gi1/0/25
1 0024.516c.1c8d DYNAMIC Gi1/0/25
1 0024.c31a.16af DYNAMIC Gi1/0/25
1 0024.c31a.16b0 DYNAMIC Gi1/0/25
1 0024.c31a.4b40 DYNAMIC Gi1/0/25
1 0025.b436.372b DYNAMIC Gi1/0/25
1 0025.b436.372c DYNAMIC Gi1/0/25
1 0026.5532.ad82 DYNAMIC Gi1/0/25
1 580a.20d0.338c DYNAMIC Gi1/0/25
1 580a.20d0.33c0 DYNAMIC Gi1/0/25
1 68ef.bd90.b281 DYNAMIC Gi1/0/25
1 bc67.1c95.d514 DYNAMIC Gi1/0/25
1 d4d7.488c.bc17 DYNAMIC Gi1/0/25
1 d4d7.488c.bc18 DYNAMIC Gi1/0/25
1 d8b1.22e7.740b DYNAMIC Gi1/0/25
1 d8b1.22e7.740c DYNAMIC Gi1/0/25
1 d8b1.22e7.740d DYNAMIC Gi1/0/25
Total Mac Addresses for this criterion: 30

[Leo Laohoo]

30 unique MAC address connected to an access port. What does that tell you?
To me, it tells me that someone has connected, at least, a 48-port switch without your knowledge. I suspect the same output from port Gi 1/0/26.
So what happens if you enable BPDU Guard on that port?

[Muhammad H. Usmani]

@Leo Laohoo   I mentioned earlier too that I am observing this error on 2 switches, both switches are showing the same behaviour on the ports where I have laid the cables for cross connecting both of these switches. Find the descriptions and mac address tables below for both switches specifically on the ports involved in cross connectivity.

Switch 1:

Gi1/0/12 up up "CROSS CONNECTIVITY WITH NEW SWITCH"

Switch-1#show mac address-table interface Gi1/0/12
Mac Address Table
-------------------------------------------

Vlan Mac Address Type Ports
---- ----------- -------- -----
1 0026.0b5f.3599 DYNAMIC Gi1/0/12
2 0026.0b5f.3599 DYNAMIC Gi1/0/12
3 0026.0b5f.3599 DYNAMIC Gi1/0/12
4 0026.0b5f.3599 DYNAMIC Gi1/0/12
5 0026.0b5f.3599 DYNAMIC Gi1/0/12
6 0026.0b5f.3599 DYNAMIC Gi1/0/12
8 0026.0b5f.3599 DYNAMIC Gi1/0/12
9 0026.0b5f.3599 DYNAMIC Gi1/0/12
11 0026.0b5f.3599 DYNAMIC Gi1/0/12
12 0026.0b5f.3599 DYNAMIC Gi1/0/12
13 0026.0b5f.3599 DYNAMIC Gi1/0/12
14 0026.0b5f.3599 DYNAMIC Gi1/0/12
16 0026.0b5f.3599 DYNAMIC Gi1/0/12
17 0026.0b5f.3599 DYNAMIC Gi1/0/12
18 0026.0b5f.3599 DYNAMIC Gi1/0/12
19 0026.0b5f.3599 DYNAMIC Gi1/0/12
20 0026.0b5f.3599 DYNAMIC Gi1/0/12
21 0026.0b5f.3599 DYNAMIC Gi1/0/12
22 0026.0b5f.3599 DYNAMIC Gi1/0/12
23 0026.0b5f.3599 DYNAMIC Gi1/0/12
25 0026.0b5f.3599 DYNAMIC Gi1/0/12
26 0026.0b5f.3599 DYNAMIC Gi1/0/12
27 0026.0b5f.3599 DYNAMIC Gi1/0/12
28 0026.0b5f.3599 DYNAMIC Gi1/0/12
29 0026.0b5f.3599 DYNAMIC Gi1/0/12
30 0026.0b5f.3599 DYNAMIC Gi1/0/12
31 0026.0b5f.3599 DYNAMIC Gi1/0/12
32 0026.0b5f.3599 DYNAMIC Gi1/0/12
33 0026.0b5f.3599 DYNAMIC Gi1/0/12
34 0026.0b5f.3599 DYNAMIC Gi1/0/12
35 0026.0b5f.3599 DYNAMIC Gi1/0/12
36 0026.0b5f.3599 DYNAMIC Gi1/0/12
37 0026.0b5f.3599 DYNAMIC Gi1/0/12
38 0026.0b5f.3599 DYNAMIC Gi1/0/12
999 0026.0b5f.3599 DYNAMIC Gi1/0/12
10 0026.0b5f.3599 DYNAMIC Gi1/0/12
100 0026.0b5f.3599 DYNAMIC Gi1/0/12
101 0026.0b5f.3599 DYNAMIC Gi1/0/12
102 0026.0b5f.3599 DYNAMIC Gi1/0/12
1001 0026.0b5f.3599 DYNAMIC Gi1/0/12
Total Mac Addresses for this criterion: 40

Switch 2:

Gi1/0/25 up up "CROSS CONNECTIVITY WITH OLD SWITCH"

Switch-2#sh mac addr int Gi1/0/25
Mac Address Table
-------------------------------------------

Vlan Mac Address Type Ports
---- ----------- -------- -----
1 0011.5c96.991b DYNAMIC Gi1/0/25
1 0014.f265.ec38 DYNAMIC Gi1/0/25
1 0015.fa72.a9c0 DYNAMIC Gi1/0/25
1 0018.190d.36a9 DYNAMIC Gi1/0/25
1 001b.7899.8f82 DYNAMIC Gi1/0/25
1 001f.29e5.1d36 DYNAMIC Gi1/0/25
1 0021.567e.7540 DYNAMIC Gi1/0/25
1 0021.5ad7.c4d0 DYNAMIC Gi1/0/25
1 0024.516c.1c8d DYNAMIC Gi1/0/25
1 0024.c31a.4b40 DYNAMIC Gi1/0/25
1 580a.20d0.338c DYNAMIC Gi1/0/25
1 580a.20d0.33c0 DYNAMIC Gi1/0/25
1 68ef.bd90.b281 DYNAMIC Gi1/0/25
1 bc67.1c95.d514 DYNAMIC Gi1/0/25
1 d8b1.22e7.740b DYNAMIC Gi1/0/25
1 d8b1.22e7.740c DYNAMIC Gi1/0/25
1 d8b1.22e7.740d DYNAMIC Gi1/0/25
Total Mac Addresses for this criterion: 17

So that 48-port switch is not connected without my knowledge but I have connected it myself. Though I didn't implement BPDU guard on any of them.

[mario.jost]

So as far as i understand this post, you have connected two switches with 1 cable. But based on the error messages, it seems that these switches have an additional connection between them.

 SwitchA Gi1/0/12 - - - - - - - - - - Gi1/0/25 SwitchB
 SwtichA Gi1/0/9  - - - - - - - - - - Gi1/0/26 SwitchB

They dont have to be directly connected. It could be that there is another switch in between SwitchA Gi1/0/9 and SwitchB Gi1/0/26. So if you have 2 connections between a switch either you have to use a bundling technology like etherchannel or you one port should block traffic with spanning-tree. Can you do a show spanning-tree vlan1 to check if one of these ports are beeing blocked due to redundancy.

[Muhammad H. Usmani]

@mario.jost  Basically I have connected 3 switches (3rd switch was not a part of discussion but as you mentioned the connectivity so they are connected as follows)

Switch A Gi1/0/25 --------> Switch B Gi1/0/12

Switch A Gi1/0/26 & Switch B Gi1/0/9 ---------> Switch C (Switch of Service Provider)

I kept the service provider's switch out of discussion because as per my understanding, it has nothing to do with this situation. So I am just using one connection for one switch (i.e Switch A and Switch B are connected via only one port). As far as spanning-tree is concerned. Please find it as follows:

Switch A:

VLAN0001
Spanning tree enabled protocol rstp
Root ID Priority 0
Address 000a.b8c3.5700
Cost 23
Port 25 (GigabitEthernet1/0/25)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 0026.0b5f.3580
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/0/25 Root FWD 4 128.25 P2p
Gi1/0/26 Desg FWD 19 128.26 P2p
Gi1/0/27 Desg FWD 4 128.27 P2p
Gi1/0/29 Desg FWD 4 128.29 P2p

Switch B:

VLAN0001
Spanning tree enabled protocol rstp
Root ID Priority 0
Address 000a.b8c3.5700
Cost 19
Port 21 (GigabitEthernet1/0/21)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 580a.20d0.3380
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/0/1 Desg FWD 19 128.1 P2p
Gi1/0/2 Desg FWD 4 128.2 P2p
Gi1/0/5 Desg FWD 19 128.5 P2p
Gi1/0/9 Desg FWD 4 128.9 P2p
Gi1/0/12 Desg FWD 4 128.12 P2p
Gi1/0/13 Desg FWD 4 128.13 P2p
Gi1/0/15 Desg FWD 19 128.15 P2p
Gi1/0/16 Desg FWD 19 128.16 P2p
Gi1/0/19 Desg FWD 4 128.19 P2p
Gi1/0/21 Root FWD 19 128.21 P2p
Gi1/0/22 Desg FWD 4 128.22 P2p
Gi1/0/24 Desg FWD 4 128.24 P2p

[Leo Laohoo · Accepted solution]

You will need to trace those MAC address visually. Somewhere between your core switch and those MAC address is an un-managed switch that has two (or more) uplinks going to your switch thereby forming a loop.

[Dennis Mink · Accepted solution]

Move away from usinhvlan1