Hi guys,
I have an issue with a Cisco 3750 switch stack which is connected to two seperate upstream Cisco 3750's which are administered by an ISP. The ISP is experiencing MAC address flapping from one of my VLAN SVI's i am using to route traffic upstream. Please see attached a diagram of the topology (put together very quickly).
%SW_MATM-4-MACFLAP_NOTIF: Host 1caa.0765.eac0 in vlan 3017 is flapping between port Gi1/0/48 and port Te1/0/2
%SW_MATM-4-MACFLAP_NOTIF: Host 1caa.0765.eac0 in vlan 3017 is flapping between port Te1/0/2 and port Gi1/0/48
%SW_MATM-4-MACFLAP_NOTIF: Host 1caa.0765.eac0 in vlan 3017 is flapping between port Gi1/0/48 and port Te1/0/2
%SW_MATM-4-MACFLAP_NOTIF: Host 1caa.0765.eac0 in vlan 3017 is flapping between port Gi1/0/48 and port Te1/0/2
%SW_MATM-4-MACFLAP_NOTIF: Host 1caa.0765.eac0 in vlan 3017 is flapping between port Te1/0/2 and port Gi1/0/48
Port Te1/0/2 is a ten gigabit trunk port connecting their two switches and ports Gi1/0/48 on both switches connect directly back to my switch stack.
I basically have been provided two connections from the ISP switches (ports Gi1/0/48 on both their switches) which are active/passive which i use to route traffic upstream. My switches are configured as follows -
interface Port-channel1
switchport mode access
spanning-tree bpdufilter enable
spanning-tree bpduguard enable
interface FastEthernet1/0/24 (Connected to Gi1/0/48 ISP switch #1)
description *************
switchport mode access
mls qos vlan-based
channel-group 1 mode on
spanning-tree portfast
spanning-tree bpdufilter enable
spanning-tree bpduguard enable
interface FastEthernet2/0/24 (Connected to Gi1/0/48 ISP switch #2)
description ****************
switchport mode access
mls qos vlan-based
channel-group 1 mode on
spanning-tree portfast
spanning-tree bpdufilter enable
spanning-tree bpduguard enable
interface Vlan1
ip address 1.1.1.1 255.255.255.248
no ip redirects
service-policy input ****************
ip route 0.0.0.0 0.0.0.0 1.1.1.2
As you can see I utilise a VLAN SVI to route traffic to the upstream 1.1.1.2 (illustration only) IP. As per the diagram of the topology attached, the ISP is receiving a MAC address flapping error confirming the SVI MAC address from my switch stack is being learnt on the trunk port connecting switch 1 and switch 2, and also the port (Gi1/0/48) directly connected to my switch stack. As these are all Layer 2 links essentially being passed upstream and then connected between the two ISP switches, we have a 3 way triangular loop formed.
What would be the best option to prevent this?
If I was to remove the port channel configuration from the two ports associated with the VLAN SVI, am i right in suggesting this would still form a layer 2 loop? The two ports would still be a member of the SVI VLAN, and it is the VLAN MAC address which is being learnt by the two ISP switches on different interfaces.
