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Host in vlan flapping between two interfaces

Posted on 2010-11-27
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Last Modified: 2012-05-10
Hi There,

I'm having an issue with two interfaces flapping in vlan 30.
The two switchports are connected to two different servers. Both servers have dual nics and are connecting to switch1 and switch 2 respectively

The  WS-C3750- shows two mac entries for   Fa1/0/17 for some reason.

Any advise would be greatful. see the logs below



SW01 log
######################################################
etween port Gi0/46 and port Gi0/41
14:10:53: %SW_MATM-4-MACFLAP_NOTIF: Host 0201.0000.0000 in vlan 30 is flappin
etween port Gi0/44 and port Gi0/46
14:11:08: %SW_MATM-4-MACFLAP_NOTIF: Host 0201.0000.0000 in vlan 30 is flappin
etween port Gi0/46 and port Gi0/41
14:11:23: %SW_MATM-4-MACFLAP_NOTIF: Host 0201.0000.0000 in vlan 30 is flappin
etween port Gi0/44 and port Gi0/46
######################################################


SW01 CDP Neighbor on SW01
######################################################
SW01#sh cdp ne
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone

Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID
SW01#Gig 0/11          145           S I      WS-C2950T Fas 0/4
SW01#Gig 0/46          170          R S I    WS-C3750- Fas 1/0/24


SW01#show mac-address-table interface gi0/44
########################################################

          Mac Address Table
-------------------------------------------

Vlan    Mac Address       Type        Ports
----    -----------       --------    -----
  30    0022.1954.7a72    DYNAMIC     Gi0/44
Total Mac Addresses for this criterion: 1



show log on SW2 WS-C3750
######################################################

00:56:42: %SW_MATM-4-MACFLAP_NOTIF: Host 0201.0000.0000 in vlan 30 is flapping
etween port Fa1/0/17 and port Fa1/0/24
01:09:32: %SW_MATM-4-MACFLAP_NOTIF: Host 0201.0000.0000 in vlan 30 is flapping
etween port Fa1/0/17 and port Fa1/0/24

######################################################

SW02#sh cdp ne

MNACEDPKSW01     Fas 1/0/24        125           S I      WS-C2960G Gig 0/46
SW02#


Two mac addresses learned on   WS-C3750

SW02#show mac-address-table interface fa1/0/17
######################################################

          Mac Address Table
-------------------------------------------

Vlan    Mac Address       Type        Ports
----    -----------       --------    -----
  30    0022.1954.7a70    DYNAMIC     Fa1/0/17
  30    0201.0000.0000    DYNAMIC     Fa1/0/17
Total Mac Addresses for this criterion: 2































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Question by:MCP200
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5 Comments
 
LVL 8

Accepted Solution

by:
ludo_friend earned 250 total points
ID: 34224842

0201.0000.0000 is not real mac (well not a real physical mac), it's used by network load balancing.  if you're running this on two different servers, it will assign the same mac, and thats why you're flapping between ports.

easiest way to fix this is to get the windows network load balancer disabled, and use an etherchannel compatible aggregation method to achieve switch redundancy. your 3750's allow stacking via a stackwise cable loop, I highly recommend doing it this way instead. Depending on your goal here, you may not be able to do this.

if you can't,  you'll have to follow this guide from cisco.
http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_example09186a0080a07203.shtml
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Author Comment

by:MCP200
ID: 34224870
Thanks for the reply,

Would you say this is the reason it's causing my Remote Desktop to drop out ?

Many Thanks
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LVL 8

Assisted Solution

by:ludo_friend
ludo_friend earned 250 total points
ID: 34227035
most likely. the mac entry in the address table will be changing between ports, this means at some point, the packets will never make it to the server in which they are destined.


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LVL 8

Expert Comment

by:SeeMeShakinMyHead
ID: 34228909
Agree 100% with ludo.  
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Author Comment

by:MCP200
ID: 34229023
I disabled load balancing and i no longer see the flaps in the show log but my rdp still drops out.
I will configure etherchannel for the server and i see how i go,

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