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Bronze

Is a flapping mac address on a switch always a serious problem?

I've read several threads here about flapping mac addresses and I understand the causes, but I have two situations where it is occurring but I dont know if its really a problem.

First I have a 4006 in the center of about 20 2950 and 3548 switches. The 4006 reports macs flapping between its ports. The macs inquestion though are all wireless devices moving around in a warehouse where the access points are attached to the 2950s and 3548s. This seems like a normal situation. What are the issues that could make this bad?

Second, I have a 6509 with a host that thinks it is runnning an etherchannel only the switch doesnt see it that way. The 6509 is not complaining, I can only tell its flapping by showing the cam table repeatedly. The host is connected on two different modules on the 6509 so I need to manually form the channel group and turn channeling on for each port. Problem is this is a high availability host and forming the channel group will take it down for a short while. I can't get permission to do it yet. Is ther a way to get these flaps to log to see how often they are happening? Can anyone point to a doc that says this is a performance issue?

2 REPLIES
Cisco Employee

Re: Is a flapping mac address on a switch always a serious probl

1) When you get the MAC Address flapping, no traffic is forwarded to the MAC address for 15 seconds on the cat4k.

2) Cat6k doesn't display the MAC address flapping. If an etherchannel is misconfigured, yo uneed to fix it asap.

The following document talks about mac address flapping

www.cisco.com/warp/customer/473/62.shtml

Bronze

Re: Is a flapping mac address on a switch always a serious probl

1)Then how do they deal with this in wireless networks? I have not had any complaints and would think I would if devices stopped working for 15 seconds.

2) The link was about flapping HSRP. Isn't there a syslog or something I can turn on to se how much this is happening? I need ammo to interrupt processing and correct this. By the way, they told me they were setting the hosts up with IBMs High Availability "failover" feature. They did not say they were setting up channels. Thats why I set them up on separate cards for redundancy.

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