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a burst of RTD-1-ADDR_FLAP messages ????


Has anyone ever seen a problem that could cause a burst of MAC address re-learning ?

We have twice experienced a problem where portions of the network go very slow (apps timeout etc), with many of our switches reporting RTD-1-ADDR_FLAP messages. The messages come from several switches, all within the same VLAN. The specific ports that are re-learning include both inter-switch links (not ISL or .1p 'trunks') and single server ports.

Our general network topology is a core 6500 with links to stacks of 3500XL and 2950 switches. All of the messages came from 3500s, none from the 2950s or the 6500.

Although I cannot guarantee that nobody is messing with the topology, I don't think that any loops are being created (for the most part folks around here get me to do all of the layer 1-2-3 work so they can blame their layer 7 problems on me :).

The problem lasts for 20 minutes or so, and has cleared itself. Any ideas as to what might cause this ?

Thanks in advance for any comments.

Best Regards,



Re: a burst of RTD-1-ADDR_FLAP messages ????

This message means that the switch is learning the same mac address on multiple ports. When the same mac-address is learned again on the same port from a different destination port the error message is seen.This could be possibly due to a device with dual NIC present on one of the switch ports or due to a bridging loop that comes from a port that should block, instead it is forwarding traffic. Here's what the documentation says about this message.

Message: ADDR_FLAP, RTD, LOG_ALERT, 0, "%s relearning %d addrs per min

Explanation: Normally, MAC addresses are learned once on a port. Occasionally, when a switched network reconfigures, due to either manual or STP reconfiguration, addresses learned on one port are relearned on a different port. However, if there is a port anywhere in the switched domain that is looped back to itself, addresses will jump back and forth between the real port and the port that is in the path to the looped back port. Also refer to the documentation at: