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Switch Multicast message

Been getting this message on 4000 & 5000 switches constantly, Cannot determine the MAC (45;00:???) and the port, 5/58. There is no 5/58...Any insight would be greatly appreciated.

%SYS-4-P2_WARN: 5/Invalid traffic from multicast source ad

dress 45:00:00:5b:7a:c1 on port 5/58

Community Member

Re: Switch Multicast message


Check out TAC error message decoder at:

1. %SYS-4-P2_WARN: Host [mac addr] is flapping between port [dec/dec] and port [dec/dec]

The above message indicates that your Catalyst 4000 switch has learned a MAC address that already exists in its CAM table on a port other than the original one.

Recommended Action: What you need to do is to track down how this MAC address was learned from both ports.

Step 1: Consider port the first port. Issue the show cam dynamic [port] command. If you see the MAC address 00:50:0f:20:08:00 coming out in the list of the MAC addresses learned on this port, try to see if this is a single host that is connected or if there are multiple hosts registered on that port.

Step 2: If it is a single host that is connected, check the other port that is registered and see if the host is dually attached to the switch. If however, the host has connections to other devices that can eventually lead back into this switch, try to track down the intermediate devices that are in between.

Note: The best way to achieve this (assuming that they are Cisco devices) is to use the output of the command show cdp neighbors detail.

Related document:

Cisco - Common CatOS Error Messages on Cisco Catalyst ...

2. %SYS-4-P2_WARN: Filtering Ethernet MAC address of value zero

The "Filtering Ethernet MAC address of value zero" syslog message is generated when the switch receives packets with a source MAC address of 00-00-00-00-00-00, which is an invalid source MAC.

Recommended Action: The syslog message indicates that the switch is refusing to learn the invalid address. However, the switch will forward traffic sourced from an all zeros MAC address. Try to identify the end station that is generating frames with an all 0's source MAC address. Typically, such frames are transmitted from a traffic generator (for example, SmartBits), certain types of servers (such as load balancing IBM WebSphere servers), a misconfigured router or end station (for example, a device transmitting all 0's broadcasts), or a faulty NIC.

Related document:

Cisco - Common CatOS Error Messages on Cisco Catalyst

Community Member

Re: Switch Multicast message

Thanks for your help... exactly what I was looking for.


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