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1. #WHY DO CISCO MAC ADDRESS TABLE DROP HOW TO#
2. #WHY DO CISCO MAC ADDRESS TABLE DROP UPDATE#
3. #WHY DO CISCO MAC ADDRESS TABLE DROP SOFTWARE#

The destination IP address must be a PC2 IP address but here it has PC1 IP address, so it will drop the packet. At layer 3, it will check the destination IP address. Since it’s broadcast MAC address, it will accept and send to Layer 3. PC2 also receives the packet, and it will check the destination MAC address first. MAC Address Table Switch#show mac-address-table Now, if you run the command in Switch, you will see PC1 MAC-address entry in MAC address table.

#WHY DO CISCO MAC ADDRESS TABLE DROP UPDATE#

The switch receives the packet, and it will learn the MAC address of the PC1, and it will update in the MAC address table. Since it’s a broadcast frame, it will be flooded to the network.

It immediately generates an ARP packet with broadcast destination mac address and destination IP address with its own IP address 192.168.0.1.Īlso note that, in this packet, you can see the PC1 source MAC address and source IP address. MAC Address table Switch#show mac-address-table So there is no chance of learning PC MAC address by a switch.Īt this point, when we run the command in switch, then you will see no entry in the MAC address table. Even if the PC1 mac address is static, as soon as you disconnect the cable from that port or you shutdown the port that mac address will get flushed from the mac address table, and even if you will still have that mac address in the configuration under the secured port it would not mean that the switch will keep it in its mac address table once it is disconnected. So it will drop the frames and never send back a reply switch.

#WHY DO CISCO MAC ADDRESS TABLE DROP HOW TO#

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#WHY DO CISCO MAC ADDRESS TABLE DROP SOFTWARE#

I suspect the root cause of the invalid source mac addresses could be a faulty nic, a software bug or perhaps a misconfigured vmware server. From my reading, other platforms (2960, 3750, etc) seem to forward the frames along but don't log them as invalid, nor do they add an entry to the mac address-table. After a bit of googling it appears the 4500 is the only cisco platform which logs invalid source mac addresses. It in turn is connected to 6 other access switches. The device connected to Te5/1 is an access switch (Cisco 3750). Recently i've noticed serror messages on the 4500 which indicate frames have been received with an invalid source mac address: Not all access switches are directly connected to the 4500 - there is some daisy chaining of switches which was apparently done as a result of inadequate cabling. I have inherited support of a remote site which contains a Cisco 4500 and is connected to ~2 dozen cisco access switches - primarily 2960s with a couple of 3750s and 3560s.