Mac address static 0000.0000.0000 vlan X drop

[entertheleon]

Hello cisco experts. 

First of all, i am not native so my question isnt correct grammatically. Plz understand.

In our company Cisco L3 switch,

There are mac address-table static 0000.0000.0000 vlan X drop command.

I dont understand why this command should be set.

Plz let me know ...

This command means destination mac address 0000.0000.0000 drop. Right?

and it is different Arp request mac address right?

some explanation say this command protect arp attack. But arp request destination mac address  is ffff.ffff.ffff not 0000.0000.0000 right?

Our company L3 switches are using dhcp and eigrp and hsrp v1 and no ip proxy arp, no ip redirect and no ip unreachable etc.

Thank you a lot in advance.

[Flavio Miranda]

Hi

 You mean, the command was used this way  " address-table static 0000.0000.0000 " or are using zeros to represent the real mac address you see there?

[entertheleon]

I mean mac address-table static 0000.0000.0000 vlan 660 drop.

This command is set in c4507 switch.

I wanna know why this command has been set.

First, i expected it prevent arp attack but

Arp request message's mac address is ffff.ffff.ffff not 0000.0000.0000 right?

[Flavio Miranda]

 The command is wrong for sure and it does not have the functionality of prevent arp attack anyway. If you do the command  mac address-table static ffff.ffff.ffff vlan 660 drop, you can cause huge problem because any Layer2 broadcast will be dropped.

 This command is used to block a specific mac address from communicate on the network, that´s it used for.

So, lets say you want to block a mac address  aaaa.bbbb.cccc to communicate, you can use the command

mac address-table static aaaa.bbbb.ccc vlan 660 drop. Every time this machine try to send packets on the vlan 660 the switch will drop the packet or every time some mac address try to send packets to this mac address the switch will drop.

 Conclusion, this command as configured in the wrong way and is doing nothing.

[vazquez pc-01]

@Flavio Miranda 

And how can I remove the block? I mean after apply this command

#mac address-table static aaaa.bbbb.cccc vlan X drop

[MHM Cisco World]

I will try this in lab and inform you about the result 

MHM

[MHM Cisco World]

there is l2 security attack called IP theft and mac theft and mac/ip theft,  the character of this attack is using 0000.0000.0000 (as source or destination). 
so drop this mac is solution for this attack 

[Georg Pauwen]

Since we have AI, I thought I might as well use it and ask what ChatGTP thinks this all zeroes MAC address is being used for. Here is what AI says:

The MAC address `0000.0000.0000` is a special MAC address known as the "null" or "zero" MAC address. It is often used in certain networking contexts to signify various special conditions or functionalities. Here are some common use cases:

1. **Broadcast Address:** In some cases, this MAC address can be interpreted as a broadcast address, meaning it represents a frame sent to all devices on the network segment.

2. **Placeholder:** It can also serve as a placeholder or default value in configurations where a MAC address needs to be specified but isn't relevant.

3. **Ethernet Header Padding:** In certain networking protocols or situations, the all-zero MAC address can be used for padding or alignment purposes in Ethernet headers.

4. **Multicast Address:** While uncommon, some protocols may use the `0000.0000.0000` address as a multicast destination address.

5. **Error Handling:** It can be used in error handling scenarios where a MAC address is required but the actual address is not known or not relevant.

Overall, the `0000.0000.0000` MAC address is not assigned to any specific device and is typically used in a variety of special contexts within networking protocols and configurations.