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same MAC address in two mikrotik

Posted: Tue May 14, 2019 12:56 pm
by abubin
I just found out that there are 2 mikrotik sharing same MAC address. Probably from some cloning process that was done previously. My question is, both the devices are running live right now. Does running "reset-mac-address" command cause configurations rules to be reset as well? Will the whole network be brought down temporarily? Do I need to reboot the mikrotik?

Thanks.

Re: same MAC address in two mikrotik

Posted: Tue May 14, 2019 2:38 pm
by pe1chl
You can remove the MAC address but of course it causes a temporary problem on the network until everyone has noticed the new MAC address.
So do it outside office hours.

Re: same MAC address in two mikrotik

Posted: Wed May 15, 2019 5:17 am
by abubin
So does that means I have to run that command locally? I was thinking of changing the MAC remotely because the router is located in DC.

Also, please let me know if any of the mikrotik settings will be reset when I change the MAC addresses.

Another question is, should I change the MAC addresses one by one or should I just run the full reset command (/interface ethernet reset-mac-address)?

Thanks.

Re: same MAC address in two mikrotik

Posted: Wed May 15, 2019 7:48 am
by sindy
So does that means I have to run that command locally? I was thinking of changing the MAC remotely because the router is located in DC.
You can reset them remotely. What @pe1chl was telling you was that once a device talking to your Mikrotik via a given interface determines the MAC address of that interface (or a bridge behind it) using ARP, it stores that information for a while and uses it until it expires (or maybe until it is rewritten by a packet received from your Mikrotik which may not come spontaneously). So after the reset, until the ARP record times out and is re-created by ARP or until it is refreshed by an incoming packet, the IP packets will be sent to the old MAC address and thus effectively dropped.

So until the ARP records storing the old MAC addresses on all neighbour devices get renewed one way or the other, connections with these devices will be affected. It may take minutes in some cases; in the worst case there may be a static ARP record in some of the neighbouring devices which will have to be changed manually on that device.

Also, please let me know if any of the mikrotik settings will be reset when I change the MAC addresses.
It's rather a reverse question. Nothing but the MAC address itself will be changed on each interface, but If the ethernet interfaces are, directly or indirectly (via /interface vlan or /interface bonding, members of some bridges and some of those bridges have auto-mac set to no and some admin-mac configured, the MAC address of such bridges will not change even though you reset the MAC addresses of their member interfaces. In these cases the IP communication via each such bridge will not be interrupted until you manually change the admin-mac of that bridge. Where auto-mac=yes (the default), the bridge (and also all /interface vlan which have that bridge as a carrier interface) inherits its MAC address from the member port with the lowest numeric value of MAC address so it will change as you reset it on the member interface. Same case with /interface bonding which also inherits MAC from member interfaces.

Another question is, should I change the MAC addresses one by one or should I just run the full reset command (/interface ethernet reset-mac-address)?
To minimize the outage I'd recommed to change all interfaces in a single step; to do that, you need to add [find] to the end of the command instead of interface name.

Re: same MAC address in two mikrotik

Posted: Wed May 15, 2019 2:31 pm
by mkx
I just found out that there are 2 mikrotik sharing same MAC address.

If those devices are not in the same network (i.e. there's at least one or preferably two routers between them), then they should not interfere with each other ... in that case it's no hurry to reset MAC addresses.

Re: same MAC address in two mikrotik

Posted: Thu May 23, 2019 1:27 pm
by abubin
To minimize the outage I'd recommed to change all interfaces in a single step; to do that, you need to add [find] to the end of the command instead of interface name.
Can I know what is the exact command I should use with [find] command? Sorry, I can't find any reference for this on changing MAC addresses and my mikrotik CLI skill is still very noob. Thanks in advance.

If those devices are not in the same network (i.e. there's at least one or preferably two routers between them), then they should not interfere with each other ... in that case it's no hurry to reset MAC addresses.
It does somewhat interfere as both the routers have some sort of connection between them. Though there is nothing major yet in terms of network but I would like to resolve them before problem arises.

Re: same MAC address in two mikrotik

Posted: Thu May 23, 2019 2:38 pm
by sindy
To minimize the outage I'd recommed to change all interfaces in a single step; to do that, you need to add [find] to the end of the command instead of interface name.
Can I know what is the exact command I should use with [find] command? Sorry, I can't find any reference for this on changing MAC addresses and my mikrotik CLI skill is still very noob. Thanks in advance.
It was meant exactly as it was written, just [find]. Without any parameters, find matches all elements of the configuration subtree within which it is used, so it produces a list of all interface IDs for the outer command.