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  • 1.  Downsides to manually configuring an interface MAC address

    Posted 04-12-2019 13:30

    I'm in a situation where I need to set the Current address of one of my SRX interfaces to something other than the Hardware address. Does anyone know if there are any downsides/gotchas to doing this? Specifically, something like:

     

    set interfaces ge-0/0/0 mac <new_mac_here>

     

    Testing seems to show no ill effects so far. I haven't been able to find this statement in documentation yet, so I'm wondering about caveats to using it.



  • 2.  RE: Downsides to manually configuring an interface MAC address
    Best Answer

    Posted 04-12-2019 17:51

    Hi there,

     

    so this is what I know about the subject:

     

    -there is no problem internally as long as you don't duplicate the MAC for some reason

    -I have seen this done in troubleshooting doing it to accommodate the needs of certain implementations nothing bad really stands out

    -the new MAC assigned to the interface will survive reboots

    -the new MAC assigned to the interface will NOT survive an upgrade **you might need to be careful with this

     

    hope that helps a little!



  • 3.  RE: Downsides to manually configuring an interface MAC address

    Posted 04-15-2019 07:02

    Thanks, this was helpful!



  • 4.  RE: Downsides to manually configuring an interface MAC address

     
    Posted 04-12-2019 22:23

    What is connected to ge-0/0/0 interface, if its a switch or router, we just need to make sure the same MAC is not learned via any other interfaces on the connected switch/router.

     



  • 5.  RE: Downsides to manually configuring an interface MAC address

    Posted 04-13-2019 07:51

    Hello srx_admin,

     

    Just ensure that your MAC address is imaginary enough NOT to match any other vendor address and you would be fine.

     

    Best way to get this out of way is to use Locally Administered Address. 

     

    As per standard, the second bit of the first byte of a MAC address determines the type of OUI: -

     

    0 for globally assigned by the IEEE

    1 for locally administered MAC address.

     

    You can use the algorightm below to generate your own MAC address without any doubt of any other device matching it.

     

    Step-1:- Create a OUI number by whatever scheme you like, then logically OR it with 02:00:00:00:00:00.

    - This step will set bit#2 of the first byte.

     

    Step-2:- Now  logically AND it with fe:ff:ff:ff:ff:ff.

     - This step  clears bit#1 of the first byte (making it a unicast, not multicast address).

     

    If you are too lazy (like me) to do the MATH ,  simply use one of  the following set : -

     

    x2-xx-xx-xx-xx-xx
    x6-xx-xx-xx-xx-xx
    xA-xx-xx-xx-xx-xx
    xE-xx-xx-xx-xx-xx

     

    [You can fill 'x' with any possible HEX number ].

     

     

    Now all you would need to care about will be to "NOT assign the same "Locally Administered MAC" to any other device in the same network.

     

    I hope this one helps 🙂

     

    Thanks!