[c-nsp] Cat3750: MAC addresses of L3 interfaces change after reboot ?!

[Marian Ďurkovič]

Well it seems MAC address can't be configured on this platform, at least not
via the usual "mac-address xxxx.xxxx.xxxx" command.

But according to this:

https://supportforums.cisco.com/document/7816/mac-addresses-used-cisco-3750

the switch always uses the same MAC address for 64-th L3 interface and above,
so the very ugly workaround might be to create 63 dummy VLAN interfaces to
consume the whole MAC address pool and use e.g. vlan 100 and above for real
L3 interfaces...


   M. 


On Sat, 11 Oct 2014 12:36:04 +0100, Tom Storey wrote
> What if you were to create an L3 interface, then get the MAC address
> of that interface as generated by the system, then configure that MAC
> address on the interface so it doesnt change across reboots?
> 
> On 8 October 2014 08:02, Marian Ďurkovič <md at bts.sk> wrote:
> > Hi all,
> >
> >
> >   Catalyst 3560/3750 /G/E switches seem to implement L3 interfaces differently
> > than other switches - they use unique MAC address per every L3 interface.
> >
> >   MAC addresses are assigned from the MACaddr pool in the order how L3
> > interfaces are created, however after reboot they are assigned differently
> > - in the order how interfaces appear in the config.
> >
> >   As an example, if you add "no switchport" to interface Gig0/1 as the last
> > change, it might get xxxx.xxxx.07c7 MAC address from the pool, but after reboot,
> > it gets xxxx.xxxx.07c1 and all other L3 interfaces get higher MAC addresses than
> > before.
> >
> >   This creates serious problems in environments where strict MAC address
> > security is needed - since manual intervention is required to restore network
> > connectivity.
> >
> >   Is there any way to change this odd behavior on Cat 3560/3750 by e.g.
> >
> > - making the switch use the same MAC address for all L3 interfaces
> > - making the switch reuse the same MAC addresses after reboot (MAC persistence)
> > - configuring the MAC address on L3 interface manually?
> >
> >
> >     Thanks & kind regards,
> >
> >         M.
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