Re: SVI Interfaces has same MAC

Yes, I can tell you.
MAC addresses are expensive, especially if you purchase them on blocks of
millions, like Cisco does.
And because MAC addresses are really 24+24 bits, you can easily run out of
MAC addresses.

Before extended VLANs, most switching HW came with 1024 MAC addresses.
So if you bought a whole 24 bits of MAC addresses (I think it was $1000 even
in the 1980 - must be more expensive now)
You could produce 16384 devices. And we all know that addresses are not
allocated perfectly, so there's lots of overhead.

By reusing MAC addresses where you can, you reduce costs.

Fair enough?

On Tue, Oct 11, 2011 at 10:14 AM, CCIE KID <eliteccie_at_gmail.com> wrote:

> Hi fellas,
>
> Can anyone tell me the logic behind it . Why they use the same MAC address
> for all SVIs ? Is there any reason behind it
> Wat caveats can i expect if i see the same MAC address for al SVI's
>
> On Tue, Oct 11, 2011 at 1:13 PM, Lindsay Hill <lindsay.k.hill_at_gmail.com
> >wrote:
>
> > It depends a bit on the platforms - some use the same MAC, some change.
> >
> > Theoretically, it shouldn't matter - they're in different VLANs, so it
> > doesn't matter if the MAC address is the same, since the mac address
> table
> > takes into account the VLAN.
> >
> > Check out this link for a little more info and some examples:
> >
> http://cciepursuit.wordpress.com/2008/04/21/beware-the-man-of-one-platform/
> >
> > On 11/10/2011, at 7:50 PM, CCIE KID wrote:
> >
> > Here is the detail output
> >
> > R3(config-if)#do sh int vlan 10 | i address
> > Hardware is EtherSVI, address is c202.14d8.0000 (bia c202.14d8.0000)
> > Internet address is 10.1.1.3/24
> > R3(config-if)#
> > R3(config-if)#
> > R3(config-if)#do sh int vlan 20 | i address
> > Hardware is EtherSVI, address is c202.14d8.0000 (bia c202.14d8.0000)
> > Internet address is 20.1.1.3/24
> >
> >
> > Can anyone say why two different SVIs use same MAC address.
> >
> > On Tue, Oct 11, 2011 at 11:57 AM, CCIE KID <eliteccie_at_gmail.com> wrote:
> >
> > Hi fellas,
> >
> >
> > I find different SVI's has same MAC address .Like SVI for Vlan 10 and
> SVI
> >
> > for Vlan 20 has same virtual MAC address. I want to know the reason why
> > they
> >
> > both have same MAC address. Is there any reason behind it to do this kind
> > of
> >
> > design. This is my config
> >
> >
> > int vlan 10
> >
> > ip add 10.1.1.1 255.255.255.0
> >
> >
> > int vlan 20
> >
> > ip add 20.1.1.1 255.255.255.0
> >
> >
> > and I find same virtual MAC address when i do sh ip int vlan
> >
> >
> >
> >
> > --
> >
> > With Warmest Regards,
> >
> >
> > CCIE KID
> >
> > CCIE#29992 Security
> >
> >
> >
> >
> >
> > --
> > With Warmest Regards,
> >
> > CCIE KID
> > IN PURSUIT OF CCIE
> >
> >
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> >
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> >
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> >
> >
> >
> >
> >
> >
>
>
> --
> With Warmest Regards,
>
> CCIE KID
> IN PURSUIT OF CCIE
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
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-- 
Pavel Bykov
Blogs and organic groups at http://www.ccie.net