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I saw a post say Switch do not need its MAC address, unless it's an administrable Switch for managing.

but I found the spanning-tree protocol need a MAC address of Switch to form STP Root Bridge ID.

so, is the switch always need a MAC address? nevertheless in a two layer circuit, all the Switch need a self MAC address at least?

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    On Cisco, all interfaces including SVI's have burned in MAC addresses. – user36472 Nov 9 '18 at 12:45
  • @Cown I mean, except the interfaces and SVI, is the Switch still need MAC address? – three-blocks Nov 11 '18 at 4:01
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The basic function of a switch is transparent bridging - for this, it doesn't need any MAC address of its own.

However, if you need to talk to a switch - ie. a managed switch - then that switch requires an address; usually that is a MAC address and an IP address [*]. STP is only supported on managed switches and in addition, an STP bridge is required to have a bridge ID which usually is identical to the management MAC address.

[*] A managed network device could just have a serial console which doesn't require any addressing. However, this was only used on very early devices. Today, most devices feature both, in-band network management and out-of-band console access.

  • I have a question, in a switch STP circuit, can there have a non-manage Switch? – three-blocks Nov 11 '18 at 4:08
  • Theoretically yes, but I have never seen an unmanaged switch supporting STP. Without a console, you wouldn't be able to set the STP priorities. With STP, that unmanaged switch would be required to have a MAC address as well. – Zac67 Nov 11 '18 at 8:17
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Yes, if your switch supports spanning-tree protocol(either legacy spanning tree protocol, rapid-pvst+ or MST) your switch will have a mac address since spanning-tree protocol uses bridgeID to elect the root bridge and bridgeID consists of the bridge-Priority, a unique mac address and system-id which is basically the vlan number.

Also if a switch has a management ip address, it will need to have a mac address so that ethernet frames can be forwarded to it at layer 2.

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