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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?
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 unique 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.
non-manage Switch?
Nov 11, 2018 at 4:08
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.
The MAC address used by the spanning tree algorithm (STA) implemented in a given switch does not belong to any of its Ethernet interfaces. At least in Cisco implementations, this MAC address is known as base MAC or universal (burned-in) MAC and its purpose is to identify the switch itself, not some of its Ethernet interfaces. For this reason, this MAC address is printed on a label attached on the back of the device.
You can check a device's base MAC by issuing the show version command:
SW1#show version Cisco IOS Software, C2960 Software (C2960-LANBASE-M), Version 12.2(25)FX, RELEASE SOFTWARE (fc1) Copyright (c) 1986-2005 by Cisco Systems, Inc. Compiled Wed 12-Oct-05 22:05 by pt_team
ROM: C2960 Boot Loader (C2960-HBOOT-M) Version 12.2(25r)FX, RELEASE SOFTWARE (fc4)
System returned to ROM by power-on
Cisco WS-C2960-24TT (RC32300) processor (revision C0) with 21039K bytes of memory.
24 FastEthernet/IEEE 802.3 interface(s) 2 Gigabit Ethernet/IEEE 802.3 interface(s)
63488K bytes of flash-simulated non-volatile configuration memory.
Base ethernet MAC Address : 0001.43BA.DE15
Motherboard assembly number : 73-9832-06 Power supply part number :
341-0097-02 Motherboard serial number : FOC103248MJ Power supply
serial number : DCA102133JA Model revision number : B0
Motherboard revision number : C0 Model number :
WS-C2960-24TT System serial number : FOC1033Z1EY Top
Assembly Part Number : 800-26671-02 Top Assembly Revision
Number : B0 Version ID : V02 CLEI Code Number : COM3K00BRA
Hardware Board Revision Number : 0x01
You can read more on this here
