Does virtual Interface have MAC address ?

[jai.s401]

1.when entering the cmd " sh ip arp" The Ip- mac address mapping will display.

Is it the MAC address of the Cisco Device or the Port/interface or the end point (user machine's MAC) ??

2.How to view MAC address of a cisco device?

3.Does a Interface VLAN will have MAC address. ?

[Martin L · Accepted solution]

Cisco devices come out with some range of MACs reserved for particular device starting with main MAC of device and growing up sequentially.  This is so you can add a virtual interface to a device, in which case, a MAC is assigned from that reserved pool.  To see MAC assigned to interface Use show interface command.  To see main MAC of a device -so called Burn-In MAC (BIA), use show version command.  Interface Loopback does not have MAC assigned. not sure why; must be something else to track it. 

show ip arp shows both MACs of remote device and local ones.  When you see a dash symbol ( - ) under Age in the output of show ip arp command, it means that MAC is at local device; while any other number represents time: starting at 0 minutes.  

Regards, ML
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[jai.s401]

Are the SVI and Loopback Interface are One and the same ?

[Martin L]

No, IP of a Loopback interface is mostly used as router id since loopback interfaces never go down while SVI is used for routing traffic on switches and special routers (those with switching modules) and SVI can go down. You can set up L3 switch to route its vlan traffic with SVI interfaces.  L2 switch can only have 1 SVI up up state to route remote traffic to/from that switch.   There are other used for Loopbacks that you can see at expert level of networking.

Regards, ML
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[Giuseppe Larosa]

Hello @jai.s401 ,

they are different .

Both are logical interfaces but:

a loopback interface has no relationship with other interfaces it is up/up until the node router or switch is alive.

Loopback are useful to represent a L3 node either a router or a switch in routing protocols or for management purposes.

An SVI interface VLAN is up/up only if:

the associated layer2 VLAN / broadcast domain exists in the VLAN database and it is active

and at least one L2 port associated to the L2 VLAN is up/up and in STP forwarding state  ( this is called autostate)

So an SVI is a logical interface but its status depends on the physical interfaces of the switch associated to the VLAN.

This is reasonable as the SVI most of the times act as default gateeway for the VLAN if the SVI is up/up even when there is no available exit interface at L2 it would a black hole for the entire IP subnet.

Hope to help

Giuseppe