Technical FAQs

certforumz · March 29, 2014, 03:25:10 AM

Bit.Decoder wrote:

Hi,

Does routers have a single unique MAC address or does each of its interface have a unique physical address. I ask this because when the router gets bits coming in into its interfaces, it arranges them into frames and goes ahead to read the layer 2 header. So there must be a reference MAC address/addresses on the router which it uses to discriminate if the frame belongs to the router or not. Many Thanks

Kind Regards,

Bit

Great question-

The MAC address of each Ethernet interface, has its own assigned MAC address.

If we create Ethernet sub-interfaces, each sub-interface inherits the MAC address of the parent physical interface.

If we configure the MAC address, (instead of using the Burned In Address (bia)), then the Ethernet sub-interfaces, if any, will inherit those same MAC addresses.

R2#show run | section interface

interface FastEthernet0/0

ip address 10.0.0.2 255.255.255.0

interface FastEthernet0/1

no ip address

interface FastEthernet0/1.10

encapsulation dot1Q 10

ip address 23.0.0.2 255.255.255.0

interface FastEthernet0/1.20

encapsulation dot1Q 20

ip address 24.0.0.2 255.255.255.0

R2#show interface | inc Fast|bia

FastEthernet0/0 is up, line protocol is up

Hardware is Gt96k FE, address is c203.015d.0000 (bia c203.015d.0000)

FastEthernet0/1 is up, line protocol is up

Hardware is Gt96k FE, address is c203.015d.0001 (bia c203.015d.0001)

FastEthernet0/1.10 is up, line protocol is up

Hardware is Gt96k FE, address is c203.015d.0001 (bia c203.015d.0001)

FastEthernet0/1.20 is up, line protocol is up

Hardware is Gt96k FE, address is c203.015d.0001 (bia c203.015d.0001)

R2#show ip arp

Protocol Address Age (min) Hardware Addr Type Interface

Internet 10.0.0.2 - c203.015d.0000 ARPA FastEthernet0/0

Internet 23.0.0.2 - c203.015d.0001 ARPA FastEthernet0/1.10

Internet 24.0.0.2 - c203.015d.0001 ARPA FastEthernet0/1.20

R2#

Best wishes,

Keith

Technical FAQs

certforumz