MAC ADDRESS TABLE

[Piwo]

Hello Gents,

Would like to have your support to understand the following content of a MAC ADD Table for SW1.

I have 3 switches interconnected with trunk links : SW3 (with a native Vlan 99, ip 192.68.1.3) - SW2 (with a native Vlan 99, ip 192.68.1.2) - SW1 (with a native Vlan 99, ip 192.68.1.1) .

Port Connections :

SW3 F0/1 - SW2 GI0/1   SW2 GI0/2 - SW1 GI0/2   SW1 GI0/3 - SW3 F0/3

Question :What are those mac address below and some of them are not even in ARP table ?

I would like to understand the content of the MAC table for the different VLANS.

Switch1#show mac add dynamic

   1    0013.c3da.39c3    DYNAMIC     Gi0/3
  99    0013.c3da.39c0    DYNAMIC     Gi0/3
  99    0013.c3da.39c3    DYNAMIC     Gi0/3
  99    0019.aa91.d341    DYNAMIC     Gi0/3
Total Mac Addresses for this criterion: 4
Switch1#show ip arp
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  192.168.1.1             -   0019.e86d.be41  ARPA   Vlan99
Internet  192.168.1.3            33   0013.c3da.39c0  ARPA   Vlan99
Internet  192.168.1.2             0   0019.aa91.d341  ARPA   Vlan99

Thank you

[Mark Malone]

Hi
there Cisco mac address they belong to them , 0013C3 is the vendor part of the MAC OUI
0013C3 Cisco Systems, Inc

They must be assigned to an interface some where as system macs

[Piwo]

Hi Mark,

Thanks for your reply.

That s clear for me, But i still have doubts regarding thsi topic.

Maybe you can support :)

Doubt:

I have just 3 switches interconnected without any clients, I know these Dynamic addresses belong to STP BPDUs messages exchanged. This is what is confusing me, how this dynamic address are built in the MAC Table.

Switch1#show mac add dynamic

   1    0013.c3da.39c3    DYNAMIC     Gi0/3
  99    0013.c3da.39c0    DYNAMIC     Gi0/3
  99    0013.c3da.39c3    DYNAMIC     Gi0/3
  99    0019.aa91.d341    DYNAMIC     Gi0/3

[Moses Fernandes]

Hello,

I'm not a genius. I'm just trying to answer a query to best of my understanding.

sh arp -  will only display the IPs to which the router/switch/PC Resolves (know) its mac address.(Simple words)

ARP establishes correspondences between network addresses (an IP address, for example) and Ethernet hardware addresses. A record of each correspondence is kept in a cache for a predetermined amount of time and then discarded.(Cisco Jargon).

show mac add - will display the mac addresses that it has learnt. Again its only learnt mac addresses and necessary not connected to the switch itself. It also has keeps a track of learnt mac addresses via which port. This helps it in forwarding frame a bit faster.

Also I assume that they work of different layer.

MAC Address table is a layer 2 protocol.

APR is layer 3 protocol.

Hope its helpful.

Regards,

Moses.