10-01-2017 07:35 AM - edited 03-05-2019 09:13 AM
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
10-02-2017 01:16 AM
10-03-2017 03:55 PM
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
10-05-2017 06:28 AM
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.
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