Vlan – Why does it show duplicate mac addresses in same VLAN

vlan

 6509 Server-VSS Switch Rack GG 10.36.x.x

I checked show mac-address-table interface port-channel 133
shows duplicate mac address:

* 2301  0050.5617.07a0   dynamic  Yes        175   Po133
* 2301  0050.5617.07a0   dynamic  Yes         45   Po133
* 2301  0050.5617.07a2   dynamic  Yes         40   Po133
* 2301  0050.5617.07a2   dynamic  Yes        215   Po133
* 2301  0050.5617.1000   dynamic  Yes         10   Po133
* 2301  0050.5617.1000   dynamic  Yes        130   Po133
* 2301  0050.5617.1002   dynamic  Yes         10   Po133
* 2301  0050.5617.1002   dynamic  Yes        130   Po133
* 2301  0050.5617.1540   dynamic  Yes         50   Po133
* 2301  0050.5617.1540   dynamic  Yes        130   Po133
* 2301  0050.5617.1542   dynamic  Yes         50   Po133
* 2301  0050.5617.1542   dynamic  Yes         75   Po133
* 2301  0050.5617.1cc0   dynamic  Yes         10   Po133
* 2301  0050.5617.1cc0   dynamic  Yes        210   Po133
* 2301  0050.5617.1cc2   dynamic  Yes          5   Po133
* 2301  0050.5617.1cc2   dynamic  Yes        215   Po133
* 2301  0050.5617.2660   dynamic  Yes         55   Po133
* 2301  0050.5617.2660   dynamic  Yes         75   Po133
* 2301  0050.5617.2662   dynamic  Yes         55   Po133
* 2301  0050.5617.2662   dynamic  Yes         75   Po133
* 2301  0050.5617.2820   dynamic  Yes          5   Po133
* 2301  0050.5617.2820   dynamic  Yes        130   Po133
* 2301  0050.5617.2822   dynamic  Yes          5   Po133
* 2301  0050.5617.2822   dynamic  Yes        130   Po133
* 2301  0050.5617.37e0   dynamic  Yes         45   Po133
* 2301  0050.5617.37e0   dynamic  Yes        210   Po133
* 2301  0050.5617.37e2   dynamic  Yes         45   Po133
* 2301  0050.5617.37e2   dynamic  Yes        185   Po133
* 2301  0050.5617.3cc0   dynamic  Yes         40   Po133
* 2301  0050.5617.3cc0   dynamic  Yes        130   Po133
* 2301  0050.5617.3cc2   dynamic  Yes         40   Po133
* 2301  0050.5617.3cc2   dynamic  Yes         75   Po133
* 2301  0050.5617.3f40   dynamic  Yes         50   Po133
* 2301  0050.5617.3f40   dynamic  Yes         75   Po133
* 2301  0050.5617.4320   dynamic  Yes         25   Po133
* 2301  0050.5617.4320   dynamic  Yes        130   Po133
* 2301  0050.5617.4322   dynamic  Yes         45   Po133
* 2301  0050.5617.4322   dynamic  Yes         75   Po133
* 2301  0050.5617.43a0   dynamic  Yes         25   Po133
* 2301  0050.5617.43a0   dynamic  Yes        130   Po133
* 2301  0050.5617.43a2   dynamic  Yes         20   Po133
* 2301  0050.5617.43a2   dynamic  Yes         75   Po133
* 2301  0050.5617.44e0   dynamic  Yes         30   Po133
* 2301  0050.5617.44e0   dynamic  Yes        215   Po133
* 2301  0050.5617.44e2   dynamic  Yes         25   Po133
* 2301  0050.5617.44e2   dynamic  Yes        215   Po133
* 2301  0050.5617.4780   dynamic  Yes         55   Po133
* 2301  0050.5617.4780   dynamic  Yes        215   Po133
* 2301  0050.5617.4782   dynamic  Yes         55   Po133
* 2301  0050.5617.4782   dynamic  Yes        210   Po133
* 2301  0050.5617.4ca0   dynamic  Yes         55   Po133
* 2301  0050.5617.4ca0   dynamic  Yes        130   Po133
* 2301  0050.5617.4ca2   dynamic  Yes         55   Po133
* 2301  0050.5617.4ca2   dynamic  Yes        130   Po133
* 2301  0050.5617.51e0   dynamic  Yes         35   Po133
* 2301  0050.5617.51e0   dynamic  Yes         75   Po133
* 2301  0050.5617.51e2   dynamic  Yes         35   Po133
* 2301  0050.5617.51e2   dynamic  Yes         75   Po133
* 2301  0050.5617.5260   dynamic  Yes          0   Po133
* 2301  0050.5617.5260   dynamic  Yes        130   Po133
* 2301  0050.5617.5262   dynamic  Yes          0   Po133
* 2301  0050.5617.5262   dynamic  Yes        130   Po133
* 2301  0050.5617.5880   dynamic  Yes         15   Po133
* 2301  0050.5617.5880   dynamic  Yes        215   Po133
* 2301  0050.5617.5882   dynamic  Yes         20   Po133
* 2301  0050.5617.5882   dynamic  Yes        180   Po133
* 2301  0050.5617.5a60   dynamic  Yes         20   Po133
* 2301  0050.5617.5a60   dynamic  Yes        130   Po133
* 2301  0050.5617.5a62   dynamic  Yes         20   Po133
* 2301  0050.5617.5a62   dynamic  Yes        130   Po133
r-tx-server-1#show interfaces status | inc 2301
Gi1/2/11     *** MediaSite Vide notconnect   2301         full   auto 10/100/1000BaseT
Gi1/3/9      *** Culinary Video notconnect   2301         full   auto 10/100/1000BaseT
Gi1/3/28     *** Culinary Video notconnect   2301         full   auto 10/100/1000BaseT
Gi1/4/1      *** MEDIALX - E291 notconnect   2301         full   auto 10/100/1000BaseT
Gi1/4/3      *** FACULTYWEB - E notconnect   2301         full   auto 10/100/1000BaseT
Gi1/4/17     ***FACULTYWEB - S3 notconnect   2301         full   auto 10/100/1000BaseT
Gi2/2/13     ** EMSDVCS1  **    connected    2301       a-full a-1000 10/100/1000BaseT
Gi2/2/14     ** EMSDVCS2  **    connected    2301       a-full a-1000 10/100/1000BaseT
Gi2/2/15     ** EMSDVCS3  **    connected    2301       a-full a-1000 10/100/1000BaseT
Gi2/2/16     ** EMSIISSQL **    connected    2301       a-full a-1000 10/100/1000BaseT
Gi2/2/17     ** EMSDVCS4  **    connected    2301       a-full a-1000 10/100/1000BaseT
Gi2/2/18     ** EMSDVCS5  **    connected    2301       a-full a-1000 10/100/1000BaseT
Gi2/2/21     *** ICHAIN ***     notconnect   2301         auto   auto 10/100/1000BaseT
r-tx-server-1#show arp | inc Incomplete
Internet  10.21.1.21              0   Incomplete      ARPA
Internet  10.23.1.58              0   Incomplete      ARPA
Internet  10.20.254.200           0   Incomplete      ARPA
Internet  10.23.1.54              0   Incomplete      ARPA
Internet  10.20.254.202           0   Incomplete      ARPA
Internet  10.33.3.21              0   Incomplete      ARPA
Internet  10.34.1.20              0   Incomplete      ARPA
Internet  10.41.0.29              0   Incomplete      ARPA
Internet  198.150.241.240         0   Incomplete      ARPA
Internet  10.35.1.116             0   Incomplete      ARPA
Internet  10.39.0.115             0   Incomplete      ARPA
Internet  10.23.100.11            0   Incomplete      ARPA
Internet  10.199.0.12             0   Incomplete      ARPA
Internet  10.39.0.202             0   Incomplete      ARPA
Internet  10.199.0.53             0   Incomplete      ARPA
Internet  10.20.251.30            0   Incomplete      ARPA

My question is why are the IP addresses incomplete?

Best Answer

My question is why are the IP addresses incomplete?

An ARP entry is marked as incomplete when the device in question (in this case your switch) can't get an ARP response from the host.

This generally means that host IP doesn't exist, or you are filtering ARP responses on either the host (generally difficult to do), or on the switch (eg: using a VLAN access-map and blocking the ARP Ethertype).

If your switch is L3 (eg: it is routing to each of those subnets), then it may be that devices elsewhere in your network are trying to reach them, and while the switch has the subnet locally attached to it, it cannot resolve ARP and work out the destination MAC.

Why does it show duplicate mac addresses in same VLAN?

I could be wrong, but I think VLAN ID is in the second last column of your output, in which case, you have a bunch of different VLANs all trunked on Po133 and you are just seeing the same MAC in multiple VLANs (which is perfectly legitimate.

Keep in mind that ARP Tables and MAC-address-tables are two very different things - one relates to routing (L3), and one to switching (L2).

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