https://community.extremenetworks.com/t5/network-architecture-design/duplicated-macs-on-different-vlans-on-same-switched-infra/m-p/13025#M429 Just one point, to have same mac on many vlans can be perfectly OK, the decision about "what mac to the need to send this IP packet to " is a per vlan question, not a network one. For example some vendors ( I know checkpoint do this ) you will see the same mac for every vlan for the same physical interface, for the checkpoint gateway. Of course if someone had connected one vlan to another like users sometimes do with edge points that's not so good. <BR /> <BR /> Mon, 22 May 2017 11:24:00 GMT simon_bingham 2017-05-22T11:24:00Z https://community.extremenetworks.com/t5/network-architecture-design/duplicated-macs-on-different-vlans-on-same-switched-infra/m-p/13023#M427 My network includes more than hundred of switches in multiple-ring design ..<BR /> when issuing: show iparp<BR /> I am finding rejected IP .. I believe it doesn't has anything to do with the duplication ...<BR /> But I wanna be sure that I have no duplicated MACs on my network so...<BR /> <BR /> - Does duplicated MACs on different VLANs on Same switched infra cause problems?<BR /> - How to find duplicated MACs on different VLANs on Same switched infra?<BR /> <BR /> Thanks<BR /> Yusuf Sun, 21 May 2017 19:09:00 GMT https://community.extremenetworks.com/t5/network-architecture-design/duplicated-macs-on-different-vlans-on-same-switched-infra/m-p/13023#M427 Yusuf_Kabbara 2017-05-21T19:09:00Z https://community.extremenetworks.com/t5/network-architecture-design/duplicated-macs-on-different-vlans-on-same-switched-infra/m-p/13024#M428 Hi Yusuf, I think it will give you ARP poison like problem since FDB maps each MAC to a port. Actually, I haven't tried that case. You should test it on separate switch to make sure. Best regards, Sun, 21 May 2017 19:23:00 GMT https://community.extremenetworks.com/t5/network-architecture-design/duplicated-macs-on-different-vlans-on-same-switched-infra/m-p/13024#M428 Mrxlazuardin 2017-05-21T19:23:00Z https://community.extremenetworks.com/t5/network-architecture-design/duplicated-macs-on-different-vlans-on-same-switched-infra/m-p/13025#M429 Just one point, to have same mac on many vlans can be perfectly OK, the decision about "what mac to the need to send this IP packet to " is a per vlan question, not a network one. For example some vendors ( I know checkpoint do this ) you will see the same mac for every vlan for the same physical interface, for the checkpoint gateway. Of course if someone had connected one vlan to another like users sometimes do with edge points that's not so good. <BR /> <BR /> Mon, 22 May 2017 11:24:00 GMT https://community.extremenetworks.com/t5/network-architecture-design/duplicated-macs-on-different-vlans-on-same-switched-infra/m-p/13025#M429 simon_bingham 2017-05-22T11:24:00Z https://community.extremenetworks.com/t5/network-architecture-design/duplicated-macs-on-different-vlans-on-same-switched-infra/m-p/13026#M430 <U></U>The same MAC can be on multiple VLANs because a MAC is not routed off the VLAN, rather, the router builds a new packet with its MAC before transmitting another VLAN. Some routers have the same MAC on multiple interfaces. Net sight’s compass could be used to find duplicate MAC's.<BR /> <BR /> <BR /> <BR /> Mon, 22 May 2017 11:24:00 GMT https://community.extremenetworks.com/t5/network-architecture-design/duplicated-macs-on-different-vlans-on-same-switched-infra/m-p/13026#M430 Luke_French 2017-05-22T11:24:00Z https://community.extremenetworks.com/t5/network-architecture-design/duplicated-macs-on-different-vlans-on-same-switched-infra/m-p/13027#M431 Interesting, I wonder how FDB table will be shown on that case. Mon, 22 May 2017 11:24:00 GMT https://community.extremenetworks.com/t5/network-architecture-design/duplicated-macs-on-different-vlans-on-same-switched-infra/m-p/13027#M431 Mrxlazuardin 2017-05-22T11:24:00Z https://community.extremenetworks.com/t5/network-architecture-design/duplicated-macs-on-different-vlans-on-same-switched-infra/m-p/13028#M432 The FDB is populated per VLAN, so you will see multiple entries for the MAC in each VLAN that it exists in. Mon, 22 May 2017 11:24:00 GMT https://community.extremenetworks.com/t5/network-architecture-design/duplicated-macs-on-different-vlans-on-same-switched-infra/m-p/13028#M432 BrandonC 2017-05-22T11:24:00Z