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I see in arp table only MACs and Vlans pairs. I have 3 ports is in same Vlan in access mode ( vlan is configured as interface with ip address and routing ), my question is if packets routed to this vlan/subnet are sended to all associated ports? Or only to port where destionation IP is connected. In route table is destionation network and mentioned vlan. I quess that yes, because destination ip is nowhere associated with port where can be reached.

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Switches usually don't know anything about IP addresses. They only keep a table with MAC addresses and the ports where they are located. Even if they use VLANs, they still just use MAC-port combination in their tables, and don't use IP's at all.

If it has the mac in the mac table, it sends only to the port where that mac is located. If it doesn't (yet) know the mac/port association, it broadcasts the packet out through all ports in that VLAN.

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I'm talking about router, no L2 switch. Destination MAC is in CAM table. Maybe I'm confused with ARP table, but I think that if destination IP host is directly connected to one of these 3 ports, and no MAC - IP association is in ARP talbe and route is assciated to vlan, that the packet is send to all 3 ports. – tombo Jun 9 '12 at 5:29
It has to know the mac of the pc it's sending the packet. Before sending the packet, it will do an arp resolution (broadcast over the whole vlan for that subnet, and then a response, and then send an ethernet packet with the correct destination mac. The broadcast is sent to all interfaces in that vlan. When the pc responds (with his mac), his mac is stored in the mac table, and the device knows which port to use to send the packet. After some time, when the mac table expires, all packets with "unknown" mac addresses are first sent out of all intarfaces in that vlan. – mulaz Jun 9 '12 at 5:57
@tombo I think you're confusing layers 2 and 3. A frame will flood all ports if a destination MAC isn't in the switch's table, but if ARP resolution fails then the packet won't be sent to the broadcast MAC - it'll fail to forward into the subnet. So, the scenario you're describing will not result in flooding - but the reverse scenario will. – Shane Madden Jun 9 '12 at 19:55

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