In fact it is applicable in physical networking too. Now the caveat is, when users are going to connect to this website, which address they are resolved to? Now there is interesting theory here. So every time, users are trying to connect to the website, they send traffic to the virtual MAC address of NLB cluster.
But this virtual MAC address is not physically connected on any switch. Since switch performs MAC learning in physical switch, virtual switch does not need to perform learning , this virtual MAC address of NLB cluster will not be recognised by switch during learning process as it is not connected physically to any switch. And it is not updated in MAC table.
So then, how the traffic gets delivered? This puts switch into a situation. Switch is forced to send the frames that are destined to NLB MAC address to all switch ports on the switch to make sure frames reach the correct destination. So basically Unicast mode forces switch flooding, where all switch ports are flooded with NLB traffic, even to the ports that are used by non-NLB cluster servers.
And as described above, switch is forced to send packets to all ports. This is true not only in virtual but physical networking environment as well. Ok that clears some air about these concepts. We can set these two policies to Accept or Reject. In standard switches, they are set to Accept by default however in DVS, they are set to Reject by default. What does these Accept and Reject setting mean? However, there are use cases as well where we do this intentionally. Take this example scenario below.
When any of the VMs attempt to talk to the outside network via the virtual ESXi network adapter, the virtual switch will check the source address of the Because the source address does not match the Effective Address of the virtual ESXi server, the frames will treated like a Forged Transmit and subsequently dropped. To protect against MAC address impersonation, all virtual switches will have forged transmissions set to reject. The hardware configuration page for the server appears.
Click the Configuration tab, and click Networking. Click Properties for the virtual switch whose layer 2 policy you want to review. Since Promiscuous Mode allows all traffic from the virtual switch to be visible on the configured portgroup, there is definitely going to be some amount of overhead when enabling this setting. If you drive a large amount of network traffic for your regular Virtual Machines, you may want to consider separating out your Nested ESXi environment.
I highly recommend you check out this blog post for the details. I've just setup a new nested environment. Will this prevent the probleme of the reduced network performance? If you have a two-level nested environment, make sure you only have one NIC enabled at the first level.
I found that by even using a standby adapter, packets got duplicated at this level despite that the second vmnic was in standby mode. By removing the standby adapter, the duplication of packets disappeared.
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