Dell S3048-ON, Configuration Manual

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With Multicast NLB mode, the data forwards to all the servers based on the port specified using the following Layer 2 multicast command
in CONFIGURATION MODE:
mac-address-table static <multicast_mac> multicast vlan <vlan_id> output-range <port1>, <port2>
Limitations of the NLB Feature
The following limitations apply to switches on which you configure NLB:
• The NLB Unicast mode uses switch flooding to transmit all packets to all the servers that are part of the VLAN. When a large volume of
traffic is processed, the clustering performance might be impacted in a small way. This limitation is applicable to switches that perform
unicast flooding in the software.
• The
ip vlan-flooding
command applies globally across the system and for all VLANs. In cases where NLB is applicable and ARP
replies contain a discrepancy in the Ethernet SHA and ARP header SHA frames, a flooding of packets over the relevant VLAN occurs.
• The maximum number of concurrent clusters that is supported is eight.
Microsoft Clustering
To provide transparent failover or balancing, Microsoft clustering allows multiple servers using Microsoft Windows to be represented by one
MAC address and IP address. The Dell Networking OS does not recognize server clusters by default; you must configure it to do so. When
an ARP request is sent to a server cluster, either the active server or all the servers send a reply, depending on the cluster configuration. If
the active server sends a reply, the Dell switch learns the active server’s MAC address. If all servers reply, the switch registers only the last
received ARP reply and the switch learns one server’s actual MAC address; the virtual MAC address is never learned. Because the virtual
MAC address is never learned, traffic is forwarded to only one server rather than the entire cluster, and failover and balancing are not
preserved.
To preserve failover and balancing, the switch forwards the traffic destined for the server cluster to all member ports in the VLAN
connected to the cluster. To ensure that this happens, use the
ip vlan-flooding
command on the Dell switch when you configure the
Microsoft cluster. The server MAC address is given in the Ethernet frame header of the ARP reply, while the virtual MAC address
representing the cluster is given in the payload. Then, all the traffic destined for the cluster is flooded out of all member ports. Because all
the servers in the cluster receive traffic, failover and balancing are preserved.
Enable and Disable VLAN Flooding
• The older ARP entries are overwritten whenever newer NLB entries are learned.
• All ARP entries, learned after you enable VLAN flooding, are deleted when you disable VLAN flooding, and RP2 triggers an ARP
resolution. Disable VLAN flooding with the
no ip vlan-flooding
command.
• When you add a port to the VLAN, the port automatically receives traffic if you enabled VLAN flooding. Old ARP entries are not deleted
or updated.
• When you delete a member port, its ARP entries are also deleted from the content addressable memory (CAM).
• Port channels in the VLAN also receive traffic.
• There is no impact on the configuration from saving the configuration.
• If you enable VLAN flooding, it displays in the
show running-config
command output that displays the
ip vlan-flooding
CLI configuration. This is the only output where you see the VLAN flooding status (enabled or disabled).
Configuring a Switch for NLB
To enable a switch for Unicast NLB mode, perform the following steps:
472 Microsoft Network Load Balancing