Broadcom Teaming Services: Broadcom NetXtreme II Network Adapter User Guide
file:///T|/htdocs/NETWORK/BroadCom/71921/NetXtremeII/en/teamsvcs.htm[9/26/2012 3:29:14 PM]
protocol stack responds to ARP Requests. In addition, each physical adapter in the team uses the same team MAC address
when transmitting frames. This is possible since the switch at the other end of the link is aware of the teaming mode and will
handle the use of a single MAC address by every port in the team. The forwarding table in the switch will reflect the trunk as a
single virtual port.
In this teaming mode, the intermediate driver controls load balancing and failover for outgoing traffic only, while incoming
traffic is controlled by the switch firmware and hardware. As is the case for Smart Load Balancing, the BASP intermediate
driver uses the IP/TCP/UDP source and destination addresses to load balance the transmit traffic from the server. Most
switches implement an XOR hashing of the source and destination MAC address.
NOTE: Generic Trunking is not supported on iSCSI offload adapters.
Link Aggregation (IEEE 802.3ad LACP)
Link Aggregation is similar to Generic Trunking except that it uses the Link Aggregation Control Protocol to negotiate the
ports that will make up the team. LACP must be enabled at both ends of the link for the team to be operational. If LACP is not
available at both ends of the link, 802.3ad provides a manual aggregation that only requires both ends of the link to be in a
link up state. Because manual aggregation provides for the activation of a member link without performing the LACP message
exchanges, it should not be considered as reliable and robust as an LACP negotiated link. LACP automatically determines
which member links can be aggregated and then aggregates them. It provides for the controlled addition and removal of
physical links for the link aggregation so that no frames are lost or duplicated. The removal of aggregate link members is
provided by the marker protocol that can be optionally enabled for Link Aggregation Control Protocol (LACP) enabled
aggregate links.
The Link Aggregation group advertises a single MAC address for all the ports in the trunk. The MAC address of the Aggregator
can be the MAC addresses of one of the MACs that make up the group. LACP and marker protocols use a multicast destination
address.
The Link Aggregation control function determines which links may be aggregated and then binds the ports to an Aggregator
function in the system and monitors conditions to determine if a change in the aggregation group is required. Link
aggregation combines the individual capacity of multiple links to form a high performance virtual link. The failure or
replacement of a link in an LACP trunk will not cause loss of connectivity. The traffic will simply be failed over to the
remaining links in the trunk.
SLB (Auto-Fallback Disable)
This type of team is identical to the Smart Load Balance and Failover type of team, with the following exception—when the
standby member is active, if a primary member comes back on line, the team continues using the standby member rather
than switching back to the primary member. This type of team is supported only for situations in which the network cable is
disconnected and reconnected to the network adapter. It is not supported for situations in which the adapter is
removed/installed through Device Manager or Hot-Plug PCI.
If any primary adapter assigned to a team is disabled, the team functions as a Smart Load Balancing and Failover type of
team in which auto-fallback occurs.
TOE Teaming
All four basic teaming modes support failover of traffic from a failed adapter to other working adapters. All four teaming
modes also support bidirectional load-balancing of TCP/IP traffic. A primary difference between the modes is that the SLB
modes use a Broadcom proprietary algorithm to control how both inbound and outbound traffic is balanced across the
network interfaces in the team. This has several advantages. First, with Generic Trunking or Link Aggregation modes, the
team of network adapters must be connected to a switch that is specifically configured to support that particular mode of
teaming. Since there is a dependency between the switch and the host team configuration when Generic Trunking or Link
Aggregation is used, it can often lead to configuration difficulties, because both ends must be configured correctly and be
synchronized. Second, with Generic Trunking or Link Aggregation modes, the switch decides how inbound traffic to the team
is balanced across the adapters, while BASP only controls the balancing of outbound traffic. This is problematic for TOE
environments, because in order for TOE to work, state information about a given TCP connection is stored in the hardware on
a given offloaded adapter, but it is not stored in the hardware on every member of the team. So teaming and TOE cannot co-
exist if the teaming software cannot steer incoming TCP/IP traffic to the adapter that contains and updates the state
information for a given TCP connection.
Because Broadcom's SLB modes can control how both outbound and inbound packets are balanced across the adapters, the
SLB modes are capable of ensuring that all offloaded TCP traffic for a given TCP connection goes in and out of a particular
adapter. This architectural feature allows the SLB modes to also support load-balancing on adapters that have TOE enabled,
since BASP is able to steer traffic on a particular TCP connection to the adapter hardware that contains offloaded state
