Broadcom NetXtreme BCM57 Series, User Manual

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Broadcom Gigabit Ethernet Teaming Services NetXtreme User Guide
Broadcom
®
April 2017 • 2CS57XX-CDUM514-R Page 106
Smart Load Balancing and Failover
The Smart Load Balancing™ and Failover type of team provides both load balancing and failover when
configured for load balancing, and only failover when configured for fault tolerance. This type of team works with
any Ethernet switch and requires no trunking configuration on the switch. The team advertises multiple MAC
addresses and one or more IP addresses (when using secondary IP addresses). The team MAC address is
selected from the list of load balance members. When the system receives an ARP request, the software-
networking stack will always send an ARP Reply with the team MAC address. To begin the load balancing
process, the teaming driver will modify this ARP Reply by changing the source MAC address to match one of
the physical adapters.
Smart Load Balancing enables both transmit and receive load balancing based on the Layer 3/Layer 4 IP
address and TCP/UDP port number. In other words, the load balancing is not done at a byte or frame level but
on a TCP/UDP session basis. This methodology is required to maintain in-order delivery of frames that belong
to the same socket conversation. Load balancing is supported on 2 to 8 ports. These ports can include any
combination of add-in adapters and LAN on Motherboard (LOM) devices. Transmit load balancing is achieved
by creating a hashing table using the source and destination IP addresses and TCP/UDP port numbers.The
same combination of source and destination IP addresses and TCP/UDP port numbers will generally yield the
same hash index and therefore point to the same port in the team. When a port is selected to carry all the frames
of a given socket, the unique MAC address of the physical adapter is included in the frame, and not the team
MAC address. This is required to comply with the IEEE 802.3 standard. If two adapters transmit using the same
MAC address, then a duplicate MAC address situation would occur that the switch could not handle.
Receive load balancing is achieved through an intermediate driver by sending gratuitous ARPs on a client-by-
client basis using the unicast address of each client as the destination address of the ARP request (also known
as a directed ARP). This is considered client load balancing and not traffic load balancing. When the
intermediate driver detects a significant load imbalance between the physical adapters in an SLB team, it will
generate G-ARPs in an effort to redistribute incoming frames. The intermediate driver (BASP) does not answer
ARP requests; only the software protocol stack provides the required ARP Reply. It is important to understand
that receive load balancing is a function of the number of clients that are connecting to the system through the
team interface.
SLB receive load balancing attempts to load balance incoming traffic for client machines across physical ports
in the team. It uses a modified gratuitous ARP to advertise a different MAC address for the team IP Address in
the sender physical and protocol address. This G-ARP is unicast with the MAC and IP Address of a client
machine in the target physical and protocol address respectively. This causes the target client to update its ARP
cache with a new MAC address map to the team IP address. G-ARPs are not broadcast because this would
cause all clients to send their traffic to the same port. As a result, the benefits achieved through client load
balancing would be eliminated, and could cause out-of-order frame delivery. This receive load balancing
scheme works as long as all clients and the teamed system are on the same subnet or broadcast domain.
Generic Trunking
(FEC/GEC)/802.3ad-
Draft Static
Table 9: Available Teaming Types
Teaming Type
Switch-Dependent
(Switch must
support specific
type of team)
Link Aggregation
Control Protocol
support is required
on the switch Load Balancing Failover