140
Preboot Execution Environment
The Preboot Execution Environment (PXE) allows a system to boot from an operating system image
over the network. By definition, PXE is invoked before an operating system is loaded, so there is no
opportunity for the BASP intermediate driver to load and enable a team. As a result, teaming is not
supported as a PXE client, though a physical adapter that participates in a team when the operating
system is loaded may be used as a PXE client. Whereas a teamed adapter cannot be used as a PXE
client, it can be used for a PXE server, which provides operating system images to PXE clients using
a combination of Dynamic Host Control Protocol (DHCP) and the Trivial File Transfer Protocol
(TFTP). Both of these protocols operate over IP and are supported by all teaming modes.
4.8
General Network Considerations
4.8.1 Teaming Across Switches
SLB teaming can be configured across switches. The switches, however, must be connected together.
Generic Trunking and Link Aggregation do not work across switches because each of these
implementations requires that all physical adapters in a team share the same Ethernet MAC address.
It is important to note that SLB can only detect the loss of link between the ports in the team and their
immediate link partner. SLB has no way of reacting to other hardware failures in the switches and
cannot detect loss of link on other ports.
4.8.2 Switch-Link Fault Tolerance
The diagrams below describe the operation of an SLB team in a switch fault tolerant configuration.
We show the mapping of the ping request and ping replies in an SLB team with two active members.
All servers (Blue, Gray and Red) have a continuous ping to each other. "• Teaming Across Switches
Without an Interswitch Link" (
J
pg.141) is a setup without the interconnect cable in place between
the two switches. "• Teaming Across Switches With Interconnect" (
J
pg.142) has the interconnect
cable in place, and "• Failover Event" (
J
pg.142) is an example of a failover event with the
Interconnect cable in place. These scenarios describe the behavior of teaming across the two switches
and the importance of the interconnect link.
The diagrams show the secondary team member sending the ICMP echo requests (arrow of a dotted
line), while the primary team member receives the respective ICMP echo replies (arrow of a double
line). This illustrates a key characteristic of the teaming software. The load balancing algorithms do
not synchronize how frames are load balanced when sent or received. In other words, frames for a
given conversation can go out and be received on different interfaces in the team. This is true for all
types of teaming supported by Broadcom. Therefore, an interconnect link must be provided between
the switches that connect to ports in the same team.
In the configuration without the interconnect, an ICMP Request from Blue to Gray goes out port
82:83 destined for Gray port 5E:CA, but the Top Switch has no way to send it there because it cannot
go along the 5E:C9 port on Gray. A similar scenario occurs when Gray attempts to ping Blue. An
ICMP Request goes out on 5E:C9 destined for Blue 82:82, but cannot get there. Top Switch does not
have an entry for 82:82 in its CAM table because there is no interconnect between the two switches.
Pings, however, flow between Red and Blue and between Red and Gray.
