IBM PureFlex System and IBM Flex System Products and Technology

262 IBM PureFlex System and IBM Flex System Products and Technology

6.4.1 Redundant network topologies

The Enterprise Chassis can be connected to the enterprise network in several ways

(Figure 6-4).

Figure 6-4 IBM redundant paths

Topology 1 in Figure 6-4 has each switch module in Enterprise Chassis directly connected to

the one of the top of rack switches. The switch modules are connected through aggregation

links by using some of the external ports on the switch. The specific number of external ports

used for link aggregation depends on your redundancy requirements, performance

considerations, and real network environments. This topology is the simplest way to integrate

the Enterprise Chassis into an existing network, or to build a new one.

Topology 2 in Figure 6-4 has each switch module in the Enterprise Chassis with two direct

connections to a pair of top of rack switches. This topology is more advanced, and has a

higher level of redundancy. However, protocols such as Spanning Tree or Virtual Link

Aggregation Groups must be implemented. Otherwise, network loops and broadcast storms

might cause network failures.

6.4.2 Spanning Tree Protocol

Spanning Tree Protocol (STP) is a 802.1D standard protocol used in Layer 2 redundant

network topologies. When multiple paths exist between two points on a network, STP or one

of its enhanced variants can prevent broadcast loops. It can also ensure that the switch uses

the most efficient network path. STP can also enable automatic network reconfiguration in

case of failure. For example, top of rack switch 1 and 2, together with switch 1 in the

Compute node

NIC 2

NIC 1

Switch 1

TOR

Switch 1

TOR

Switch 2

Switch 2

Rest of

Network

Compute node

NIC 2

NIC 1Switch 1

TOR

Switch 1

TOR

Switch 2

Switch 2

Rest of

Network

Trunk

Topology 1

Topology 2

Chassis

Chassis