Avaya 8800 Planning And Engineering, Network Design page 98

Layer 2 loop prevention
In the following figure, all three devices are members of STG1 and VLAN1. Link Y is in a blocking
state to prevent a loop, and links X and Z are in a forwarding state. With this configuration,
congestion on link X is possible because it is the only link that forwards traffic between
EthernetSwitchA and ERS8600C.
Figure 30: One STG between two Layer 3 devices and one Layer 2 device
To provide load sharing over links X and Y, create a configuration with multiple STGs that are
transparent to the Layer 2 device and that divide the traffic over different VLANs. To ensure that the
multiple STGs are transparent to the Layer 2 switch, the BPDUs for the two new STGs (STG2 and
STG3) must be treated by the Ethernet Switch as regular traffic, not as BPDUs.
In the configuration in
page 99, the BPDUs generated by the two STGs (STG2 and STG3) are forwarded by the Ethernet
Switch 8100. To create this configuration, you must configure STGs on the two Ethernet Routing
Switch 8800/8600s, assign specific MAC addresses to the BPDUs created by the two new STGs,
create VLANs 4002 and 4003 on the Layer 2 device, and create two new VLANs (VLAN 2 and
VLAN 3) on all three devices.
June 2016
Figure 31: Alternative configuration for STG and Layer 2 devices
Planning and Engineering — Network Design
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