Design Reference

SLPP example scenarios
The following examples illustrate some situations where layer 2 loops can occur and how SLPP
prevents loops in those cases.
Scenario 1: VSP 4000 as an edge router
Scenario 1 demonstrates a triangular setup with ERS 8800 switches as IST peers, and VSP
4000 on the edge. From VSP 4000, there are four links that are part of the same MLT, with
SLPP enabled on the VSP 4000 ports. Because the MLT ports are misconfigured, loops can
occur. For example, port 1/1 on VSP 4000 can be part of the MLT, but on the ERS port, 2/1 is
not part of the MLT, although they are on the same VLAN.
Figure 9: VSP 4000 as an edge router
SLPP PDUs are generated by VSP 4000. If there is a loop, then the SLPP PDUs return to port
1/1. After the threshold value is reached, SLPP brings the ports down.
Scenario 2: VSP 4000 as an edge router but with an additional link to the ERS
8800
Scenario 2 is similar to scenario 1 except that there is an additional link from ERS 8800 to VSP
4000 that is not part of MLT 1. The additional link is a member of the SLPP-enabled VLAN,
and does not have to be directly connected from ERS 8800 to VSP 4000, but can be connected
from other DUTs interconnected to the ERS 8800 and VSP 4000.
Layer 2 loop prevention
46 Network Design Reference for Avaya VSP 4000 February 2014
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