Recommended Topology for Campus Fabric (SPX) ISSU

ISSU provides the ability to upgrade Campus Fabric (SPX) systems with minimal traffic loss.

Multi-PE unit LAGs are not supported in an SPX system, which means that traffic through a PE being upgraded is affected by the upgrade. ISSU reduces the network impact of an upgrade only if redundant uplink and downlink connections are available from multiple CB stack units.

Note: Because traditional LAGs are not supported on Port Extender (PE) units in an SPX system, dual connectivity (through two different PE units) is recommended for every PE chain or ring.

The following figure illustrates a typical topology where ISSU can be used effectively to upgrade an SPX system.

Recommended Topology for SPX ISSU

In the figure, redundant links connect different CB units in the SPX system to the uplink network. As each node is upgraded, it undergoes a hardware reset, which resets the packet processor and disrupts traffic flowing through the node. The redundant links allow traffic to flow through other units, minimizing the impact of each unit upgrade.

Parent topic: In-Service Software Upgrade