In regular SEP networking shown in Figure 1, a physical ring network can be configured with only one SEP segment in which only one interface can be blocked.
If an interface in the SEP segment in the complete state is blocked, all user package is transmitted only along the path where the primary edge interface resides. The path where the secondary edge interface resides is idle, wasting bandwidths.
Figure 1 Networking diagram for SEP
SEP multi-instance allows two SEP segments to be configured on one physical ring network. All devices, interface roles, and control VLANs in each SEP segment must be configured by conforming to basic SEP configurations principles. Each SEP segment has one blocked interface. Each blocked interface detects whether the physical ring network is complete. The blocked interfaces in the two SEP segments are independent of each other.
Each SEP segment needs to be configured with a protected instance and each protected instance represents a VLAN range. The topology calculated by a SEP segment is valid only for that SEP segment.
After different protected instances are configured for SEP segments and the mapping between protected instances and VLANs is set, a blocked interface is valid only for the VLANs protected by the SEP segment where the blocked interface resides. Data traffic of different VLANs can be transmitted along different paths. This implements traffic load balancing and link backup.
Figure 2 Networking diagram for SEP multi-instance
As shown in Figure 2, the SEP multi-instance ring network that consists of LSW1 to LSW4 has two SEP segments. P1 is the blocked interface in SEP segment 1, and P2 is the blocked interface in SEP segment 2.
Protected instance 1 is configured in SEP segment 1 to protect the data of VLAN 100 to VLAN 200. The data is transmitted along path LSW1->LSW2. As the blocked interface in SEP segment 2, P2 blocks only the data of VLAN 201 to VLAN 400.
Protected instance 2 is configured in SEP segment 2 to protect the data of VLAN 201 to VLAN 400. The data is transmitted along path LSW3->LSW4. As the blocked interface in SEP segment 1, P1 blocks only the data of VLAN 100 to VLAN 200.
In the case of a node or a link failure, each SEP segment calculates its own topology independently, and the nodes in each SEP segment update their LSA databases.
As shown in Figure 3, a fault occurs on the link between LSW3 and LSW4. The link fault does not affect the transmission path for the data of VLAN 100 to VLAN 200 in SEP segment 1, but blocks the transmission path for the data of VLAN 201 to VLAN 400 in SEP segment 2.
Figure 3 Networking diagram for a fault in a link on a SEP muti-instance network
After the link between LSW3 and LSW4 becomes faulty, LSW3 starts to send LSAs to instruct the other devices in SEP segment 2 to refresh their LSA databases, and the blocked interface enters the forwarding state. After the topology of SEP segment 2 is recalculated, the data of VLAN 201 to VLAN 400 is transmitted along path LSW3->LSW1->LSW2.
After the link between LSW3 and LSW4 recovers, the devices in SEP segment 2 performs delayed preemption. After the preemption delay expires, P1 becomes the blocked interface again, and sends LSAs to instruct the other devices in SEP segment 2 to refresh their LSA databases. After the topology of SEP segment 2 is recalculated, the data of VLAN 201 to VLAN 400 is transmitted along path LSW3->LSW4.
