Multi-Chassis APS functionality extends the protection offered by SC-APS to include protection against nodal (7750 SR) failure by configuring the working circuit of an APS group on one 7750 SR node while configuring the protect circuit of the same APS group on a different 7750 SR node.
These two nodes connect to each other with an IP link to establish an MC-APS signaling path between the two 7750 SRs. Note that the working circuit and the protect circuit must have compatible configurations (such as the same speed, framing, and port-type). The relevant APS groups in both the working and protection routers must have same group ID, but they can have different names (for example, group port descriptions). Although the working and protection routers can be different platforms (7750 SR-7 and a 7750 SR-c12), switchover performance may be impacted so it is recommended to avoid a mix of platforms in the same MC-APS group where possible. The configuration consistency between the working circuit/router and the protection circuit/router is not enforced by the 7750 SR. Service or network-specific configuration data is not signaled nor synchronized between the two service routers.
Signaling is provided using the direct connection between the two service routers. A heartbeat protocol can be used to add robustness to the interaction between the two routers. Signaling functionality includes support for:
APS group matches between service routers.
Verification that one side is configured as a working circuit and the other side is configured as the protect circuit. In case of a mismatch, a trap (incompatible neighbor) is generated.
Change in working circuit status is sent from the working router to keep the protect router in sync.
Protect router, based on K1/K2 byte data, member circuit status, and external request, selects the active circuit, and informs the working router to activate or de-activate the working circuit.
Note that external requests like lockout, force, and manual switches are allowed only on the APS group having the protection circuit.
The Figure 1 shows a Multi-Chassis APS group being used to protect against link, port, MDA, IOM or node failure.
