Dell Force10 E600i FTOS Version 8.4.1.5 Configuration Guide for ExaScale - Page 666

www.dell.com | support.dell.com FTOS supports Stub areas, Totally Stub (No Summary) and Not So Stubby Areas (NSSAs) and supports the following LSAs, as discussed earlier in this document. • Router (type 1) • Network (type 2) • Network Summary (type 3) • AS Boundary (type 4) • AS External (type 5) • NSSA External (type 7) • Opaque Link-local (type 9) Graceful Restart c e s Graceful Restart supported on and platforms for both Helper and Restart modes. When a router goes down without a Graceful Restart, there is a potential to lose access to parts of the network due to the necessity of network topology changes. Additionally, LSA flooding and reconvergence can cause substantial delays. It is, therefor, desirable that the network maintain a stable topology if it is possible for data flow to continue uninterrupted. OSPF Graceful Restart recognizes the fact that in a modern router, the control plane and data plane functionality are separate, restarting the control plane functionality (such as the failover of the active RPM to the backup in a redundant configuration), does not necessarily have to interrupt the forwarding of data packets. This behavior is supported because the forwarding tables previously computed by an active RPM have been downloaded into the Forwarding Information Base on the line cards (the data plane), and are still resident. For packets that have existing FIB/CAM entries, forwarding between ingress and egress ports/VLANs etc., can continue uninterrupted while the control plane OSPF process comes back to full functionality and rebuilds its routing tables. The grace period is the time period that a router defines for other adjacent routers to wait for it to return to full control plane functionality, and which it advertises to its neighbors. When an outage occurs, the neighbors will wait for this time period before flooding LSAs and beginning reconvergence. When a router is attempting to restart gracefully, it will originate Type 9 link local opaque grace-LSAs that notify its helper neighbors that the restart process is beginning. During this period, the helper neighbor routers continue to announce the restarting router as fully adjacent, as long as the network topology remains unchanged. When the restarting router completes its restart, it flushes the grace-LSAs, thereby notifying its neighbors that the restart is complete. This should happen before the grace period expires. Fast Convergence (OSPFv2, IPv4 only) Fast Convergence allows you to define the speeds at which LSAs are originated and accepted, and reduce OSPFv2 end-to-end convergence time. FTOS enables you to accept and originate LSAa as soon as they are available to speed up route information propagation. Note that the faster the convergence, the more frequent the route calculations and updates. This will impact CPU utilization and may impact adjacency stability in larger topologies. 666 | Open Shortest Path First (OSPFv2 and OSPFv3)