Dell Force10 S4820T S4820T Configuration Guide - Page 516

www.dell.com | support.dell.com Interface support MT IS-IS is supported on physical Ethernet interfaces, physical Sonet interfaces, port-channel interfaces (static & dynamic using LACP), and VLAN interfaces. Adjacencies Adjacencies on point-to-point interfaces are formed as usual, where IS-IS routers do not implement Multi-Topology (MT) extensions. If a local router does not participate in certain MTs, it will not advertise those MT IDs in its IIHs and so will not include that neighbor within its LSPs. If an MT ID is not detected in the remote side's IIHs, the local router does not include that neighbor within its LSPs. The local router will not form an adjacency if both routers don't have at least one common MT over the interface. Graceful Restart e Graceful Restart is supported on the and modes. and S4820T platforms for both Helper and Restart Graceful Restart is a protocol-based mechanism that preserves the forwarding table of the restarting router and its neighbors for a specified period to minimize the loss of packets. A graceful-restart router does not immediately assume that a neighbor is permanently down and so does not trigger a topology change. Normally, when an IS-IS router is restarted, temporary disruption of routing occurs due to events in both the restarting router and the neighbors of the restarting router. 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. IS-IS Graceful Restart recognizes the fact that in a modern router, the control plane and data plane are functionally separate. Restarting the control plane functionality (such as the failover of the active RPM to the backup in a redundant configuration) should not necessarily interrupt data packet forwarding. 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 can continue uninterrupted while the control plane IS-IS process comes back to full functionality and rebuilds its routing tables. A new TLV (the Restart TLV) is introduced in the IIH PDUs, indicating that the router supports Graceful Restart. Timers Three timers are used to support IS-IS Graceful Restart functionality. Once Graceful Restart is enabled, these timers manage the Graceful Restart process. 516 | Intermediate System to Intermediate System