Dell MXL 10/40GbE Graceful Restart

• MT ID #5: Reserved for IPv6 in-band management purposes.

All routers in the area or domain must use the same type of IPv6 support, either single-topology or multi-

topology. A router operating in multi-topology mode does not recognize the ability of the single-

topology mode router to support IPv6 traffic, which leads to holes in the IPv6 topology.

While in Transition mode, both types of TLVs (single-topology and multi-topology) are sent in LSPs for all

configured IPv6 addresses, but the router continues to operate in single-topology mode (that is, the

topological restrictions of the single-topology mode remain in effect). Transition mode stops after all

routers in the area or domain have been upgraded to support multi-topology IPv6. After all routers in the

area or domain are operating in multi-topology IPv6 mode, the topological restrictions of single-

topology mode are no longer in effect.

MT IS-IS is supported on physical Ethernet interfaces, physical synchronous optical network technologies

(SONET) interfaces, port-channel interfaces (static and dynamic using LACP), and virtual local area

network (VLAN) interfaces.

Adjacencies on point-to-point interfaces are formed as usual, where IS-IS routers do not implement MT

extensions.

If a local router does not participate in certain MTs, it does not advertise those MT IDs in its IS-IS hellos

(IIHs) and so does 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 does not form

an adjacency if both routers do not have at least one common MT over the interface.

Graceful Restart

Graceful Restart is supported on MXL platforms for both Helper and Restart modes.

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 route

processor module (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

Intermediate System to Intermediate System 483