DELL S6000-ON User Manual

For packets that have existing FIB/content addressable memory (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. After you enable graceful restart, 
these timers manage the graceful restart process.

There are three times, T1, T2, and T3.

• The T1 timer specifies the wait time before unacknowledged restart requests are generated. This is the 

interval before the system sends a Restart Request (an IIH with the RR bit set in Restart TLV) until the 

complete sequence number PDU (CSNP) is received from the helping router. You can set the duration 

to a specific amount of time (seconds) or a number of attempts.

• The T2 timer is the maximum time that the system waits for LSP database synchronization. This timer 

applies to the database type (level-1, level-2, or both).

• The T3 timer sets the overall wait time after which the router determines that it has failed to achieve 

database synchronization (by setting the overload bit in its own LSP). You can base this timer on 

adjacency settings with the value derived from adjacent routers that are engaged in graceful restart 

recovery (the minimum of all the Remaining Time values advertised by the neighbors) or by setting a 

specific amount of time manually.

Implementation Information

IS-IS implementation supports one instance of IS-IS and six areas.

You can configure the system as a Level 1 router, a Level 2 router, or a Level 1-2 router. For IPv6, the IPv4 
implementation has been expanded to include two new type, length, values (TLVs) in the PDU that carry 
information required for IPv6 routing. The new TLVs are IPv6 Reachability and IPv6 Interface Address. 
Also, a new IPv6 protocol identifier has also been included in the supported TLVs. The new TLVs use the 
extended metrics and up/down bit semantics.
Multi-topology IS-IS adds TLVs:

• MT TLV — contains one or more Multi-Topology IDs in which the router participates. This TLV is 

included in IIH and the first fragment of an LSP.

• MT Intermediate Systems TLV — appears for every topology a node supports. An MT ID is added to 

the extended IS reachability TLV type 22.

• MT Reachable IPv4 Prefixes TLV — appears for each IPv4 an IS announces for a given MT ID. Its 

structure is aligned with the extended IS Reachability TLV Type 236 and it adds an MT ID.

• MT Reachable IPv6 Prefixes TLV — appears for each IPv6 an IS announces for a given MT ID. Its 

structure is aligned with the extended IS Reachability TLV Type 236 and add an MT ID.

By default, Dell Networking OS supports dynamic host name exchange to assist with troubleshooting and 
configuration. By assigning a name to an IS-IS NET address, you can track IS-IS information on that 
address easier. Dell Networking OS does not support ISO CLNS routing; however, the ISO NET format is 
supported for addressing.

To support IPv6, the Dell Networking implementation of IS-IS performs the following tasks:

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Intermediate System to Intermediate System