Reference Guide

A Level 2 router becomes a neighbor with another Level 2 router regardless of the area address configured. However, if the
area addresses are different, the link between the Level 2 routers is only at Level 2.
Configuring Multi-Topology IS-IS (MT IS-IS)
To configure multi-topology IS-IS (MT IS-IS), use the following commands.
1. Enable multi-topology IS-IS for IPv6.
ROUTER ISIS AF IPV6 mode
multi-topology [transition]
Enter the keyword transition to allow an IS-IS IPv6 user to continue to use single-topology mode while upgrading to
multi-topology mode. After every router has been configured with the transition keyword, and all the routers are in MT
IS-IS IPv6 mode, you can remove the transition keyword on each router.
NOTE: When you do not enable transition mode, you do not have IPv6 connectivity between routers operating in single-
topology mode and routers operating in multi-topology mode.
2. Exclude this router from other routers SPF calculations.
ROUTER ISIS AF IPV6 mode
set-overload-bit
3. Set the minimum interval between SPF calculations.
ROUTER ISIS AF IPV6 mode
spf-interval [level-l | level-2 | interval] [initial_wait_interval
[second_wait_interval]]
Use this command for IPv6 route computation only when you enable multi-topology. If using single-topology mode, to apply
to both IPv4 and IPv6 route computations, use the spf-interval command in CONFIG ROUTER ISIS mode.
4. Implement a wide metric-style globally.
ROUTER ISIS AF IPV6 mode
isis ipv6 metric metric-value [level-1 | level-2 | level-1-2]
To configure wide or wide transition metric style, the cost can be between 0 and 16,777,215.
Configuring IS-IS Graceful Restart
To enable IS-IS graceful restart globally, use the following commands. Additionally, you can implement optional commands to
enable the graceful restart settings.
Enable graceful restart on ISIS processes.
ROUTER-ISIS mode
graceful-restart ietf
Configure the time during which the graceful restart attempt is prevented.
ROUTER-ISIS mode
graceful-restart interval minutes
The range is from 1 to 120 minutes.
The default is 5 minutes.
Enable the graceful restart maximum wait time before a restarting peer comes up.
ROUTER-ISIS mode
graceful-restart restart-wait seconds
When implementing this command, be sure to set the t3 timer to adjacency on the restarting router.
The range is from 1 to 120 minutes.
The default is 30 seconds.
Configure the time that the graceful restart timer T1 defines for a restarting router to use for each interface, as an interval
before regenerating Restart Request (an IIH with RR bit set in Restart TLV) after waiting for an acknowledgement.
ROUTER-ISIS mode
Intermediate System to Intermediate System
413