Administrator 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 router’s 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. Also, 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. This time is an
interval before regenerating Restart Request (an IIH with RR bit set in Restart TLV) after waiting for an acknowledgement.
ROUTER-ISIS mode
492
Intermediate System to Intermediate System