This task explains how to configure multi topology IS-IS in IPv6. For these optional configuration steps it is assumed that IS-IS for IPv6 is already configured as described in the previous section. The commands described below may then be entered in the configuration context of the corresponding ISIS routing process.
When multi topology IS-IS for IPv6 is configured, the transition keyword allows a user who is working with the single topology SPF mode of IS-IS IPv6 to continue to work while upgrading to multi topology IS-IS. After every router is configured with the transition keyword, users can remove the transition keyword on each router. When transition mode is not enabled, IPv6 connectivity between routers operating in single topology mode and routers operating in multi topology mode is not possible.
You can continue to use the existing IPv6 topology while upgrading to multi topology IS-IS. The optional isis ipv6 metric command allows you to differentiate between link costs for IPv6 and IPv4 traffic when operating in multi topology mode.
Command syntax to enable multi topology IS-IS:
The following command configures a router running IS-IS to generate and accept only new style TLVs:
Router(config-router)# metric-style wide [transition] \\
[level-1 | level-2 | level-1-2]
Now, one enters IPv6 address family configuration mode.
Router(config-router)# address-family ipv6 [unicast]
The unicast keyword specifies the IPv6 unicast address family which is the default in this case anyway.
Within the IPv6 address family multi topology IS-IS for IPv6 can be enabled with the following command:
Router(config-router-af)# multi-topology [transition]
The optional transition keyword allows an IS-IS IPv6 user to continue to use single topology mode while upgrading to multi topology mode (s.a.).
Examples
In the following example a previously configured (single topology) IS-IS session “area2” is switched to multi topology IS-IS.
