Migrating IS-IS from Narrow to Wide Metrics
As discussed in Chapter 3, IS-IS needs wide metrics enabled in order for MPLS TE to work. However, if you're running IS-IS already, chances are you're not running with wide metrics enabled. You might also have some devices in the network that don't understand wide metrics at all. The tricky bit in migrating from narrow to wide metric support is that you need to do so with as little service disruption as possible. If you just go to some routers and turn on metric-style wide, routers that don't understand wide-style metrics will not understand the IS-IS advertisements from the wide-style routers, and your network will break. So the goal here is to enable wide metrics with as little service disruption ...
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