3.8.e Describe optimization features

3.8.e [i] Metrics, wide metric

Cisco IOS Software allows for wide metrics with the support of a 24-bit metric field. Using the new metric style, link metrics now have a maximum value of 16777215 (2 24-1) with a total path metric of 4261412864 (254 x 2 24). Deploying IS-IS in the IP network with wide metrics is recommended to enable finer granularity and to support future applications such as Traffic Engineering.

Running different metric styles within one network poses a serious problem: Link-state protocols calculate loop-free routes because all routers (within one area) calculate their routing table based on the same link- state database. This principle is violated if some routers look at old-style (narrow), and some at new-style (wider) TLVs. However, if the same interface cost is used for both the old- and new-style metrics, then the SPF will compute a loop-free topology.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 4317-4318).  . Kindle Edition.