The default metric value to announce this summary address with in Level
1 or 2 LSPs generated by this system. A Metric value of 0 indicates to
use the lowest metric value amongst the routes being summarized. When
advertising a metric value into a narrow domain (usdIsisSysL1MetricStyle
or usdIsisSysL2MetricStyle is set to usdIsisMetricStyleNarrow) the value
will be truncated to 63.