Hello Chase
In the context of the IS-IS protocol, the maximum values for composite metrics can be a source of confusion due to the specifications and implementations. Here are some aspects of this topic that will help to clarify:
What are the maximum composite metrics in IS-IS:
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Default IS-IS Metrics:
- IS-IS uses a default metric of 10 for links, and the maximum default metric value for a single link is 63.
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Wide Metrics:
- With the introduction of “wide metrics” to accommodate larger networks and provide more granular control over path selection, the maximum metric for a single link is extended to 16,777,215 (2^24-1).
- However, composite metrics for calculating the path can differ. The composite metric is essentially the sum of individual link metrics along the path.
Now the Cisco ENSLD 2.0 mentions the maximum composite values as 1024 and 64. However, this might be based on Cisco’s specific implementation or configuration context.
According to most sources, the values of 1023 and 63 are traditionally seen in older or default configurations without wide metric extensions. The 1024 and 64 values are likely referencing specific configurations or extensions, possibly considering a limit imposed by specific hardware or software versions.
Looking at the official RFC 1195 on page 17 it seems to alude to a maximum of 63. You have to remember that some vendors may not adhere strictly to the rules in the RFC and may adjust them as needed.
So there’s no official answer, I guess it really depends upon the implementation that you are using. If you’re using Cisco devices, I would trust the Cisco documentation.
I hope this has been helpful!
Laz