ISIS Max Metric – Understanding and Configuration Guide

is-is

I need to confirm the below as i don't have access to a lab.

I have 4 XR boxes connected linearly as shown.Router A is advertsing PC subnet in isis.
My understanding:
So when the subnet of PC A reaches the Router D, the overall metric
should be as

Cost of PC A to Router A link + 16777214(A-B link cost) + 16777214(B-C link cost) +16777214 (C-D link cost)
But the max metric in isis is 16777214, so will the final route get installed or not? If so, with what metric?

With what metric will Router D learn the subnet of PC connected to Router A?

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Best Answer

I just labbed it in VIRL. For the PC subnet, I get a metric of 50331642 on Router D:

Routing entry for 10.0.0.4/30
  Known via "isis 1", distance 115, metric 50331642, type level-2
  Installed Feb 28 17:46:19.166 for 00:00:07
  Routing Descriptor Blocks
    10.0.0.17, from 192.168.0.2, via GigabitEthernet0/0/0/0
      Route metric is 50331642
  No advertising protos.

Note that I had to manually set the IS-IS link metric to 16777214 on all applicable interfaces under the ISIS config. Otherwise it defaults to a link metric of 10 for a total metric of 30 on Router D.

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