How are IRO objects used for path calculation?

IRO object for path calculation

NSP supports the IRO object specification within a PCC request. NSP computes a CSPF path from the source to the IRO object, and another CSFP path from the IRO object to the destination. If the second CSPF path visits any of the nodes in first CSPF path, the path computation fails.

When used with a path profile policy that contains the bidirectional disjoint specification, a forward LSP and its matching reverse LSP must share the same IRO configuration. This means that the list of addresses in the IRO path must be the same, but their order reversed. This is because the disjoint algorithm is natively bidirectional strict. If the reverse LSP contained IROs that did not exist in the forward path, no path would be found, because it would no longer be bidirectional strict.

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