The value of vRtrMplsS2lSubLspMBBFailNodeAddr indicates the IP address
of the node in the S2L sub LSP at which the in-progress MBB failed. A
value of 'unknown' for vRtrMplsS2lSubLspMBBFailNodeType and empty
string for vRtrMplsS2lSubLspMBBFailNodeAddr indicates that no failure
has occurred.