Ypcat doesn't work on the netgroup table on a NIS+ server, why?

Yes, that is a known problem. The only operations allowed from
a NIS client side on the netgroup table are the ypmatches, but
not ypcat (i.e. no support for yp_first(), yp_next() or
yp_all() calls). The netgroup table is kind of unique in
this. The reason for this is that the netgroup table format
changed quite significantly in NIS+ and the NIS+ server would
take a big performance hit in converting the netgroups table to
YP (key-value) format.

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