Ronald> is there a number that this means, i.e. is ifconfig saying
Ronald> "I don't know this number so it is UNSPEC" or is it a
Ronald> number that means "NaN"?
The former. IPoIB reports its (IANA-assigned) link type of 32.
Depending on how new a version you have, "ip addr" will either show
"link/[32]" or "link/infiniband".
- R.