Interesting, those IP addresses are under a different AS and under a different organization, that of National Library of Medicine. They don't seem to use the IT infrastructure of nih.gov.
Yeaaaahhhh...NLM is/was a special beast inside NIH.
At the time I was there they had a budget to die for, and Pubmed was in the top 300 websites in the world (both are probably still true). NLM pushed so much traffic because of Pubmed that they had their own internet connection to avoid DoS'ing the commodity desktop traffic of the rest of the NIH.
PubMed is self hosted in a datacenter located within NLM on the NIH campus.
They also have their own fiber connections as you mentioned.
There is also a legit storage vault located within the building that houses non digital records. We were told that there were medical records going back thousands of years kept there; and possibly as far back as the Egyptian era.
