apt uses SRV records: $ dig +short -t SRV _http._tcp.ftp.us.debian.org 0 2 80 ftp-nyc.osuosl.org. 0 1 80 debian.gtisc.gatech.edu. 0 1 80 ftp-chi.osuosl.org. That's where you're getting the host name ftp-chi.osuosl.org from.