This is deb.debian.org. This service provides mirrors for the following Debian archive repositories: /debian/ /debian-debug/ /debian-ports/ /debian-security/ /debian-security-debug/ The server deb.debian.org does not have packages itself, but the name has SRV records in DNS that lets apt in stretch and later find places. To use it with a sufficiently recent apt, you for instance can put deb http:/