Debian mirrors backed by Fastly CDN

This is deb.debian.org. This service provides mirrors for the following Debian archive repositories:

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://deb.debian.org/debian unstable main
deb http://deb.debian.org/debian-debug unstable-debug main
deb http://deb.debian.org/debian-ports unstable main
in your sources.list.

As of July 2022 the SRV record is 

_http._tcp.deb.debian.org.    IN      SRV     10 1 80 prod.debian.map.fastly.net.
If you hit the server behind deb.debian.org directly, either because you use an older apt or because you use a HTTP proxy that does not support SRV records, your requests will get HTTP redirected to one of the CDN instances. If you want to avoid the redirects, you can pick one instance directly. For instance, this also works in your sources.list: 
deb http://cdn-fastly.deb.debian.org/debian stable main
deb http://cdn-fastly.deb.debian.org/debian-security stable-security main
deb http://cdn-fastly.deb.debian.org/debian-security-debug stable-security-debug main
This service is sponsored by Fastly.

DSA