It seems, that you are using your internal RH links in public gitlab repo, well...
$ uname -a
Linux localhost.localdomain 5.11.14-200.fc33.x86_64 #1 SMP Wed Apr 14 15:25:53 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
$ centpkg clone --anonymous -b c9s gcc
Cloning into 'gcc'...
warning: redirecting to https://gitlab.com/redhat/centos-stream/rpms/gcc.git/
remote: Enumerating objects: 181, done.
remote: Counting objects: 100% (181/181), done.
remote: Compressing objects: 100% (94/94), done.
remote: Total 181 (delta 96), reused 155 (delta 81), pack-reused 0
Receiving objects: 100% (181/181), 127.24 KiB | 259.00 KiB/s, done.
Resolving deltas: 100% (96/96), done.
$ cd gcc
$ centpkg sources
Downloading gcc-11.0.1-20210324.tar.xz
Could not execute sources: (6, 'Could not resolve host: sources.stream.rdu2.redhat.com')
 
26.04.2021, 21:32, "Brian Stinson" <bstinson@redhat.com>:


- Pull package sources from gitlab.com
    - `centpkg clone -b c9s <pkgname>` gives you a dist-git checkout from gitlab
    - `centpkg sources` from your checkout pulls source tarballs from
the lookaside cache