Hello,

in the core-updates branch, tarballs are not downloaded automatically any 
more. Here is the result of "guix-build hello" (which tries to rebuild 
everything, as expected):

...
starting download of `/nix/store/c09pc1yvdai4ylb5i7x242aj66dy3f07-
glibc-2.17.tar.xz' from 
`http://ftpmirror.gnu.org/glibc/glibc-2.17.tar.xz'...
ERROR: In procedure getaddrinfo: Name or service not known
starting download of `/nix/store/c09pc1yvdai4ylb5i7x242aj66dy3f07-
glibc-2.17.tar.xz' from `ftp://ftp.cs.tu-
berlin.de/pub/gnu/glibc/glibc-2.17.tar.xz'...
failed to resolve `ftp.cs.tu-berlin.de': Name or service not known
ERROR: In procedure struct_vtable: Wrong type argument in position 1 
(expecting pair): #f
starting download of `/nix/store/c09pc1yvdai4ylb5i7x242aj66dy3f07-
glibc-2.17.tar.xz' from 
`ftp://ftp.chg.ru/pub/gnu/glibc/glibc-2.17.tar.xz'...
failed to resolve `ftp.chg.ru': Name or service not known
ERROR: In procedure struct_vtable: Wrong type argument in position 1 
(expecting pair): #f
starting download of `/nix/store/c09pc1yvdai4ylb5i7x242aj66dy3f07-
glibc-2.17.tar.xz' from 
`ftp://ftp.funet.fi/pub/mirrors/ftp.gnu.org/gnu/glibc/glibc-2.17.tar.xz'...
failed to resolve `ftp.funet.fi': Name or service not known
ERROR: In procedure struct_vtable: Wrong type argument in position 1 
(expecting pair): #f
starting download of `/nix/store/c09pc1yvdai4ylb5i7x242aj66dy3f07-
glibc-2.17.tar.xz' from 
`http://ftp.gnu.org/pub/gnu/glibc/glibc-2.17.tar.xz'...
ERROR: In procedure getaddrinfo: Name or service not known
failed to download "/nix/store/c09pc1yvdai4ylb5i7x242aj66dy3f07-
glibc-2.17.tar.xz" from "mirror://gnu/glibc/glibc-2.17.tar.xz"
...

On the other hand,
   guix-download http://ftpmirror.gnu.org/glibc/glibc-2.17.tar.xz
succeeds.

Andreas