Bellow is what I get on my attempt of pushing the rebase topic:

[yzaspits@yz-dell2 ovirt-engine]$ git push gerrit.ovirt.org:ovirt-engine HEAD:refs/for/master/ipv6
Counting objects: 1275, done.
Delta compression using up to 8 threads.
Compressing objects: 100% (515/515), done.
Writing objects: 100% (1275/1275), 164.53 KiB | 0 bytes/s, done.
Total 1275 (delta 540), reused 1060 (delta 341)
remote: Resolving deltas: 100% (540/540)
remote: Processing changes: updated: 15, refs: 16, done   
remote: error: internal error while processing changes
To gerrit.ovirt.org:ovirt-engine
 ! [remote rejected] HEAD -> refs/for/master/ipv6 (internal error)
error: failed to push some refs to 'gerrit.ovirt.org:ovirt-engine'

The command run took about 5-10 minutes, during which was very slow progress in the "updated" count. Fetching takes very long time too.

I tried pinging gerrit.ovirt.org but didn't find a problem in the network. Also ssh -T works relatively fast.