It is most likey firewall on CentOS. On my CentOS 7 client machine I have these ports open for Urbackup
-A IN_public_allow -p tcp -m tcp --dport 35621 -m conntrack --ctstate NEW -j ACCEPT
-A IN_public_allow -p udp -m udp --dport 35622 -m conntrack --ctstate NEW -j ACCEPT
-A IN_public_allow -p tcp -m tcp --dport 35623 -m conntrack --ctstate NEW -j ACCEPT
HTH