the answer is here:http://wiki.libvirt.org/page/Migration_fails_with_%22Unable_to_resolve_address%22_error

2012/12/6 zhijun liu <lzjun567@gmail.com>

2012/12/6 Gao Yongwei <itxx00@gmail.com>

2012/12/6 zhijun liu <lzjun567@gmail.com>

2012/12/6 Eric Blake <eblake@redhat.com>

On 12/05/2012 12:05 PM, zhijun liu wrote:
> hi,all
>
> when I try to migrate `vm0` from (192.168.1.102) to another
> host(192.168.1.200), the name `ubuntu1204` is 192.168.1.200's hostname.
>
> command is :
>
> `sudo virsh migrate --live vm0 qemu+tcp://192.168.1.200/system`
>
> the error is : unable to connect to server at 'ubuntu1204:49157':
> Connection refused.

Indeed, when using native migration, you have to open a rather large
range of ports that qemu might want to use.

http://wiki.libvirt.org/page/FAQ#What_setup_is_required_for_QEMU.2FKVM_migration.3F

>
> however,when I try to virsh connect to 192.168.1.200 by tcp is no problem.

http://libvirt.org/migration.html gives more details on how to do live
migration; in particular, you may want to try using --p2p to avoid
having to open any ports for qemu.

>
> I dont know what the port 49157?how to fix it?

Otherwise, figure out how to add open ports to your firewall; but as I'm
not an Ubuntu user, I can't really say how to do that on your system.

thanks, Blake. when I using --p2p ,the problem still exsit.
i think you could use ss command or netstat command when migrate begin,to check that which ports are opened,or which ports want to connect to, then check your firewall like iptables .

at the same time,another question is why the content of error " unable to connect to server at 'ubuntu1204:49157':" displayed hostname 'ubuntu1204' instead of ip '192.168.1.200'. beause I try to ping hostname `ubuntu1204` ,show `ping: unknown host ubuntu1204` ,only support ping `ip`.

if you doesnot have a nameserver,you could write the hostname and ip host /etc/hosts,and change the server's hostname .

when I operated in CentOS,the error like following:
error: Unable to resolve address '$hostname' service '49158': Name or service not known