dbanck's questions

I'm using a IPv4 + IPv6 on a server (#1).

Sometimes the IPv4 address is mapped to another server (#2), so #1 isn't accessible via IPv4, but remains accessible via IPv6.

In this case IPv6 dns lookups won't work.

$ ping6 mirror.ipv6.hetzner.de
unknown host

If I disable the IPv4 address everything works fine.

$ ping6 mirror.ipv6.hetzner.de
PING mirror.ipv6.hetzner.de(2a01:4f8:0:a101::1:1) 56 data bytes
64 bytes from 2a01:4f8:0:a101::1:1: icmp_seq=1 ttl=60 time=0.469 ms

How is this possible? The IPv6 network should serve as a fallback if the IPv4 address is mapped to another server. But if I can't resolve any hostnames, i can't really work with it.

Are there any possibilities to make IPv6 dns work nevertheless IPv4 is available or not?

Edit:

/etc/resolv.conf

$ cat /etc/resolv.conf 
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 213.133.99.99
nameserver 213.133.100.100
nameserver 213.133.98.98
nameserver 2a01:4f8:0:a0a1::add:1010
nameserver 2a01:4f8:0:a102::add:9999
nameserver 2a01:4f8:0:a111::add:9898

Routing:

$ route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         5.9.61.167      0.0.0.0         UG    100    0        0 eth0
5.9.61.167      0.0.0.0         255.255.255.255 UH    0      0        0 eth0

$ route -6
Kernel IPv6 routing table
Destination                    Next Hop                   Flag Met Ref Use If
2a01:4f8:162:7ffe:1::2/128     ::                         U    1024 0     1 eth0
2a01:4f8:162:7ffe:6::/80       ::                         U    256 0     0 eth0
fe80::/64                      ::                         U    256 0     0 eth0
::/0                           2a01:4f8:162:7ffe:1::2     UG   1024 0     0 eth0
::/0                           ::                         !n   -1  1     6 lo
::1/128                        ::                         Un   0   1     5 lo
2a01:4f8:162:7ffe:6::2/128     ::                         Un   0   1   190 lo
fe80::5054:ff:fe3d:5f4c/128    ::                         Un   0   1     0 lo
ff00::/8                       ::                         U    256 0     0 eth0
::/0                           ::                         !n   -1  1     6 lo

I'm using KVM with qemu/libvirtd for virtualization in my local network.

Now I'm working on a script which should simplify the cloning and downloading process of virtual machines. For this I need to know the IP addresses of those. For example, get the ip of the fresh created/cloned vm.

The setup is the following:

• a hypervisor with one bridge which is used by all virtual machines
• all vms get an ip from an external dhcp server
• an external dhcp server (on a fritz.box) (which could be replaced by one running on the hypervisor)

Some of the following approaches might be possible:

• I can get the mac address from the qemu-config files and use it to look up the associated ip address inside the dhcp server
• Doing a broadcast ping won't return all active vms in the network, but one could use some weird bash loop to ping all 254 ips. (will create some big overhead; I don't like it)
• After this use arp to grep an ip according to the mac address from the config file

Are there some more elegant ways to achieve this?

As you might know that it's not as easy to generate entropy on a virtual machine as on a "normal" pc. Generating a gpg-key on a virtual machine can take a while, even with the correct tools.

There are plenty more crypto functions out there which aren't so entropy aware as gpg is.

So can one say that cryptography is less secure on a virtual machine?