Centos – IPv6 routing under KVM virtualization

centosipv6kvm-virtualization

I'm having trouble configuring IPv6 routing under KVM virtualization, and I need your help!

On the host machine. It uses bridge (named br0) to give its guest
machines Internet access.

On the guest machines running on the host, the IPv6 gateway is set as the IPv6 address of the host.

The problem is: on the virtual machine, "ping6 ipv6.google.com" gives:

ping6 ipv6.google.com
PING ipv6.google.com(nuq04s29-in-x0e.1e100.net) 56 data bytes
From [hostname] icmp_seq=3D1 Destination unreachable: Address unreachable

It seems that it can resolve the address but cannot reach the gateway.

"ip neigh show" gives the following output:

ip -6 neigh show
fe80::212:f2ff:fe9a:1700 dev ens3  FAILED
[IPv6 address of host machine] dev ens3  FAILED

While on the host machine, everything works fine.

Both systems are running latest CentOS 7.

I'm looking forward to your response.

Thank you!

Best Answer

After a lot of investigations and trials, I have finally find the solution to my own question.

Just to post it here in case others are having the same issue:

What I did was only adding a single line in /etc/sysconfig/network

IPV6FORWARDING=yes

And after a restart of the network using "service network restart", suddenly the issue was completely solved.

FYI, the file /etc/sysconfig/network should has four lines now:

NETWORKING_IPV6=yes
NETWORKING=yes
IPV6FORWARDING=yes
HOSTNAME=[***host name***]

Related Solutions

IPv6 routing problem

Unless your provider really routes your subnet to your host, you'll have to setup your host so that it proxies ICMPv6 neighbourhood discovery (ND) for the IPs of your guests.

Assuming you have been assigned 2001:0DB8:A::/64, your host is 2001:0DB8:A::1 on eth0, and your guest VM uses 2001:0DB8:A::2 (on a virtual bridge br0). To tell your host to proxy ND queries issue the following command:

ip -6 neigh add proxy 2001:0DB8:A::2 dev eth0

Also make sure that you have fowarding and ND proxying enabled for IPv6:

sysctl -w net.ipv6.conf.all.forwarding=1
sysctl -w net.ipv6.conf.all.proxy_ndp=1

On the guest, you either use the link-local address of the host on br0 as default gateway. Or you add an additional IP on the br0 interface on the host, and use that as default gateway in the guests.

Linux – IPv6 works only after ping to routing box

Are the clients' prefixes being manually assigned? Usually they should automatically find the router via Neighbor Discovery Protocol (during which the router sends out advertisements and assign them prefixes automatically), but it sounds like that step might be missing.

Additionally, the router advertisement should be including its link-layer address as an option in the ICMP header of the router advertisement. If this field is missing, the client won't know how to send data to the router. It sounds like this could be the case. The client doesn't know how to reach the router, until it sends out the Neighbor Discovery message and it receives an Neighbor Advertisement from the router (with the router flag in the ICMP message set).

To include the source link layer address in your router advertisements, add the following into your radvd.conf

AdvSourceLLAddress on;

Best Answer

Related Solutions

IPv6 routing problem

Linux – IPv6 works only after ping to routing box

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