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I have a problem setting up IPv6 connectivity to two virtual hosts that I run on VmWare workstation. The hosts are CentOS 6.2 x86 and x86-64. Even though they are on a bridged network and there is a RA router on the same segment, they don't accept the advertisment from the router.

I can ping6 the router through its link-local address, cat /proc/sys/net/ipv6/conf/eth0/accept_ra returns 1 and I flushed all the ip6tables rules.

The hosts are both a fresh install and I haven't changed anything apart from installing a few libraries and changing wallpaper ;)

What should I do/check/... ?

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Is /proc/sys/net/ipv4/ip_forward enabled in the VM? If so, then the system will not automatically assign an address. – Zoredache Apr 18 '12 at 18:50
Well, it was set to 1. I will try to disable forwarding and try again. – Tibor Apr 18 '12 at 18:54
That is strange /proc/sys/net/ipv4/ip_forward shows 1, even though in sysctl.conf there is set net.ipv4.ip_forward = 0. How is this possible? – Tibor Apr 18 '12 at 19:07
I know many firewall scripts/tools will enable forwarding for you even if you are just setting up host-based rules. Try doing something like this grep forward /etc/*. You might be able to find what is setting it. – Zoredache Apr 18 '12 at 19:18
Nope, grep does not return anything connected to IP forwarding. – Tibor Apr 18 '12 at 19:32
up vote 1 down vote accepted

Here is the relavent bits from the kernel documentation about forwarding. And Router Solicitations/Advertisements.

forwarding - BOOLEAN
        Configure interface-specific Host/Router behaviour.

        Note: It is recommended to have the same setting on all
        interfaces; mixed router/host scenarios are rather uncommon.


        By default, Host behaviour is assumed.  This means:

        1. IsRouter flag is not set in Neighbour Advertisements.
        2. Router Solicitations are being sent when necessary.
        3. If accept_ra is TRUE (default), accept Router
           Advertisements (and do autoconfiguration).
        4. If accept_redirects is TRUE (default), accept Redirects.


        **If local forwarding is enabled, Router behaviour is assumed.**
        This means exactly the reverse from the above:

        1. IsRouter flag is set in Neighbour Advertisements.
        2. **Router Solicitations are not sent.**
        3. **Router Advertisements are ignored.**
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