Pascal Hambourg a écrit :
In practice, things are not that simple. The 'route information' option
is not part of the original Router Discovery specification, so older
IPv6 implementations may not support it. Linux supports it since version
2.6.17 if configuration option IPV6_ROUTE_INFO is enabled, but it is
functionnally disabled by default because the sysctl parameters
net.ipv6.conf.*.accept_ra_rt_info_max_plen which defines the maximum
prefix length of accepted route information is set to 0 by default. In
order to accept a route for a /64 prefix, you must set it to at least
64. In Debian it can be set at startup for all interfaces by appending
the following line in /etc/sysctl.conf, assuming that the 'ipv6' module
has been loaded before (.e.g. by adding it in /etc/modules), otherwise
the parameter won't exist yet :
net.ipv6.conf.default.accept_ra_rt_info_max_plen=64
Hmm, looks like this is may not work with a kernel 2.6.21 or later
because entries for interfaces in net.ipv6.conf are created as soon as
the interface is created, whereas older kernels used to create the entry
in net.ipv6.conf only when the interface goes UP for the first time. So
it might be necessary to add
net.ipv6.conf.<interface>.accept_ra_rt_info_max_plen=64 too.
Note :
A similar change was applied to IPv4 interface parameters in
net.ipv4.conf too. However I observed that changing a parameter value in
net.ipv4.conf.default immediately applies to all interfaces which are
not UP, which may preserve the previous behaviour. Unfortunately this
does not work for IPv6 parameters.
If an ethernet host ignores the route information in RAs, it will send
packets for the wireless prefix to the default router, (1). Router (1)
will forward the packets to router (2). It should also send an ICMPv6
Redirect to tell the host that there is a better route to the prefix.
However I tested this scenario on my Debian router with 2.6.24 kernel
and didn't see it sending ICMPv6 Redirects, although it forwarded the
packets back on the same interface as expected.
I think I got it. The RFC 4861 says that the redirect target address
must be the link-local address of the next-hop router, but I had used
the global address of the router in the route. When using the link-local
address instead, the router sends ICMPv6 redirects.
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