Hi Rémi,
On 05/03/2010 14:33, Rémi Després wrote:
Until PMTUD is made reliable in IPv6 (btw an important objective), all
IPv6-enabled hosts should have their MTU set to 1280 to avoid IPv6 blackholes.
This could in principle apply only to IPv6 packets that leave customer sites,
but as long as hosts have only one MTU parameter, it has to apply to all
packets.
Since typical hosts have longer default MTUs than 1280, advertising MTU=1280 on
links that offer paths to the global Internet appears to be the only available
tool at hand.
The proposal is then to replace:
"A 6rd CE SHOULD advertise the 6rd Tunnel MTU, whether determined automatically or
configured directly, on the LAN side by setting the MTU option in Router Advertisements
[RFC4861] messages to the 6rd Tunnel MTU."
by:
"As long as the path MTU discovery has not been made reliable, a 6rd CE SHOULD
advertise on the LAN side, in the MTU option of Router Advertisements [RFC4861], an MTU
of 1280 octets . This is to prevent that longer packets that could have traversed the
local 6rd domain may be discarded, because of their size, further in the Internet because
of their size. Note that this may cause all hosts attached to the link to use a reduced
MTU even for link-local communications, IPv6 and IPv4."
I'm not sure I see how adopting this approach makes meeting your
'important objective' any more likely.
- Mat
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