MTU handling in 6RD deployments

Tore Anderson tore at
Tue Jan 7 12:37:39 CET 2014

Hi list,

Does anyone know what tricks, if any, the major 6RD deployments (AT&T,
Free, Swisscom, others?) are using to alleviate any problems stemming
from the reduced IPv6 MTU? Some possibilities that come to mind are:

* Having the 6RD CPE lower the TCP MSS value of SYN packets as they
enter/exit the tunnel device
* Having the 6RD BR lower the TCP MSS value in the same way as above
* Having the 6RD CPE advertise a lowered MTU to the LAN in RA Options
* Several (or all) of the above in combination

Also, given that some ISPs offer [only] Layer-2 service and expect/allow
their customers to bring their own Layer-3 home gateway if they want
one, I would find it interesting to learn if any of the most common
off-the-shelf home gateway products (that enable 6RD by default) also
implement any such tricks by default or not.


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