MTU handling in 6RD deployments

Emmanuel Thierry ml at
Tue Jan 7 12:56:59 CET 2014


Le 7 janv. 2014 à 12:37, Tore Anderson a écrit :

> 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

For your information, i see an advertised mtu of 1480 on my WiFi interface with the Free CPE.

> * 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.

Best regards
Emmanuel Thierry

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