Hi Tore. > 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
Our managed CPEs (D-Links) send (IPv4 MTU) - 20 bytes in RAs, usually 1480. In the list of "tricks", you might want to add: * Slightly raise the ICMPv6 rate-limit values for your 6RD BR (we do 50/20) I haven't seen IPv6 MSS clamping in the wild yet (it was discussed on this list a year ago). > 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. >From off-the-shelf, we see mostly D-Links and Cisco/Linksys/Belkin with option 212 support. A few Asus models started showing up in the stats in 2013 I believe. Last time I checked, all models supporting option 212 also reduced their MTU properly (YMMV here, that was almost a year ago). Too bigs remain quite common however... #sh ipv6 traffic | in too 11880 encapsulation failed, 0 no route, 3829023354 too big #sh ver | in upt uptime is 2 years, 4 weeks, 5 days, 4 hours, 3 minutes If 6lab's data is right, roughly half of Canada's IPv6 users go through that box (50k users). /JF