IOS help, ATM URB and IPv6

Hi NANOGers,

I am looking for some help with a IOS problem.

Got a 7206 VXR NPE-300 with a DS3 ATM interface
and a couple of PA-FE's

its running


This version of IOS solved a critical ATM UBR
cell rate problem, but at the cost of IPv6.

I've tried a stack of other versions all purporting
to support UBR and IPv6. The v6 stuff works, but
UBR breaks by sending cells faster than the ATM
provider will accept and thus drops AAL5 frames.

TAC hasn't been able to get us a good version.

so I'm turning to the wisdom of NANOG for any
ideas on what version to try.

mucho thanks
john brown