IPv6 support in ppp is built-in. It should be enabled.
Note: unfortunately, I don't have a dial-up environment to test this, but certain
other distros have enabled it so I doubt there's that much harm for ipv4 users
at any rate.
.src.rpm at http://www.netcore.fi/pekkas/linux/ipv6/ for reference.
I can have a whole /48 ipv6 network, thanks to my isp and i really would like my
rhl to be able to handle it "natively".
I can confirm that pppd can be both ipv6 and ipv4 without any problem.
Please verify this with a newer version of Red Hat Enterprise Linux or Fedora
Core and reopen it against the new version if it still occurs.
Closing as "not a bug" for now.