Hi Rahul,
Please accepy my apologies as I had been reliably informed by the Centos engineer that a default gateway had been applied. I did quesiton him several times to check. The last time he informed me there was NO default gateway. Well, now there is a default gateway and I can ping it from the LNS. So, now we have the next issue (we will get this working with your expert help Rahul 
)....
The client config on the RADIUS is set to the ae0 interface of the LNS as IPv4....... we need it to dual stack really..... when I look at the wireshark trace I see a malformed packet and I think it is because an IPv4 accept is being sent back.
So, on the RADIUS, while running radiusd -X I see the authenticaiton packet arrive and it is accepted, but on the PPP Client I see the LCP packets being dropped and the Wireshark showing "malformed packets"..... could this because of an issue between IPv6 pool on the LNS and the client on the RADIUS being IPv4?
Thanks
Clive