[c-nsp] 12.2SB PPPoE LAC MTU issue

[Patrick Cole]

Hi all,

I'm running some 7200's terminating PPPoE for BB subscribers. 
The sessions are being forwarded using L2TP to some l2tpns LNS's.

I am experiencing what seems to be an issue with LCP negotiation
with the cisco LAC and the l2tpns LNS causing an mtu mismatch 
in the path for subscribers.  

This issue seems to occur on the 12.2 SB series but not the 
12.3 T series.  I have kept using 12.3 T as a workaround but
would really prefer to use 12.2 SB due to the certain features
and stability improvements.

I havn't tried 12.4 as the boxes do not have a late enough
NPE to support that environment (NPE-400).

My question is, does anyone know 

a) what specifically is different between the way 12.3 T and
12.2 SB perform LCP from a LAC perspective

b) is there a workaround


Regards,

Patrick