RE: CPE router acting as host on its WAN interface (RE: draft-ietf-v6ops-ipv6-cpe-router-03.txt WGLC)

["Hemant Singh (shemant)" <shemant@cisco.com>]

Fred,

It's a well-known problem in Linux that the OS incorrectly combined the
Neighbor Cache and the Destination cache causing data forwarding
failures and incorrect on-link assumptions.  This problem you are
alluding to about the IsRouter is another bug in the Linux code as to
why the OS has FIB clearing entries in the Neighbor Cache?  The FIB is
the Prefix List, the Destination Cache, and the Default Router List; the
FIB should not touch the Neighbor Cache.  I do grant you an OS can
independently garbage collect entries in the Neighbor Cache and the OS
is also not non-compliant for ND if the OS deletes entries in the
Neighbor Cache with IsRouter flag set to FALSE.  Note ND RFC 4861 does
not say anything about garbage collecting entries in the Neighbor Cache
with IsRouter flag set to FALSE.   

Now, when anyone reports a bug to me, I try to ascertain the severity of
the bug.  The issue you raise does not look severe to me,  It's a
temporary problem that can fix itself.  If an OS has this garbage
collection nuance and the Neighbor Cache entry is deleted, when the next
packet needs to be sent to the node whose entry was deleted in the SP
rtr, ND address resolution will take place and resolve the address
causing the Neighbor Cache to be populated again. ND also specifies the
packet be held in a queue till the packet's destination is resolved - so
the SP rtr is not likely to drop any packets.

Wes already asked, what if the CE Rtr always sets the IsRouter flag in
ND messages where this flag is possible to be set and that should take
care of your Linux problem.  If the CE Rtr sends an NA, the CE Rtr will
set the IsRouter flag to TRUE. 

Did we miss anything?

Thanks,

Hemant