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List:       ipng
Subject:    (IPng 4959) Re: IPv6 over ATM encapsulation
From:       bgleeson () cisco ! com
Date:       1997-11-24 6:02:38
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>Francis Dupont and I were just discussing the possibility of removing the=
>null
>encapsulation option from draft-ietf-ion-ipv6-atm-00.txt.
>We think that's a good idea for two reasons:
>- the null encapsulation is fairly limiting and useless =
>- the less options there are, the likelier (and the better) one can =
>interoperate

I will make two points about interoperability 

1) If there is a default (and there is - LLC) which is mandatory
to implement then there is no interoperability problem. 

2) Systems today are required to assume that a remote party may
try to negotiate the encapsulation. That is, a system cannot assume
that in a SETUP there will only be one BLLI element, or that the 
first BLLI element will indicate LLC. It can assume that one of the 
BLLI elements will indicate LLC, otherwise there is a protocol error.
If the negotiation of an alternate encapsulation is prohibited
then this may lead to implementations that assume there will only
be one BLLI element and that it is LLC. This introduces a change
in the IPV4/ATM and IPV6/ATM behaviours which is likely to cause
interoperability problems rather than diminish them, given that
there are likely to be systems that speak both IPV4 and IPV6
and use the same signalling stack.

Bryan


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