Re: LCP echo request/reply support over multilink interface (RFC 1990)

At 03:32 PM 3/9/2010 -0500, James Carlson wrote:
>Ignacio Goyret wrote:
>> No, the remote peer is not required to respond to the Echo-Request
>> on the bundle (meaning, with MP headers).
>> 
>> If you make any assumption based on not receiving a response in
>> this case (other than the remote didn't answer), you are writing
>> code that it is not interoperable.
>
>I tend to agree with the sentiment, especially so as I think LCP
>Echo-Request on the bundle is a mostly silly idea, but the documents
>don't seem to say the same thing.
>
>RFC 1990 says only that you MAY send LCP Echo-Request (et al.) on the
>bundle.  It doesn't say anything at all about whether response is
>required or optional or what.  RFC 1661, however, says that response to
>LCP Echo-Request is mandatory.
>
>Obviously, RFC 1661 applies at the per-link level, but what about LCP
>messages at the bundle level?  When using RFC 1661's message atop an RFC
>1990 bundle, is the response required or not?  You're saying "no," but
>I'm not sure all implementors would agree.

Precisely.

My point is that you can't make an assumption based on whether
the remote replied or not your Echo-Request at the bundle level.

If it did, great.

But if it didn't, it doesn't mean anything beyond that the remote
didn't send an Echo-Reply, a choice that is perfectly legal given
the ambiguities in RFC1990.

Some implementors may choose to respond to an Echo-Request at
the bundle level, others may choose to not respond -- and both
implementations would interoperate successfully so long as
there are no assumptions about required responses.

It is a basic application of the "be liberal in what you accept"
principle.

Cheers,
-Ignacio

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