Spencer,
On 10/05/2017 05:13, Spencer Dawkins at IETF wrote:
<snip> The bits where we can simply do what you suggest </snip>
> Grrr, but please see below.
>
>>
>>>
>>> I'm really confused by this text.
>>>
>>> Nevertheless, when running within a secure ACP on reliable
>>> infrastructure, UDP MAY be used for unicast messages not exceeding
>>> the minimum IPv6 path MTU; however, TCP MUST be used for longer
>>> messages. In other words, IPv6 fragmentation is avoided. If a node
>>> receives a UDP message but the reply is too long, it MUST open a TCP
>>> connection to the peer for the reply. Note that when the network is
>>> under heavy load or in a fault condition, UDP might become
>>> unreliable. Since this is when autonomic functions are most
>>> necessary, automatic fallback to TCP MUST be implemented. The
>>> simplest implementation is therefore to use only TCP.
Editor hat off.
I agree. I think it's very naive to think that for this application,
intended to be used internally within an enterprise network, in
a NAT-free and proxy-free addressing realm, UDP has any value.
In fact, it's just a nuisance, since the programmer has to do a lot
of the work that TCP does. The performance gain, even if it's real,
is unimportant - autonomic traffic will be a tiny fraction of total
traffic. There will be no gain in footprint, since autonomic nodes
will carry full TCP stacks anyway. [If we wanted to put GRASP in
constrained nodes, we'd probably be talking about GRASP-over-COAP
anyway.] So here's what I would do:
OLD
All other GRASP messages are unicast and could in principle run over
any transport protocol. An implementation MUST support use of TCP.
It MAY support use of another transport protocol. However, GRASP
itself does not provide for error detection or retransmission. Use
of an unreliable transport protocol is therefore NOT RECOMMENDED.
Nevertheless, when running within a secure ACP on reliable
infrastructure, UDP MAY be used for unicast messages not exceeding
the minimum IPv6 path MTU; however, TCP MUST be used for longer
messages. In other words, IPv6 fragmentation is avoided. If a node
receives a UDP message but the reply is too long, it MUST open a TCP
connection to the peer for the reply. Note that when the network is
under heavy load or in a fault condition, UDP might become
unreliable. Since this is when autonomic functions are most
necessary, automatic fallback to TCP MUST be implemented. The
simplest implementation is therefore to use only TCP.
NEW
All other GRASP messages are unicast and could in principle run over
any transport protocol. An implementation MUST support use of TCP.
It MAY support use of another transport protocol, but the details
are out of scope for this specification. However, GRASP itself does
not provide for error detection or retransmission. Use of an
unreliable transport protocol is therefore NOT RECOMMENDED.
END NEW
That doesn't slam the door, but it removes what I now feel is
a very misleading paragraph. Of course, anybody is at liberty to
draft a full description of GRASP-over-UDP as a separate
document.
Again, that was personal opinion. I won't edit that part of
the draft without community input.
Brian
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