Re: I-D Action: draft-voyer-6man-extension-header-insertion-02.txt

[Tom Herbert <[e-mail]>]

On Thu, Nov 30, 2017 at 1:25 PM, Robert Raszuk <[e-mail]> wrote:
> Tom,
>
> Imagine the case where packets are subject to go via service chains. I can
> steer the packet to the router which has service nodes connected to it but
> original src address may be used to decide which service given packet is
> subject to take.
>
> Sure I can impose an SR function and map it up front such that the router
> above would never need to inspect src address, but why to construct such
> architecture which only allows limited set of network programming as opposed
> to offer the choice on how to setup things by network operators ?
>
Robert,

Because the architecture, or at least protocol, is not correct.

Suppose a device inserts an EH into a packet that downstream causes
the packet to be dropped and generates an ICMP error which goes back
to the source. What is a source host supposed do with this? It might
be able to determine that it didn't send the EH, and if it's lucky it
might even be able to parse the offending EH and maybe even sees the
problem that caused the error. But then what? How does the host tell
the network to stop mucking with its packets so that they no longer
get dropped and the source host doesn't get blamed?

ICMP handling is just one of several issues that needs to be
addressed. If the only answer is that these aren't concerns because
the protocol is only deployed in controlled networks, then I claim
that's nothing more than hand waving which is not robust and doesn't
scale.

Tom