Re: New Version Notification for draft-herbert-6man-icmp-limits-01.txt

[Tom Herbert <[e-mail]>]

On Mon, May 22, 2017 at 11:47 AM, Ron Bonica <[e-mail]> wrote:
> Hi Tom,
>
> This raises the salient question. When the source IP stack receives a message informing it that HTL has been exceeded, what should it do?
>
> When the source IP stack receives an ICMP PTB message, the required action is well-understood. It should:
>
> - update its estimate of the PMTU associated with the destination of the original packet
> - inform a higher layer protocol if appropriate
> - refrain from sending messages that exceed the PMTU in the future
>
> When the source IP stack receives a message informing it of a HTL violation, what should it do?
>
I think the response would be similar to that described in section 4.
The error should at least be logged and the higher layer protocol
informed. If possible, the headers can be reduced but there is no
deterministic way to do that. It's possible that it was an
encapsulation header that put things over the edge, so if the ICMP
error is received by the encapsulator it's possible that those headers
could be trimmed (for instance be withhold some unnecessary options in
an extensible encapsulation).

Tom

>                                                                     Ron
>
>
>> I don't think HTL should qualify for that special status. The difference
>> between PTB and HTL is the response the sending host(s) take. For PTB the
>> response is deterministic, the sending application should lower its PMTU. But
>> handling of HTL is not deterministic, it may or may not be feasible to reduce
>> headers to fit. The response to HTL might be more on the administrative side
>> like other destination unreachable errors.
>>
>