Re: [Taps] TAPS Transports and ICMP

Joe Touch <> Thu, 04 June 2015 20:56 UTC

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From: Joe Touch <>
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Subject: Re: [Taps] TAPS Transports and ICMP
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On 6/4/2015 12:51 PM, Pal Martinsen (palmarti) wrote:
>> On 04 Jun 2015, at 21:17, Joe Touch <> wrote:
>> On 6/4/2015 12:08 PM, Pal Martinsen (palmarti) wrote:
>> ...
>>>> UDP passes all ICMP messages to the app. If the app doesn't listen for
>>>> it, that’s the app's decision.
>>> Then there is a lot UDP application developers out there that does not care. 
>>> Ill guess what I am asking if we should make life easier for them.
>> Again, FIRST this doc needs to explain the current abstract APIs for
>> transport protocols.
>> THEN we can decide whether that set either needs to be augmented,
>> diminished, or translated to be more useful for “applications".
> Heh.. I still do not get that..
>>From the Abstract:
> This document describes services provided by existing IETF protocols
> and congestion control mechanisms.


That means we need to document WHAT IS before deciding to pursue WHAT

> It is designed to help
> application and network stack programmers and to inform the work of
> the IETF TAPS Working Group.
> Having a description of how ICMP works. Both in theory (abstract
> APIs) and in practice would help app developers.

In theory, it behaves like RFC 792 and RFC 1122 specify.

In practice, we can measure whether those capabilities are supported or
not (but that's not particularly the scope of TAPS).

However, that does not necessarily require documenting the Java
interface to TCP on Linux CentOS v7. That what man pages are for.

>>>>> Unfortunately how to do this varies from OS to OS:
>>>>> See for
>>>>> examples.
>>>> You are confusing the OS and language-dependent implementation of the
>>>> API with the abstract API.
>>> On purpose. I hate it when a feature should work because it says so 
>>> in a RFC, but the implementations of it is so vastly different that
>>> it is not possible to get the thing to work so the app developer just
>>> chose to ignore it.
>> The IETF standardizes protocols and abstract APIs.
>> If you are concerned with differences in the implementations of those
>> abstract APIs, you need to address them in other organizations (e.g.,
>> POSIX, etc.).
> That seems like a fun task.. (So who is on the list: Apple,
> Microsoft, Google(android), Linux, BSD…)

POSIX is maintained by the IEEE, and defines the common API across
various OS implementations - and yes, some of those orgs participate.

That's far outside the scope of the IETF, though.

>> ...
>>>> RFC1122 requires that UDP implementations make the ICMP signals
>>>> available to the application. It does not indicate by what mechanism.
>>>>> Listening for port unreachable can be nice to avoid spamming a host or
>>>>> application that recently crashed. Detecting fragmentation or max MTU is
>>>>> also a nice feature especially VoIP applications sending video can
>>>>> utilise to optimise their packet sizes. 
>>>> UDP is required to pass ALL ICMP messages to the app layer, as per RFC 1122.
>>> That is another problem. An app using port 5555 will receive all
>>> ICMP messages also generated by other apps running on other ports.
>> That's an incorrect implementation. See RFC1122 Section
> The section says:
> UDP MUST pass to the application layer all ICMP error
> messages that it receives from the IP layer.  Conceptually
> at least, this may be accomplished with an upcall to the
> ERROR_REPORT routine (see 
> Section
> Looks like none the implementers do send any ICMP messages to the
> UDP layer.

Here's an example of how an app can get errors in response to a call:

The app can get async errors (i.e., not in response to a given sendmsg
or recvmsg call) by using a connect() to the socket - i.e., creating a
handle by which the OS can signal the app.

See the book excerpt here:

AFAICT, this is widely supported.

>> ...
>>> So this boils down better education of the app developers?
>> No, in that case you have a bug. The only thing the UDP app has to worry
>> about are ICMPs from other apps using the same port.
> Do you have any real code to show that this actually work as described on any platform?

See above.