Re: [Taps] TAPS Transports and ICMP

["Pal Martinsen (palmarti)" <[e-mail]>]

On 04 Jun 2015, at 22:56, Joe Touch <[e-mail]<mailto:[e-mail]>> wrote:



On 6/4/2015 12:51 PM, Pal Martinsen (palmarti) wrote:

On 04 Jun 2015, at 21:17, Joe Touch <[e-mail]<mailto:[e-mail]>> 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.

*existing*

That means we need to document WHAT IS before deciding to pursue WHAT
SHOULD BE.

ICMP is an *existing* protocol. Not a transport protocol, but a service(?) that affects how the other protocols behaves.

All I am observing is that this is something app developers rarely cares about, and having sections in the TAPS transports draft describing it might help. Why are there sections describing TCP, they could just read RFC 793?


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.


No, but pointing out that there are differences out there and app developers should take care and investigate is a useful hint.

Unfortunately how to do this varies from OS to OS:
See https://tools.ietf.org/html/draft-martinsen-tram-stuntrace-01#appendix-A.2 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.


That I agree on. The discussion is probably better had over a beer. I do feel that it is important that IETF do take into account what is actually used in the wild.


...
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 4.1.3.3.

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 4.2.4.1).

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:
http://stackoverflow.com/questions/4888285/send-an-udp-packet-and-receive-an-icmp-response-from-router-in-c

Yes, I cited code example earlier.

The above code does not fly so well unless you have administrative privileges.

I did a series of tests a while back. Code that works on OS-X, Linux and IOS can be found here:
https://github.com/palerikm/ICMPTest

Have code for windows as well, but that adds another layer of complexity and weirdness.

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:
https://books.google.com/books?id=ptSC4LpwGA0C&pg=PA249&lpg=PA249&dq=socket+errors+icmp&source=bl&ots=Ks3APlbjQs&sig=aBvReFfOYShEGtJtvEheG-8HpnI&hl=en&sa=X&ei=lLpwVdLHJZSZoQSxtYKwCw&ved=0CDMQ6AEwAg#v=onepage&q=socket%20errors%20icmp&f=false

AFAICT, this is widely supported.

We apparently live in two different realities. Figuring out how this work and implementing cross platform application code that does this is not trivial.

The above book does not describe how recent linux kernels handles ICMP.


.-.
Pål-Erik

...
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.

Joe