Re: [tram] Transport of ICMP errors in TURN

[Simon Perreault <[e-mail]>]

Le 2015-08-26 06:29, Marc Petit-Huguenin a écrit :
> During the presentation of the Path MTU Discovery Using STUN draft in Prague, there was some discussion on how ICMP can be received by the client when the PMTUD probes are sent through a TURN server.  Which reminded me that I worked on that problem when I proposed PMTUD over STUN, back in 2008.  That was the case, according to my notes, but in fact the idea of tunneling the ICMP packets through the TURN server was proposed the year before, but for a different reason:
> 
> https://mailarchive.ietf.org/arch/msg/behave/76pAtymXlAtF5SoD0rgoFECf2Fg
> 
> So my proposal is to add this into turnbis.  I can provide text.

RFC 5766 section 2.6 <https://tools.ietf.org/html/rfc5766#section-2.6>
explains that ICMP not being relayed was a design decision to make it
possible to run a TURN server as an unprivileged user. That conclusion
is wrong for two reasons:

- With the BSD sockets API, some ICMP errors are translated into recv()
error codes. This means that it is always possible to relay at least
some subset of ICMP errors. (Not sure for TCP or IPv6, I'd need to check.)

- On Linux, which dominates the market of TURN server, one can receive
all ICMP errors as an unprivileged user with the IP(V6)_RECVERR socket
option.

So my conclusion is: yes, please. :)

Simon