Re: [tcpm] ICMPv6 Error Handling at TCP draft-fujisaki-tcpm-icmpv6-reaction-00.txt

At 01:36 09/03/2007, Arifumi Matsumoto wrote:

>we've posted an I-D that defines TCP reactions(soft/hard) to ICMPv6 
>error messages.
>This document translates ICMPv4 codes and into ICMPv6 codes in order to define
>soft error / hard error classification for ICMPv6 codes.

We have been talking about ICMP errors on this list for about three 
years now. The direction the industry has taken is to get away from 
tying a specific reaction (basically "abort the connection" or "do 
nothing") to each error message type/code, regardless of e.g., 
connection state.

By translating ICMPv4 codes into ICMPv6 codes you'd basically be 
moving ICMPv6 a number of years back in time. The ICMPv6 spec already 
includes text that gives you freedom in how to respond to ICMPv6 
error messages (e.g., abort a connection in a non-synchronized state 
in response to an ICMP error message, or not abort the connection in 
response to an error message when the connection is in any of the 
synchronized states, or whatever). This freedom already lets you 
implement the soft errors behaviour if you want to address the 
problem of long delays between connection establishment attempts in 
v6 scenarios, as described in the soft errors draft of this WG.

If you translate the ICMPv4 codes into ICMPv6 codes, then:

* For those scenarios in which the lack of v6 connectivity is 
signaled by a so-called "soft error", you won't have solved anything 
(as RFC1122 tells you not to abort the connection attempt).

* For conenctions in the synchronized states, the hard errors would 
open the door to connection-reset attacks, as discussed in the icmp 
attacks draft of this WG.

Implementations have been moving away from the strict type/code -> 
{hard, soft} error classification since more than ten years ago. And 
I honestly think it would be quite a challenge to get the industry 
implement an ICMP error processing policy it has already decided not 
to implement for ICMPv4.

Thanks,

--
Fernando Gont
e-mail: fernando@gont.com.ar || fgont@acm.org
PGP Fingerprint: 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1

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