Re: [v6ops] 6to4 reliability check

Someone willing to write a NAGIOS plugin?

Frank

-----Original Message-----
From: v6ops-bounces@ietf.org [mailto:v6ops-bounces@ietf.org] On Behalf Of
Pekka Savola
Sent: Friday, February 11, 2011 12:42 AM
To: Brian E Carpenter
Cc: IPv6 Operations
Subject: Re: [v6ops] 6to4 reliability check

On Fri, 11 Feb 2011, Brian E Carpenter wrote:
> "  Unless the answer to all these questions is 'yes', subscribers will
>   be no worse off, and possibly better off, if the route to 192.88.99.1
>   is blocked and generates 'destination unreachable'.  At least one
>   host implementation (Windows XP) starts with a 'ping' to the anycast
>   address, so will quickly learn that 6to4 is not available [Savola]."

I do not know if an (IPv4) destination unreachable will propagate to 
the application (or the stack).  Windows uses the method as a 
qualification procedure (if it doesn't work, the 6to4 relay is not 
used) and as such it won't get reported to the applications in such a 
manner that e.g. ICMPv6 error would be or how you probably hope that 
ICMPv4 would be.

So, I would suggest the following caveat to the former (unless we get 
info on how implementations react -- preferable), and more precise on 
the methodology:

     Unless the answer to all these questions is 'yes', subscribers
     will be no worse off, and possibly better off, if the route to
     192.88.99.1 is blocked and generates an IPv4 'destination
     unreachable'. There is little operational experience with this,
     however.

     Some implementations also perform some form of 6to4 relay
     qualification. For example, a host implementation (Windows) tests
     the protocol-41 reachability by sending an ICMPv6 echo request
     with Hop Limit=1 to the relay, expecting a response or Hop Limit
     exceeded error back. Lack of any response indicates that the 6to4
     relay does not work and it is turned off [Savola].

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings
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