[Netalyzr] IPv6 fragmentation problem reported - but why?

[Nicholas Weaver]

Thanks.  This suggests a bug in our V6 server, such as the MTU discovery server having crashed.

I will attempt to debug this in the next couple of hours.


On Sep 18, 2013, at 9:01 AM, Stefan Winter <stefan.winter at restena.lu> wrote:

> Hello,
> 
> I've just run netalyzr checks on our network. We are an ISP, and have a
> pretty good grasp of all technology involved, and are rather proud of
> our well-implemented and double-checked IPv6 connectivity.
> 
> That's why I was very baffled to see an IPv6 fragmentation problem being
> reported. It's test 44 of this client-side transcript:
> 
> http://n1.netalyzr.icsi.berkeley.edu/transcript/id=43ca253f-2716-4ddc7253-7ffa-40c8-87ef/side=client/sort
> 
> It shows that IPv6 fragments can be sent and received between my host
> and Netalyzr just fine. The tool then goes on to try and find the MTU on
> the IPv6 link and its binary search goes down to MTU = 0. ?!?
> 
> Given that we're able to send and receive packets at all, the 0 looks
> rather impossible to me.
> 
> The log is not verbose enough for me to figure out *what* exactly this
> test is doing though, and if there's anything we might need to fix.
> 
> I did, of course, check the obvious candidate: yes, ICMPv6
> packet-too-big is allowed bidirectionally on both of the firewalls this
> test traverses. After those comes the backbone, which is out of my reach.
> 
> If someone cares enough to take a look at this, I'd very happy.
> 
> Greetings,
> 
> Stefan Winter
> 
> -- 
> Stefan WINTER
> Ingenieur de Recherche
> Fondation RESTENA - Réseau Téléinformatique de l'Education Nationale et
> de la Recherche
> 6, rue Richard Coudenhove-Kalergi
> L-1359 Luxembourg
> 
> Tel: +352 424409 1
> Fax: +352 422473
> 
> PGP key updated to 4096 Bit RSA - I will encrypt all mails if the
> recipient's key is known to me
> 
> http://pgp.mit.edu:11371/pks/lookup?op=get&search=0xC0DE6A358A39DC66
> <0x8A39DC66.asc>_______________________________________________
> Netalyzr mailing list
> Netalyzr at mailman.ICSI.Berkeley.EDU
> http://mailman.ICSI.Berkeley.EDU/mailman/listinfo/netalyzr


--
Nicholas Weaver                  it is a tale, told by an idiot,
nweaver at icsi.berkeley.edu                full of sound and fury,
510-666-2903                                 .signifying nothing
PGP: http://www1.icsi.berkeley.edu/~nweaver/data/nweaver_pub.asc


-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 841 bytes
Desc: Message signed with OpenPGP using GPGMail
Url : http://mailman.ICSI.Berkeley.EDU/pipermail/netalyzr/attachments/20130918/656b0be6/attachment.bin