[NANOG] Microsoft.com PMTUD black hole?

Wed May 7 22:07:06 UTC 2008

Nathan Anderson/FSR wrote:
> Nevertheless, the person I have been in contact with is naturally not 
> the final decision-maker on this issue and is going to continue to pass 
> the issue on up the chain of command for me.  So although this issue is 
> not over and I do not have a final verdict from MS yet, I felt that, 
> given that I don't know how much time to expect to pass between now and 
> when that final verdict is rendered, it would be appropriate to let 
> everybody here know what I have learned thus far.  Hopefully public 
> dissemination of this information factoid will prevent others in a 
> position similar to mine from having to helplessly beat their heads into 
> their keyboards.

Let's also not ignore the generally overworked IT administrator at any 
small or medium sized enterprise. He/she may not be (as many folks I've 
run into are) of the mistaken impression that ICMP *is* bad and leaves 
you vulnerable to all sorts of things like SMURF. There are even tools 
out there that "test" your vulnerability by "pinging" you and do other 
investigations.

I know of a tool that a major financial institution uses when certifying 
your networks security -- that scrapes the version number from your 
ESTMP banner to decide whether you comply or not (and other banners). 
(Rather than actually testing for a specific vulnerability). Simply 
blocking all of these packets from their test host gives you a high 
passing score; possibly a perfect one. [Irony and humor aside...]

Many non-SP IT folks think they understand TCP, grudgingly accept UDP 
for DNS from external sources and think everything else is bollocks. 
Many *might* have a fit if they saw Microsoft accepting ICMPs because 
that seems inconsistent with their knowledge of turn-the-knob network 
security. To their view, their Linksys/Netgear/whathaveyou COTS 
firewalls block everything too.

I don't think I'm exaggerating here.

Just a thought, not saying its a good one or whose fault it is...

Deepak Jain
AiNET