On Feb 15, 2011, at 10:36 54AM, William Herrin wrote:
> On Tue, Feb 15, 2011 at 10:09 AM, Joe Abley <jab...@hopcount.ca> wrote:
>> On 2011-02-14, at 21:41, William Herrin wrote:
>>> On Mon, Feb 14, 2011 at 7:24 PM, TR Shaw <ts...@oitc.com> wrote:
>>>> Just wondering what this community thinks of NIST in
>>>> general and their SP800-119 (
>>>> http://csrc.nist.gov/publications/nistpubs/800-119/sp800-119.pdf )
>>>> writeup about IPv6 in particular.
>>>
>>> Well, according to this document IPv4 path MTU discovery is,
>>> "optional, not widely used."
>>
>> Optional seems right. Have there been any recent studies on how widely pMTUd
>> is actually used in v4?
>
> Hi Joe,
>
> Are you aware of a TCP implementation in an OS that shipped within the
> last decade but doesn't enable IPv4 pMTUd by default? Each version of
> Windows and all the major unixes use it on every TCP connection unless
> you explicitly turn it off.
>
All modern TCPs support it; many firewalls are configured to block the
necessary ICMPs.
--Steve Bellovin, http://www.cs.columbia.edu/~smb
