Re: Anybody else seeing hotmail connections hanging ?

[Eugene Crosser <crosser@rol.ru>]

Matti Aarnio wrote:
> On Thu, Dec 09, 2004 at 02:27:23PM -0300, Carlos G Mendioroz wrote:
> 
>>FYI,
>>the problem was some upstream interface with a small MTU (1480) combined 
>>with some icmp message filtering and hotmail insisting in using DF 
>>(don't fragment) for SMTP, who knows why.
>>
>>We are forcing MSS negotiation down to 1440, and so far so good...
> 
> 
> Ah,  path-mtu-discovery does that, and all modern systems are using it.

Unless ICMP "would fragment" (?) packets are lost on the way for some 
reason.  Pmtu-discovery does not notice the threshold and connection is 
stuck :-(  Happens all the time in VPN or "double NAT" configurations.

Eugene

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