RE: [cobalt-users] Cube 3 - email problems

[flash22@xxxxxxx]

On Thu, 7 Jun 2001, Josh Gasber wrote:

> >Josh Gasber wrote:
> >>
> >> We are using a Cube 3 to handle all of our outbound mail relay and have
> >>         Problems sending email with attachments
> >
> >Will DeHann wrote -
> >
> >Mis-matched duplex settings on any connection between Qube and clients
> >can cause the timeout in sending mail that you're experiencing.
> >
> Will,
> 
> The cube is sitting on a 10bT hub. That hub is uplinked to another 10bT hub
> which is connected to a Cisco 2610 router which is connect to Frame Relay
> over Frac-T1 (384k to the cloud) The remote side is connect via 64k line to
> the cloud, Cisco 1600 router and then 10bT hub.
> 
> The troubling fact is that this exact same setup is used to connect to
> multiple remote sites, in the exact same configuration, none of which is
> experiencing the same problem.
> 
> Does this change anything or help you in any way point me at some trouble
> shooting ideas.

Josh,

 I think Will has hit a very likely problem , i have seen the same problem
elsewhere, see if you can dig up docs / specs on the hubs and make sure
they are really full-duplex cabable. A lot of low-cost hubs, particularly
the 10Bt ones are not really full-duplex.
 The fact that you can send externally
just reinforces this suspiscion, packets going outside will be spaced
apart timewise because your internal lan speed is greater than the
external link speed, the only case where you are saturating the internal
link is sending from the client to the qube, which is exactly the case
where a
half duplex hub trying to manage a fullduplex data stream would start to
barf, as the ACK packets coming back will collide with the outgoing data
packets. Because of the way TCP handles collisions, once this starts to
happen, the errors just start piling up , it can take hours for a small
transfer to finish under this condition, the client will likely timeout
and give up long before this.
 The fact that small emails work is just due to the fact that a
certain quantity of data is sent before the other end ACK's back , so in
effect , you are only sending packets one direction at a time (half
duplex) ...[the magic size here is usually around 32-65K of streamed data]

gsh