FTP problems

[Barry Margolin <barmar@Think.COM>]

    Date: Thu, 5 Nov 1992 14:05 EST
    From: Scott_Busse@mindlink.bc.ca (Scott Busse)

    Thanks for the help with the Secure subnet problems folks. It
    is now working just fine.

    It has opened the door to another problem though. I'm able tolog into
    the Symbolics now, and I can traverse the symbolics directories
    ok, but when I set to binary mode, and try to get a file, it gets
    roughly 28k, as shown in the bottom right of the symbolics host, and
    then just locks up. The message in the Sym window is TYI or Timeout.

"TYI or Timeout" is the wait state of the Peek process, not the FTP
Server, so is not very interesting in this discussion.  You should go
into the "Servers" display of Peek and look at the state of the TCP-FTP
Server process.  My expectation is that it will be in "TCP Out" state,
which means that it's waiting to be able to send on a blocked TCP
connection. 

      The peek window shows that several connections exist between the
    Amiga and the Symbolics, and in case it's useful, here is what it
    says:
    2 connections:
    Host AMFAR ESTABLISHED, local port 20., foreign port 1026.,retransmission
    delay 30.0 seconds.Read acked 14848002., read 1484002., received 1484002.,
    offered limit 14868002  Send acked -568907450., next to send -568903354.,
    imposed limit 14868002 Receive window 20000., send window 0., congestion
    window 2048., congestion threshold T.

Notice the difference between "Send acked" and "next to send" -- the
Amiga hasn't acknowledge the last 4K bytes that the Lispm sent -- and
the send window is 0, meaning that the limit of unacknowledged data that
the Amiga has specified has been reached.

The Amiga is apparently failing to acknowledge this data, or the Lispm
isn't seeing these acknowledgements.  Another clue is that the
retransmission delay is 30 second.  This is initially under a second,
and is increased every time data must be retransmitted (if packets are
being lost due to network overloading, this prevents a feedback loop
that would exacerbate the problem by flooding the network with
retransmissions).  If it makes it all the way up to 30 seconds, there's
something obviously going wrong.

In order to pinpoint the problem, you'll need a network monitor (e.g.
Sniffer or a Sun running etherfind) that can display all the traffic
between the two systems.  If you see the acknowldgement packets being
sent by the Amiga then there's probably a problem on the Lispm
preventing it from receiving them.  If you see the Lispm's data
transmissions but no acknowledgements then there's probably a problem on
the Amiga.

      My guess would be that the congestion threshold T may be significant here.

I don't think so.  It's T on my machine, which is working fine.  I'm not
sure precisely what that flag signifies.

                                                barmar