Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!mailrus!tut.cis.ohio-state.edu!ucbvax!YKTVMX.BITNET!ELINSKY
From: ELINSKY@YKTVMX.BITNET ("Jay Elinsky")
Newsgroups: comp.protocols.tcp-ip
Subject: sendmail hanging followup
Message-ID: <8906070114.AA12053@ucbvax.Berkeley.EDU>
Date: 26 May 89 14:57:55 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 21

James B. VanBokkelen writes:

>              ...I have some recent experience with IBM VM systems which
>request 1460 byte MSS regardless of whether the connection is on the local
>subnet, or routed via a gateway. ...

Actually, our VM and MVS TCP/IP programs let you specify the MSS separately
for each route, if desired.  So if some networks are reachable through
gateways that are known to accept large packets, you can tell our TCP to
use large packets for better performance and efficiency. (TCP still respects
the MSS offered by the other end, of course).  Or you can specify the default
size of 576, or even 512 like FTP Software's TCP does, if you aren't sure
that some or all routes can handle larger packets.  If James' recent
experience with an IBM VM system is the one that I remember, the customer's
TCP/IP configuration did specify a larger size for the route through ARPAnet.
I suggested that they use the default size for the route, and I assume that
that fixed the problem.

                                       Jay Elinsky
                                       IBM T.J. Watson Research Center
                                       Yorktown Heights, NY