LAN Problem

[SSD|tyrol]

     Hello,
     
       I must apologize for such a lengthy message, but I have a problem that
     has me really confused.  I am the novice network administrator for one of
     the HEL's LAN (see LAN below), and have been experiencing a problems with
     transmissions to the MILNET.
     
     LAN
     ---
     
       I maintain a subnet attached to the main BRLNet via a AGS Cisco gateway.
     Attached to this subnet are several types of systems including INTEL 320's,
     VAX (VMS), MAC's, PC's, and an ISI.  The gateway is use to convert TCP/IP
     and 1822 protocols.  The Intel operate with XENIX 3.4 operating system, the
     VAX VMS, and the ISI uses 4.2 BSD UNIX.  Additionally, the INTEL's use
     CMC's TCP/IP board; the VAX uses Wollongong's TCP/IP board and the ISI has
     EXCELAN's board.
     
     The Problem
     -----------
     
       Each system on the subnet (i.e. INTEL's and VAX machines) communicate
     properly with other systems on the MILNET with the exception of the ISI
     machine.  This machine (CCLHD.ARPA IP #192.12.67.20) has difficulty
     communicating with other system on the MILNET when packet size exceed 509
     bytes (the 509 bytes are data size--does not include headers etc.).  When a
     file, exceeding the 509 bytes, is attempted to be transferred (PUT) on
     another system, FTP locks up.  However, the ISI system can 'GET' a file of
     any size (within reason).
       The same occurs with E-mail.  I thought that the problem was the Cisco
     gateway was fragmented packages improperly, however, I have an tmp account
     on STL-HOST1 (a TOP20 system), and I ftp'd a 1500 byte file without an
     error.  I don't feel reassemble of the packages are a problem because I am
     testing this with a couple of BRL machines, and have the problem with both.
     
     Questions
     ---------
     
     Has anyone experienced this?  Do you have a solution?
     Can you provide suggestions?
     
     Thanks,
     
     Ron Spencer
     spencer at hel-fire.arpa