TFTP between IBM-PC, 4.2, Wollongong...

[ben]

  We are having some problems using the MIT PC/IP package to do file
transfers using TFTP with both a vanilla 4.2BSD VAX and with Wollongong
software under VAX-VMS. The symptoms are different. First of all I must
say that TELNET works correctly between all machines, so there is no
basic hardware problem. Also, we are using the very latest MIT release
dated Jan. 21, 1985.
1.  With the 4.2 VAX, the PC complains of a UDP checksum error in the first
 TFTP data block it sees from the VAX, so things don't get very far...
 I suspect 4.2 UDP may be involved, not the PC, as this problem does not
 occur when running the PC with the Wollongong. Also, the Wollongong VAX
 does not seem happy either with the 4.2 VAX doing TFTP (though it doesn't
 say explicitly there is a checksum error--it just sulks). The 4.2 VAX,
 needless to say, does TFTP happily enough to itself (when a few higher-
 level bugs are fixed). How can this be? Well, I believe 4.2 does
 not itself check incoming UDP checksums unless the integer "udpcksum" (a
 global integer defined in "udp_usrreq.c") is set nonzero, which I do not
 believe is ever done in the vanilla 4.2 code. So an error on UDP output
 checksumming in 4.2 seems possible. The code is highly inscrutable !!!!!

	    Soooo.. QUESTION NO. 1:

   Is there a known bug in 4.2 UDP output checksumming??

2.  With the Wollongong software, a TFTP transfer begins OK, but the first
 time the VAX ACKs a data block received from the PC, the ACK is rejected
 by the PC, and thus constant retransmissions occur. This seems to be a
 higher level problem altogether...

		    QUESTION NO. 2:

   Anyone out there using Wollongong with PC/IP and getting further?

	 Ben M. Segal,  CERN-DD,  1211 Geneva 23,  Switzerland.
	 {seismo}!mcvax!cernvax!ben