I tried to reply directly to David but it bounced, so let me repost:
 
On Wed, 22 Nov 1995 06:53:22 GMT David D Kaas said:
>We have an HP3000 and are using the NS3000 communications programs.
>I have set up a proxy program on a Sun running solaris 2.3.  The sun
>seems to ignore connections requests from the NS3000 software.  In
>running a sniffer on the network it seems that the NS3000 client,
>nvt, has a zero tcp checksum field.  I have looked at tcp source
>code, tcp_input, and if a packet has a bad checksum it is dropped.
>Does the HP set an incorrect tcp checksum field? or am I missing
>something.
 
 
There is a field in NMMGR that controls checksumming:
 
NMMGR/3000 (B.04.07) #94  Transmission Control Protocol (TCP) Config    Data: Y
When Data Flag is "N", press "Save Data" to create the data record.
Command:
 
 
Path:  NETXPORT.GPROT.TCP
 
 
[N]       Checksum Enabled (Y For Yes, N For No)
 
[4096]    Maximum Number of Connections
 
[2  ]     Retransmission Interval Lower Bound (Secs)
[180  ]   Maximum Time to Wait For Remote Response (Sec)
[10 ]     Initial Retransmission Interval (Secs)
[4  ]     Maximum Retransmissions per Packet
 
[120  ]   Connection Assurance Interval (Secs)
[4  ]     Maximum Connection Assurance Retransmissions
 
By default checksums are disabled.
 
[\] Jeff Kell <[log in to unmask]>