User manual

Microsoft Windows™
12
(Single-interface setup)
Most usual configuration under Windows is single-interface set-up as pictured below:
In this set-up VAX instance binds virtual DELQA or DEQNA (XQ) via
pcap to NIC and uses this binding to
send and receive Ethernet packets both to/from remote nodes and to/from the host machine.
Some newer NICs can implement TOE (TCP off-load-engine) processing. Such adaptors cannot be used for
communication between VAX instance and host machine, but only for communication between VAX and
remote nodes. If your system uses TOE adapter and you want VAX to be able to communicate with he
host machine, you will need to use dual-homed set-up described in the next section. Alternatively, you
can install additional adapter in host machine, such as perhaps USB adapter, that does not use TOE, and
bind XQ to this adapter.
Gigabit Ethernet networks may use jumbo frames of size exceeding conventional Ethernet’s 1514-byte
packet size limit. DEQLA and DEQNA interfaces and OpenVMS VAX software cannot handle such frames.
Therefore VAX MP is unable to communicate with machines that send jumbo frames, including possibly
the host machine itself. If you need to comminicate with those machines using protocols that do actually
utilize large MTU, disable jumbo frame use in your network. Alternatively, install second adapter in your
machine, such as perhaps USB adapter, disable use of outgoing jumbo frames on this adapter and connect
it to the network via a switch that performs translation of incoming jumbo frames to regular-sized frames,
then bind XQ to this adapter. However for protocols that are configured to use only smaller MTU and only
send packets fitting into 1514-byte frame, operating on mixed-frame network is possible. In particular,
TCP can be configured (and in home networks connected to DSL or cable modem commonly is) to use
MTU of 1492 or 1500, rather than large MTU and thus limiting the size of Ethernet packets with TCP traffic
to 1514 bytes.