Specifications

Chapter 10. LAN notes 111
Figure 10-3 extends this concept to include a tunnel connection between z/OS and the base
Linux.
Figure 10-3 Shared Ethernet and tunnel
The tunnel environment allows connections between Linux TCP/IP applications (such as ftp,
telnet, and x3270) and OSA TCP/IP applications
6
(such as ftp, the TN3270e server that is
part of z/OS communications manager, and so forth). The tunnel environment creates a
virtual adapter similar to an Ethernet adapter. This virtual adapter is assigned its own IP
address on both the Linux and OSA side, as illustrated in Figure 10-3.
We strongly advise that the tunnel IP addresses (for the Linux side and the OSA side) be on a
subnet separate from any other IP addresses involved in the system. We emphasize this in
our documentation by using 10.x.x.x addresses for the tunnel and 192.168.x.x addresses for
other connections.
10.9 Base Linux LAN notes
Messages such as the following:
SFW2-INext-DROP-DEFLT IN=tap0 OUT= MAC= SRC=10.1.1.1 ......
may be seen in the Linux log (with a dmesg command). These messages are related to the
use of multicasting when looking for a DNS name server. The source address indicated in the
message (10.1.1.1) is associated with a tunnel (tap) device in typical zPDT operation and is
unlikely to find a DNS server.
These messages do no harm. If your Linux system has no need to find a DNS server (on any
LAN interface) you can eliminate the messages by editing /etc/host.conf and changing
multi on to multi off.
6
A more exact statement would reference TCP/IP applications within an operating system that is using the
OSA-Express2 interface, of course. In our examples this would be z/OS applications (such as the TN3270e server)
using the z/OS TCP/IP stack that interfaces to OSA-Express2. We abbreviate this detail by simply referring to an
OSA application.
Linux TCP/IP
Linux
System z
ftp user Telnet Browser Telnet
PC system
ftp
Different IP
addresses
One Ethernet port
TSO
ftp
IOS
VTAM
ftp
Telnet server
aws3274
x3270
TCP/IP
Tunnel
Device managers
awsosaawsosa
Note that only a
single Ethernet
port is used here.