Chapter 3. Networking 37
3.6.3 Router administration
This router is managed through a browser interface. In our case, we pointed a Linux Web
browser (connected to one of the local LAN ports) to address 192.168.0.1 and received a
logon page from the Web server that is built into the router. The default logon ID for our router
is
admin and the password is password. (You can change these after you log into the router
the first time.)
A number of screens are available to control DHCP functions, firewall filtering, logging, and so
forth. The firewall and logging functions are interesting but are not discussed here. Controls
are also available to assign
service addresses. This requires some understanding.
Suppose an external host, somewhere on the external LAN, attempts to connect to telnet at
address 9.12.6.140 in our example. This is the address of the router. The router has three
systems connected: Linux, z/OS, and Windows. All of these potentially have telnet servers.
What should the router do? There is an administrative screen (via the browser connected to
the router) where you can set relevant controls. For example, you might specify that an
incoming request for telnet should go to the system at 192.168.0.110. If you have not
provided sufficient information for the router to handle this, it would simply discard the
request.
Outgoing requests are not a problem. If our Linux system attempts to telnet to a host at
9.12.3.15, the request is not ambiguous and is sent to that system. The telnet responses back
to the telnet client (in Linux) are automatically handled because the router remembers which
of our local hosts originated the request.
The router offers a Dynamic DNS function (DDNS) that we did not attempt to use. DDNS
assumes that we have assigned system and domain names properly, and this requires some
coordination with whoever manages local system names.
IP addressing plan
We made the following plan for IP addresses in our local LAN. This is an arbitrary plan, but
we found that having a specific plan makes implementation easier. This plan allows for a
variety of guest systems to be attached to our small router. (Since there are only four ports,
we assumed that different systems would be connected at different times.) Our addressing
plan is:
IP Address Use..................................
192.168.0.1 This is the router itself
192.168.0.2-51 Assigned by the DHCP server in the router
192.168.0.52-99 We will manually assign these to any guest systems that need it
192.168.0.100 Linux in our T20 ThinkPad
192.168.0.101 z/OS in our T20 ThinkPad
192.168.0.110 Linux in our T23 ThinkPad
192.168.0.111 z/OS in our T23 ThinkPad
192.168.0.112 Linux for S/390 in our T23 ThinkPad
192.168.0.120 Linux in our xServer system
192.168.0.121 z/OS #1 in our xServer system
192.168.0.122 z/OS #2 in our xServer system
192.168.0.123 Linux for S/390 in our xServer system
192.168.0.124 z/VM in our xServer system
192.168.0.190 OS/2 (in P/390 system #1) (Used as a PCOM client)
Specific configuration (router)
We logged into our router (by pointing the Linux browser in our T23 ThinkPad to 192.168.0.1)
and entered user ID
admin and password password. Using the screens presented by the
browser, we set the following:

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