S/390 PartnerWorld for Developers, ITSO/EFS Project EFS Systems on a Linux Base: Additional Topics

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: