Checking the network

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Describing how to troubleshoot network problems could probably fill an entire volume. Therefore, here you find a selection of useful commands to verify the configuration and the connectivity between the systems. You also find a list of commands to check the existence and location of dynamic VIPAs and the actual routing.

Note: You can issue these commands from different environments, such as: z/OS® operator commands (OPER) format, TSO commands, and z/OS UNIX commands.

Checking the configuration

First, check the setup. The following command performs a basic consistency check:

TSO:  HOMETEST

The following commands display the network configuration and attributes.

OPER: D TCPIP,,N,CONFIG
TSO: NETSTAT CONFIG
z/OS UNIX: netstat -f

These commands allow you to verify your specifications in the TCP/IP profile. In particular, check the following settings:

FORWARDING YES
IGREDIRECT 1
SOURCEVIPA 1
PATHMTUDSC 1

Note: If you use multiple TCP/IP stacks, you have to specify the name of the stack as the second parameter in the operator commands, as shown in the following example:

D TCPIP,TCPIPA,NE,CONFIG

Checking network devices

The following commands list the status of the interfaces:

OPER: D TCPIP,,N,DEV
TSO: NETSTAT DEV
z/OS UNIX: netstat -d

From these commands, you can see the device status (for example, READY) and important facts such as whether it is configured as the PRI router (CFGROUTER), and whether it is currently used as the PRI router (ACTROUTER).

The next commands display the status of the interfaces, from an OSPF point of view:

OPER: D TCPIP,,OMPR,OSPF,IFS

Once you know the name of the interface from the second column of the display, you can gather more details by specifying the interface name as an additional parameter on this command:

OPER: D TCPIP,,OMPR,OSPF,IFS,NAME=<interface>

The DESIGNATED ROUTER for this interface is the router that makes all routing table changes for this interface (LAN) and broadcasts them. Of further interest are the STATE, the MAX PKT SIZE, and the number of NEIGHBORS and ADJACENCIES.

Dynamic VIPA

The following command displays the location and status of all VIPAs in the sysplex:

OPER: D TCPIP,,SYSPLEX,VIPADYN

In the z/OS UNIX environment, use the following command to display the list of home addresses (inclusive the VIPAs):

z/OS UNIX:  netstat -h

or just the dynamic VIPAs on the system:

z/OS UNIX:  netstat -v

Routing tables and OSPF

To display routing tables:

OPER: D TCPIP,,N,ROUTE
TSO: NETSTAT ROUTE
z/OS UNIX: netstat -r

To display gateways, you can use:

TSO: NETSTAT GATE
z/OS UNIX: netstat -g

To display OSPF tables:

OPER: D TCPIP,,OMPR,RTTABLE

Apart from the interface display that was previously explained, you may also want to see whether OSPF is talking to its neighbors:

OPER: D TCPIP,,OMPR,OSPF,NBRS

You can even see statistical counters that show the quality of the conversations:

OPER: D TCPIP,,OMPR,OSPF,STATS

On AIX® and Linux® systems, the following command proved to be useful to watch the VIPA takeover among the z/OS systems. The -R option shows the current routing and indicates when the routing changes.

ping -R <hostname>

Checking active connections

To display all active IP connections on the system:

OPER: D TCPIP,,N,CONN

z/OS UNIX: netstat -c (or simply: netstat)

With this command, you also see whether a static or dynamic VIPA is used as a source address or a target address, allowing you to easily verify that the SOURCEVIPA option is effective (that is, for outgoing connections, the VIPA is used as a source address rather than the physical address of the network device).