Troubleshooting
Problem
The TCPIP stack has two (or more) devices connected on the same LAN. It is expected that one of these devices will always have ARP responsibility for the VIPAs active on that stack. However, when displaying the device status, that device is not always listed as the owner.
Symptom
A NETSTAT DEVLINKS command shows the following output near the end of the report:
EZZ2826I IPv4 LAN Group Summary
EZZ2827I LanGroup: 00001
EZZ2828I LnkName LnkStatus ArpOwner VipaOwner
EZZ2829I ------- --------- -------- ---------
EZZ2771I LINK2 Active LINK2 Yes
EZZ2771I LINK1 Active LINK1 No
The expected output is:
EZZ2826I IPv4 LAN Group Summary
EZZ2827I LanGroup: 00001
EZZ2828I LnkName LnkStatus ArpOwner VipaOwner
EZZ2829I ------- --------- -------- ---------
EZZ2771I LINK1 Active LINK1 Yes
EZZ2771I LINK2 Active LINK2 No
Cause
The VipaOwner is determined at device startup. If two devices are on the same LAN, the first one to start communicating on that LAN is assigned ownership of ARP responsibility for all VIPAs on the stack. When both devices are being started as a part of TCPIP initialization, then a race involving several asynchronous events for both devices results in this determination. All devices are equally capable of being the owner, and (for a properly configured network) there is no other externally visible effect one way or the other.
This function has been performed on all z/OS releases; it is only on z/OS 1.8 and later that the result is reported in the NETSTAT output.
Resolving The Problem
No action is required; the system is operating normally. If there is a nontechnical reason that one device should always be the owner (with the exception of device failure cases), then do the following:
- Remove the START statement for the second device from the TCPIP PROFILE.
- Add automation that is triggered by the EZB6473I message and issues a VARY TCPIP,,START,devicename command for that second device.
NOTE: This ensures only the order of activation at TCPIP startup. If the device having ownership goes down for some reason, the VipaOwner will move to the other device and stay there as long as it remains active (even when the first device is restarted).
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Document Information
Modified date:
15 June 2018
UID
swg21430261