OpenVMS Cluster Systems - OpenVMS Systems - HP

Troubleshooting the NISCA Protocol
F.4 Troubleshooting NISCA Communications
F.4 Troubleshooting NISCA Communications
F.4.1 Areas of Trouble
Sections F.5 and F.6 describe two likely areas of trouble for LAN networks:
channel formation and retransmission. The discussions of these two problems
often include references to the use of a LAN analyzer tool to isolate information
in the NISCA protocol.
Reference: As you read about how to diagnose NISCA problems, you may also
find it helpful to refer to Section F.7, which describes the NISCA protocol packet,
and Section F.8, which describes how to choose and use a LAN network failure
analyzer.
F.5 Channel Formation
Channel-formation problems occur when two nodes cannot communicate properly
between LAN adapters.
F.5.1 How Channels Are Formed
Table F–6 provides a step-by-step description of channel formation.
Table F–6 Channel Formation
Step Action
1 Channels are formed when a node sends a HELLO datagram from its LAN adapter to a
LAN adapter on another cluster node. If this is a new remote LAN adapter address, or
if the corresponding channel is closed, the remote node receiving the HELLO datagram
sends a CCSTART datagram to the originating node after a delay of up to 2 seconds.
2 Upon receiving a CCSTART datagram, the originating node verifies the cluster password
and, if the password is correct, the node responds with a VERF datagram and waits for up
to 5 seconds for the remote node to send a VACK datagram. (VERF, VACK, CCSTART, and
HELLO datagrams are described in Section F.7.6.)
3 Upon receiving a VERF datagram, the remote node verifies the cluster password; if the
password is correct, the node responds with a VACK datagram and marks the channel as
open. (See Figure F–2.)
4
WHEN the local node... THEN...
Does not receive the VACK
datagram within 5 seconds
Receives the VACK datagram
within 5 seconds and the cluster
password is correct
The channel state goes back to closed and the
handshake timeout counter is incremented.
The channel is opened.
5 Once a channel has been formed, it is maintained (kept open) by the regular multicast of
HELLO datagram messages. Each node multicasts a HELLO datagram message at least
once every 3.0 seconds over each LAN adapter. Either of the nodes sharing a channel
closes the channel with a listen timeout if it does not receive a HELLO datagram or a
sequence message from the other node within 8 to 9 seconds. If you receive a ‘‘Port closed
virtual circuit’’ message, it indicates a channel was formed but there is a problem receiving
traffic on time. When this happens, look for HELLO datagram messages getting lost.
Figure F–2 shows a message exchange during a successful channel-formation
handshake.
F–16 Troubleshooting the NISCA Protocol