Diagnostics

The following information is applicable within the SCADA environment. Use a cmd prompt to run the following commands:

Ping

Ping is a basic command that helps you check out the basics of your network. When pinging another machine, a sequence of special ICMP (Internet Control Message Protocol) Echo Request packets are sent. The receiving machine responds with an echo reply.

The ping program reports a number of items including: the number of milliseconds it took to get a reply to each Echo Request packet, the maximum, minimum and average round trip times, the number of dropped packets and a TTL (Time To Live) value.

• The average round trip time provides an indication of the speed of your network. In general, it's best if round-trip times are under 200 milliseconds. The maximum and minimum round-trip times give you an idea of the variance ('jitter'). When large variance is present, you may experience poor response in communications.

• The number of dropped packets may be an indication of network problems.

• The TTL value helps you find out how many routers (or "hops") the packet goes through in order to get to its destination. Every packet sent has a TTL field set to an initial number (for example 128). As the packet traverses the network, the TTL field is decremented by one, by each router. If the TTL field in successive pings is different, it could indicate that the reply packets are traveling through different routes.

Tracert

Tracert traces the path followed by a packet from one machine to another. The results of this command also provide the IP address of each router the information goes through and how long it took on each hop.

Reviewing the time between hops enables identification of slow or heavy traffic segments: If tracert is unsuccessful, you can use the command output to help determine at which intermediate router forwarding failed or was slowed. Looking for hops that have excessive times or dropped packets in the report from a tracert command can find potential trouble spots between two machines.

Time synchronization

When the network cable is reconnected, the system event viewer may contain a message that the time provider NtpClient is currently receiving valid time data.

This message does NOT mean the computer clock time sync happens. It means the internal clock is adjusted and will act as described in the bullets above. In other words, this message is sent every time the computer is reconnected, but only in certain cases is the actual computer clock also updated to the current Server time.

In other cases, only the internal clock is adjusted and the computer time is gradually synced with server time according to the algorithm.