Components of TCP/IP Networks ICSSCADA Practice Questions (Page 9)

Questions 41–45

1. 41expert · hard

   A SCADA engineer is troubleshooting a file transfer between an engineering workstation and a data historian. The transfer is large and must be reliable, but it is failing intermittently. The engineer notices that the TCP receive window on the historian is frequently zero. What is the most likely cause of the transfer failures?

   • AThe network is dropping packets, causing TCP to retransmit continuously.
   • BThe workstation's TCP checksum is incorrect, causing the historian to discard segments.
   • CThe historian's receive buffer is full, so it is advertising a zero window and the sender must pause.
   • DThe workstation is using UDP, which does not support flow control.
   Reveal Solution Discussion Select an answer first
2. 42application · medium

   A control system engineer is troubleshooting a new PLC that cannot communicate with the SCADA server. The PLC and server are on different subnets. The engineer verifies that both devices have valid IP addresses and subnet masks, and the routing table on the server shows a default route to the gateway. However, the PLC's ARP cache does not contain an entry for the server. What is the most likely cause of the communication failure?

   • AThe PLC is configured with a subnet mask that is too broad, causing it to send the packet directly to the server instead of the gateway.
   • BThe server's ARP cache is full, so it cannot learn the PLC's MAC address.
   • CThe server's default route is incorrect, so it cannot send a reply to the PLC.
   • DThe PLC is missing a default gateway, so it cannot route packets to the server's subnet.
   Reveal Solution Discussion Select an answer first
4. 43expert · hard

   A security engineer is designing a firewall rule set for an OT network. The network has a SCADA server that must communicate with PLCs on a separate subnet using a proprietary protocol over TCP port 502. The engineer wants to allow only the SCADA server to initiate connections to the PLCs, and block all other traffic. Which firewall rule should be applied?

   • AAllow all TCP traffic between the SCADA server and PLC subnet.
   • BAllow inbound TCP 502 from the PLC subnet to the SCADA server.
   • CAllow inbound TCP 502 from the SCADA server to the PLC subnet, and block all other traffic.
   • DAllow outbound TCP 502 from the SCADA server to the PLC subnet, and block all other traffic.
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5. 44application · medium

   A network engineer is designing a new OT segment for a wind farm. The segment will have 50 turbines, each with a PLC that needs a static IP address. The engineer wants to use a private IPv4 subnet that provides enough addresses for the turbines and allows for up to 20 additional devices in the future, while keeping the subnet as small as possible to limit broadcast traffic. Which subnet mask should be used?

   • A255.255.255.0 (/24)
   • B255.255.255.224 (/27)
   • C255.255.255.192 (/26)
   • D255.255.255.128 (/25)
   Reveal Solution Discussion Select an answer first
6. 45foundation · easy

   Which of the following correctly lists the four layers of the TCP/IP model in order from top to bottom?

   • AApplication, Internet, Transport, Network Access
   • BNetwork Access, Internet, Transport, Application
   • CApplication, Transport, Internet, Network Access
   • DTransport, Application, Internet, Network Access
   Reveal Solution Discussion Select an answer first