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Miscellaneous Questions

March 16th, 2020 in ENCOR 350-401 Go to comments

Question 1

Explanation

The time kept on a machine is a critical resource and it is strongly recommend that you use the security features of NTP to avoid the accidental or malicious setting of incorrect time. The two security features available are an access list-based restriction scheme and an encrypted authentication mechanism.

Reference: https://www.cisco.com/c/en/us/support/docs/availability/high-availability/19643-ntpm.html

Question 2

Explanation

In this question, the inside local addresses of the 10.1.1.0/27 subnet are translated into 209.165.201.0/27 subnet. This is one-to-one NAT translation as the keyword “overload” is missing so in fact answer B is also correct.

Question 3

Explanation

SW1 needs to block one of its ports to SW2 to avoid a bridging loop between the two switches. Unfortunately, it blocked the fiber port Link2. But how does SW2 select its blocked port? Well, the answer is based on the BPDUs it receives from SW1. A BPDU is superior than another if it has:
1. A lower Root Bridge ID
2. A lower path cost to the Root
3. A lower Sending Bridge ID
4. A lower Sending Port ID

These four parameters are examined in order. In this specific case, all the BPDUs sent by SW1 have the same Root Bridge ID, the same path cost to the Root and the same Sending Bridge ID. The only parameter left to select the best one is the Sending Port ID (Port ID = port priority + port index). And the port index of Gi0/0 is lower than the port index of Gi0/1 so Link 1 has been chosen as the primary link.

Therefore we must change the port priority to change the primary link. The lower numerical value of port priority, the higher priority that port has. In other words, we must change the port-priority on Gi0/1 of SW1 (not on Gi0/1 of SW2) to a lower value than that of Gi0/0.

Question 4

Explanation

The difference between on-premise and cloud is essentially where this hardware and software resides. On-premise means that a company keeps all of this IT environment onsite either managed by themselves or a third-party. Cloud means that it is housed offsite with someone else responsible for monitoring and maintaining it.

Question 5

Explanation

The IP protocol was designed for use on a wide variety of transmission links. Although the maximum length of an IP datagram is 65535, most transmission links enforce a smaller maximum packet length limit, called an MTU. The value of the MTU depends on the type of the transmission link. The design of IP accommodates MTU differences since it allows routers to fragment IP datagrams as necessary. The receiving station is responsible for the reassembly of the fragments back into the original full size IP datagram.

Fragmentation and Path Maximum Transmission Unit Discovery (PMTUD) is a standardized technique to determine the maximum transmission unit (MTU) size on the network path between two hosts, usually with the goal of avoiding IP fragmentation. PMTUD was originally intended for routers in IPv4. However, all modern operating systems use it on endpoints.

The TCP Maximum Segment Size (TCP MSS) defines the maximum amount of data that a host is willing to accept in a single TCP/IP datagram. This TCP/IP datagram might be fragmented at the IP layer. The MSS value is sent as a TCP header option only in TCP SYN segments. Each side of a TCP connection reports its MSS value to the other side. Contrary to popular belief, the MSS value is not negotiated between hosts. The sending host is required to limit the size of data in a single TCP segment to a value less than or equal to the MSS reported by the receiving host.

TCP MSS takes care of fragmentation at the two endpoints of a TCP connection, but it does not handle the case where there is a smaller MTU link in the middle between these two endpoints. PMTUD was developed in order to avoid fragmentation in the path between the endpoints. It is used to dynamically determine the lowest MTU along the path from a packet’s source to its destination.

Reference: http://www.cisco.com/c/en/us/support/docs/ip/generic-routing-encapsulation-gre/25885-pmtud-ipfrag.html (there is some examples of how TCP MSS avoids IP Fragmentation in this link but it is too long so if you want to read please visit this link)

Note: IP fragmentation involves breaking a datagram into a number of pieces that can be reassembled later.

If the DF bit is set to clear, routers can fragment packets regardless of the original DF bit setting -> Answer D is not correct.

Question 6

Explanation

The TCP Maximum Segment Size (TCP MSS) defines the maximum amount of data that a host is willing to accept in a single TCP/IP datagram. This TCP/IP datagram might be fragmented at the IP layer. The MSS value is sent as a TCP header option only in TCP SYN segments. Each side of a TCP connection reports its MSS value to the other side. Contrary to popular belief, the MSS value is not negotiated between hosts. The sending host is required to limit the size of data in a single TCP segment to a value less than or equal to the MSS reported by the receiving host.

TCP MSS takes care of fragmentation at the two endpoints of a TCP connection, but it does not handle the case where there is a smaller MTU link in the middle between these two endpoints. PMTUD was developed in order to avoid fragmentation in the path between the endpoints. It is used to dynamically determine the lowest MTU along the path from a packet’s source to its destination.

Reference: http://www.cisco.com/c/en/us/support/docs/ip/generic-routing-encapsulation-gre/25885-pmtud-ipfrag.html (there is some examples of how TCP MSS avoids IP Fragmentation in this link but it is too long so if you want to read please visit this link)

Note: IP fragmentation involves breaking a datagram into a number of pieces that can be reassembled later.

Question 7

Explanation

The logging synchronous global configuration command also affects the display of messages to the console. When this command is enabled, messages appear only after you press Return.

Reference: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3560/software/release/12-2_52_se/configuration/guide/3560scg/swlog.html

Question 8

Explanation

A rendezvous point (RP) is required only in networks running Protocol Independent Multicast sparse mode (PIM-SM).

By default, the RP is needed only to start new sessions with sources and receivers.

Reference: https://www.cisco.com/c/en/us/td/docs/ios/solutions_docs/ip_multicast/White_papers/rps.html

For your information, in PIM-SM, only network segments with active receivers that have explicitly requested multicast data will be forwarded the traffic. This method of delivering multicast data is in contrast to the PIM dense mode (PIM-DM) model. In PIM-DM, multicast traffic is initially flooded to all segments of the network. Routers that have no downstream neighbors or directly connected receivers prune back the unwanted traffic.

Question 9

Explanation

6to4 tunnel is a technique which relies on reserved address space 2002::/16 (you must remember this range). These tunnels determine the appropriate destination address by combining the IPv6 prefix with the globally unique destination 6to4 border router’s IPv4 address, beginning with the 2002::/16 prefix, in this format:

2002:border-router-IPv4-address::/48

For example, if the border-router-IPv4-address is 64.101.64.1, the tunnel interface will have an IPv6 prefix of 2002:4065:4001:1::/64, where 4065:4001 is the hexadecimal equivalent of 64.101.64.1. This technique allows IPv6 sites to communicate with each other over the IPv4 network without explicit tunnel setup but we have to implement it on all routers on the path.

Comments
  1. Ciscolad
    March 18th, 2020

    Question 7
    A network administrator is implementing a routing configuration change and enables routing debugs to track routing behavior during the change. The logging output on the terminal is interrupting the command typing process. Which two actions can the network administrator take to minimize the possibility of typing commands incorrectly? (Choose two)

    A. Configure the logging synchronous global configuration command
    B. Configure the logging delimiter feature
    C. Configure the logging synchronous command under the vty
    D. Press the TAB key to reprint the command in a new line
    E. Increase the number of lines on the screen using the terminal length command

    A is one of the answer but cannot figure out what the other one is? either C or D seems these can be correct.

    C – Use the line vty line-number command to specify which vty lines are to have synchronous logging enabled
    D – If you cannot remember a complete command name, or if you want to reduce the amount of typing you have to perform, enter the first few letters of the command, then press the Tab key. The command line parser will complete the command if the string entered is unique to the command mode. If your keyboard does not have a Tab key, press Ctrl-I instead.

    Anyone can shine a light on this matter?

  2. Ciscolad
    March 21st, 2020

    Which two GRE features are configured to prevent fragmentation? (Choose two)
    A. TCP window size
    B. TCP MSS
    C. IP MTU
    D. DF bit Clear
    E. MTU ignore
    F. PMTUD

    Answer: B F

    I did the exam and got this question , there was no option for PMTUD, answer may fall on IP MTU

  3. brad
    March 21st, 2020

    @ Ciscolad

    Are the questions in this premium membership enough to pass the exam?

  4. karrira
    April 7th, 2020

    I just passed the Test

    I got

    EIGRP Evaluation Sim .. exactly the same
    OSPF SiM .. OSPF process and area were different nothing more
    IPV6 OSPF virtual Link Sim

    all of the questions are found here

    mega.nz/#!eCwwDI7C!759Kp4RuT-XCjrL2luYDjemZ_X1PJtkBq4DKYC7_Qh4

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