Implementing PPPoE and Avoiding Fragmentation
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Questions and Answers

What is the standard Ethernet Maximum Transmission Unit (MTU) size in bytes?

  • 1492
  • 1522
  • 1500 (correct)
  • 1600

    • What is the effect of the 8 bytes of PPPoE overhead on the Ethernet MTU?

  • It increases the maximum frame size to 1508 bytes.
  • It has no impact on the MTU size.
  • It requires fragmentation of frames.
  • It reduces the effective MTU to 1492 bytes. (correct)

    • In the output of 'show ip interface brief', which interface is indicated as administratively down?

  • Virtual-Access1
  • Dialer2
  • Serial0/0/0 (correct)
  • GigabitEthernet0/1

    • Which command would be used to verify the encapsulation and MTU size on a Dialer interface?

    <p>show interface dialer 2</p> Signup and view all the answers

    What is the IP address assigned to Dialer2 as per the command output?

    <p>10.1.3.1</p> Signup and view all the answers

    What configuration does the output show regarding the keepalive setting for Dialer2?

    <p>Keepalive is set to 10 seconds.</p> Signup and view all the answers

    What does the line 'line protocol is up (spoofing)' indicate about Dialer2?

    <p>The interface is spoofing its protocol status.</p> Signup and view all the answers

    What is the bandwidth setting displayed in the 'show interface dialer 2' output for Dialer2?

    <p>56 Kbit/sec</p> Signup and view all the answers

    What type of protocol is BGP categorized as?

    <p>Path vector routing protocol</p> Signup and view all the answers

    What is the primary purpose of Internal BGP (iBGP)?

    <p>To distribute routing information learned from eBGP to routers in the same AS</p> Signup and view all the answers

    Which of the following accurately describes the relationship between iBGP and IGP?

    <p>iBGP relies on IGPs to determine the best path but does not perform path calculations.</p> Signup and view all the answers

    What distinguishes External BGP (eBGP) from Internal BGP (iBGP)?

    <p>eBGP exchanges routing information between different autonomous systems, while iBGP does so within the same AS.</p> Signup and view all the answers

    What port does BGP use for its operational communication?

    <p>Port 179</p> Signup and view all the answers

    What role do IGPs play in conjunction with iBGP?

    <p>IGPs calculate the best paths and iBGP only transports the routes.</p> Signup and view all the answers

    What happens to BGP updates transmitted over TCP?

    <p>They are transmitted reliably due to TCP’s connection-oriented properties.</p> Signup and view all the answers

    What does it mean for an AS to be multihomed?

    <p>Connecting to multiple autonomous systems</p> Signup and view all the answers

    Which of the following statements about iBGP is true?

    <p>iBGP only transports routes learned from external sessions within the same AS.</p> Signup and view all the answers

    Under which condition should BGP not be used?

    <p>There is a single connection to the Internet</p> Signup and view all the answers

    What is a drawback of using the Default Route Only BGP option?

    <p>Suboptimal routing due to limited route availability</p> Signup and view all the answers

    Which BGP option allows an organization to forward traffic to the appropriate ISP for networks advertised by that ISP?

    <p>Default Route and ISP Routes</p> Signup and view all the answers

    What is a potential outcome of misconfiguring a BGP router?

    <p>Negative effects throughout the Internet</p> Signup and view all the answers

    Which is NOT a condition for using BGP appropriately?

    <p>Operating with only one connection to the Internet</p> Signup and view all the answers

    What is a primary characteristic of the Default Route and ISP Routes BGP implementation?

    <p>It allows for forwarding traffic based on advertised networks</p> Signup and view all the answers

    Which of the following is a reason for organizations to implement BGP in a multi-homed environment?

    <p>To enhance redundancy and reliability of Internet connectivity</p> Signup and view all the answers

    What is the purpose of the 'ip tcp adjust-mss' command in PPPoE configuration?

    <p>To prevent TCP sessions from being dropped by adjusting the MSS during handshaking</p> Signup and view all the answers

    Which of the following is NOT a potential cause of problems with PPPoE as mentioned?

    <p>Incorrect MTU size setting on the ISP router</p> Signup and view all the answers

    When troubleshooting PPPoE, which command is used to examine the PPP negotiation process?

    <p>debug ppp negotiation</p> Signup and view all the answers

    During which phase of the PPP negotiation process does CHAP authentication occur?

    <p>Authentication Phase</p> Signup and view all the answers

    What does a successful CHAP authentication indicate in the PPP negotiation process?

    <p>The user has entered the correct username and password</p> Signup and view all the answers

    In the provided debugging output, what does the line 'IPCP: Install route to 10.1.3.2' signify?

    <p>An IP address has been successfully negotiated and added to the routing table</p> Signup and view all the answers

    What MTU size is configured on the Dialer2 interface?

    <p>1492</p> Signup and view all the answers

    Which command correctly identifies the BGP peer and its AS number in the eBGP configuration?

    <p>Company-A(config-router)# neighbor 209.165.201.1 remote-as 65001</p> Signup and view all the answers

    Which of the following best describes the function of the IPCP phase in PPP negotiation?

    <p>To negotiate IP address and configuration parameters</p> Signup and view all the answers

    What does the line 'CHAP: Using password from interface CHAP' indicate during PPP negotiation?

    <p>The interface is set to utilize CHAP authentication</p> Signup and view all the answers

    What is one requirement for Company-A to handle all Internet routes effectively?

    <p>Sufficient resources to maintain over 500,000 networks</p> Signup and view all the answers

    What action should be taken if there is a failure in the PPP negotiation process?

    <p>Verify the authentication credentials and MTU settings</p> Signup and view all the answers

    What function does the network configuration command serve in BGP?

    <p>It adds reachable networks to the local BGP table</p> Signup and view all the answers

    In a single-homed BGP topology, what does Company-A do with its internal private IPv4 addresses?

    <p>It translates them to public IPv4 addresses using NAT</p> Signup and view all the answers

    What is the purpose of the AS number in BGP configurations?

    <p>To establish an administrative boundary for routing</p> Signup and view all the answers

    What does ISP-1 typically do in relation to Company-A’s BGP updates?

    <p>Advertises a default route in its eBGP updates</p> Signup and view all the answers

    What is a limitation of advertising all Internet routes to Company-A?

    <p>It demands significant resources and processing power</p> Signup and view all the answers

    How does Company-A ensure optimal routing while receiving multiple ISPs' routes?

    <p>By implementing a path selection algorithm on received routes</p> Signup and view all the answers

    Study Notes

    Ethernet MTU and PPPoE

    • Standard Ethernet MTU is 1500 bytes; adding 8 bytes of PPPoE overhead results in a total frame size exceeding 1500 bytes.
    • Dialer Interface status verification can be done using show ip interface brief, revealing interface statuses such as "up" or "down" for various interfaces.

    PPPoE Configuration Verification

    • Confirm IPv4 address assignment automatically using the show ip interface brief command.
    • Check MTU size on the Dialer Interface with show interface dialer 2, confirming values like MTU of 1492 bytes and encapsulation as PPP.

    Adjusting MSS

    • Use ip tcp adjust-mss 1452 to prevent TCP sessions from being dropped by adjusting the maximum segment size (MSS) during the TCP 3-way handshake.

    Troubleshooting PPPoE

    • Common issues in PPPoE can arise from:
      • Failures in PPP negotiation.
      • Failures in PPP authentication.
      • Incorrect TCP maximum segment size adjustments.

    PPP Negotiation Process

    • Enable troubleshooting for PPP negotiation with debug ppp negotiation, displaying the authentication status of the connection and associated CHAP details.

    Overview of BGP

    • BGP is a path vector routing protocol that utilizes TCP for its updates, ensuring reliable transmission via port 179.
    • BGP is pivotal for inter-AS routing and operates primarily between routers in different autonomous systems (eBGP) or within the same AS (iBGP).

    eBGP vs iBGP

    • External BGP (eBGP) communicates between different autonomous systems, whereas Internal BGP (iBGP) organizes routing information within the same AS.
    • BGP peers or speakers exchange routing information, but eBGP focuses on multiple AS interactions.

    BGP Functionality Distinctions

    • Interior Gateway Protocols (IGPs) distribute routing within a single AS, using metrics like cost and bandwidth to determine paths.
    • iBGP shares externally learned routing information but does not perform path calculations.

    BGP Design Considerations

    • BGP is suited for AS with multiple connections (multi-homed).
    • Avoid using BGP in single-homed scenarios or with limited understanding of the protocol.

    BGP Implementation Options

    • Default Route Only: Simplest method where ISPs provide only default routes, potentially leading to suboptimal routing.
    • Default Route and ISP Routes: ISPs advertise both default and specific routes, allowing for better traffic directing but still possible suboptimal paths.
    • All Internet Routes: Receiving all routes allows precise path selection but demands significant router resources.

    Steps to Configure eBGP

    • Commands to set up eBGP include:
      • router bgp 65000 to define the AS number.
      • neighbor [ip-address] remote-as [number] to identify BGP peers.
      • network [address] mask [subnet] to advertise specific networks.

    Sample BGP Configuration

    • Example configuration for Company-A in AS 65000 advertising its 198.133.219.0/24 network to ISP-1 in AS 65001.
    • Internal devices often use private IPv4 addresses, requiring NAT for public address translation to communicate externally.

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    Description

    This quiz covers essential aspects of implementing Point-to-Point Protocol over Ethernet (PPPoE), with a special focus on avoiding fragmentation issues related to Maximum Transmission Unit (MTU) sizes. It dives into background knowledge of MTU limits and the PPPoE overhead impact on frame sizes. Test your understanding of these crucial networking concepts.

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