Last Updated on September 19, 2021 by Admin 2

300-420 : Designing Cisco Enterprise Networks (ENSLD) : Part 02

  1. Your network consists of one HSRP group of six routers. All of the routers are functioning properly. The network has been stable for several days.In which HSRP state are most of the routers?

    • Learn
    • Listen
    • Standby
    • Active

    Explanation:

    If all of the routers in the Hot Standby Routing Protocol (HSRP) group are functioning properly, then most of the routers in the group are in the listen state. Four routers will be in the listen state, one router will be in the standby state, and one router will be in the active state.

    HSRP is used by a group of routers to create the appearance of a virtual router with which end stations can communicate in the event that the default gateway becomes unavailable. The active router is responsible for forwarding packets that are sent to the virtual router. The standby router is responsible for assuming the role of active router should the active router fail or become unavailable. All other HSRP routers monitor the hello messages sent by the active and standby routers. Should the active and standby routers both become unavailable, the HSRP router with the highest priority is elected to become the active router by default. For routers with equal priority values, the router with the highest IP address becomes the active router.

    HSRP routers can exist in one of the following six states:

    • Initial
    • Learn
    • Listen
    • Speak
    • Standby
    • Active

    All HSRP routers start in the initial state. A router in the learn state is waiting for its first hello message from the active router so that it can learn the virtual router’s IP address. When the hello message is received and the virtual router’s IP address is discovered, the HSRP router is in the listen state. A router in the listen state listens for hello messages from the active and standby routers. If an election for a new active router and a new standby router is required, then an HSRP router will enter the speak state and begin transmitting hello messages. The standby state is reserved for the standby router, and the active state is reserved for the active router. Only routers in speak, standby, and active states will transmit hello packets.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify first-hop redundancy protocols

  2. What command can be used on a Cisco switch to display the virtual MAC address for the HSRP groups of which the switch is a member?

    • switch# show standby mac
    • switch# show hsrp mac
    • switch# show standby
    • switch# show standby brief

    Explanation:

    The command show standby can be used to display the virtual MAC address for HSRP groups of which a switch is a member. This command displays information about HSRP on all configured interfaces and for all HSRP groups. It also displays hello timer information and the expiration timer for the standby switch. The standby switch will take over as the active switch if the timer expires before it hears a heartbeat from the active switch. Below is an example of the show standby command for the HSRP group 1:

    300-420 Part 02 Q02 008
    300-420 Part 02 Q02 008

    In the above output, the following can be determined:

    • The router is currently active for the group, as can be seen in line 2. The Active Virtual MAC address is 0006.6b45.5801, which includes the group number (1) in the last two positions, which is why the address is different from the routers actual MAC address shown on the next line. Special Note: Some router models (Cisco 2500, 4000 and 4500) WILL NOT use this altered MAC address format, but will instead use the real MAC address for the virtual MAC address and will display that MAC address as the virtual MAC address in the output of the show standby command. An example of the output of the show standby command on an older router such as the 2500 would be as follows:
      300-420 Part 02 Q02 009
      300-420 Part 02 Q02 009

    These routers have Ethernet hardware that only recognize a single MAC address. In either case, if for some reason this router becomes the standby router, such as due to loss of interfaces, then when the interfaces come back up it will be able to recover the active role because it is set for preemption, as shown on line 10.

    • The router is tracking two of its own interfaces. Because both interfaces are down, the router’s priority has been reduced by 25 (15 for Fastethernet0/2 and 10 for Fastethernet0/3), from the configured value of 120 to 95. This data is shown on lines 13-16. The default is 10 if not otherwise specified, as is the case for Fastethernet0/3.
    • If either of the two interfaces comes back up, the priority will be increased by the amount assigned to the interface. For example, if Fastethernet0/3 comes back up, the priority will become 105 (95 + 10).
    • The standby router is unreachable, which can be determined because it is marked unknown expired in line 12. This could be due to either a physical layer issue or an HSRP misconfiguration.

    The command show standby brief can be used to view summary information about HSRP groups of which the switch is a member. This information includes the group number, priority, state, active device address, standby address, and group address. It does not include the virtual MAC address.

    The commands show standby mac and show hsrp mac are invalid due to incorrect syntax.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify first-hop redundancy protocols

  3. What command displays detailed information about the GLBP groups to which the switch belongs?

    • switch# show standby
    • switch# show glbp state
    • switch# show glbp
    • switch# show standby detail

    Explanation:

    The command show glbp displays detailed information about GLBP groups on the switch. This information includes the GLBP groups the switch is a member of, whether this is the active switch, the virtual IP address, and whether preemption is enabled. Below is an example of the command output.

    300-420 Part 02 Q03 010
    300-420 Part 02 Q03 010

    The following can be learned from this output:

    • This router is the active virtual forwarder (AVF). In line 3, the output indicates the state is listen. This is the state of the active AVF.
    • As indicated in line 14, this router is configured with a weighting for tracking of 105. It also is configured with an upper limit of 100 and a lower limit of 90. When a tracked object goes down, the value of 105 will be reduced by the decrement value associated with that object. If this results in the weighting dropping below the lower limit (90), this router will give up its role as AVF.
    • The router is tracking two objects, and both have decrement values of 10. This means that ONLY if both objects go down will this router relinquish its role as AVF. As there is another router to take the role of AVF, there will be no disruption of traffic, even if hosts were using the tracked interface that went down.

    The show glbp state will only display the glbp state of the router (standby, listen etc). Detailed output is accomplished with the command show glbp.

    The command show standby can be used to display detailed information about HSRP groups to which a switch belongs. This command is for HSRP only.

    The command show standby detail provides the same output as show standby. It can be used to display detailed information about HSRP groups to which a switch belongs. This command is for HSRP only.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify first-hop redundancy protocols

  4. Which next-hop router redundancy protocol provides backup for an assigned real IP address?

    • HSRP
    • GLBP
    • VRRP
    • CGMP

    Explanation:

    Using VRRP, the shared address of the next-hop router redundancy group can be the real address of a router interface.

    Virtual Router Redundancy Protocol (VRRP) is defined in RFC 2338. VRRP enables a group of routers to form a single virtual router, known as a VRRP group. Routers are configured in VRRP groups to provide redundancy for an IP address shared among members of the VRRP group. This address can be the real address of a router interface or a virtual address (or addresses) shared by the group. Each group is comprised of a master and one or more backup routers. If the shared address is the real IP address of a router, that router will always be the master when the address is available. The master router is responsible for forwarding packets sent to the virtual router. The backup routers provide redundancy and stand ready to assume the role of the master router in the event that it is unable to forward packets.

    The master virtual router owns the VRRP IP address and is responsible for handling all packets sent to the VRRP IP address. Backup VRRP routers monitor for hello activity from the master virtual router. The master router will advertise using IP 224.0.0.18 and MAC 0000.0c00.01xx (xx is the VRRP Group ID). The advertisements by default will be sent every second, and the master down interval is three seconds.

    If the VRRP IP address is NOT the physical address of one of the VRRP routers, then the router with the highest priority will assume the role of the master. The configurable priority range is from 0 to 255, and the default value is 100. The higher the value is, the higher the priority is. If activity stops for the duration of the master router’s down interval, the backup router with the highest priority will become the master router. When the old master router comes back online, it will assume the master role again if it still has the highest priority among all routers.

    In the configuration shown below, Router A will be the master router unless it goes down, in which case B will take over. If A comes back up it will assume the master role again.

    routerA(config-if)# vrrp 3 priority 130
    routerB(config-if)# vrrp 3 priority 110

    Hot Standby Router Protocol (HSRP) defines a set of routers that work together to represent one virtual, fault-tolerant router. Thus, redundancy is provided in the event that any one of the routers fails. The shared address of the next-hop router redundancy group is not the real address of a router interface.

    Gateway Load Balancing Protocol GLBP) is a Cisco-designed protocol that provides for the dynamic utilization of redundant routers in a broadcast network. The shared address of the next-hop router redundancy group is not the real address of a router interface. A virtual group address is used.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify first-hop redundancy protocols

  5. When executed on a HSRP group member named Router 10, what effect does the following command have?

    Router10(config-if)# standby 1 track serial0 25
    • It will cause the router to increase its HSRP priority by 25 if the Serial0 interface on the standby router goes down
    • It will cause the router to shut down the Serial0 interface if 25 packets have been dropped
    • It will cause the router to notify Router 25 is serial 0 goes down
    • It will cause the router to decrement its HSRP priority by 25 if Serial 0 goes down

    Explanation:

    This command will cause the router to decrement its HSRP priority by 25 if Serial 0 goes down. Interface tracking can be configured in Hot Standby Routing Protocol (HSRP) groups to switch traffic to the standby router if an interface goes down on the active router. This is accomplished by having the active router track its interface. If that interface goes down, the router will decrement its HSRP priority by the value configured in the command. When properly configured, this will cause the standby router to have a higher HSRP priority, allowing it to become the active router and to begin serving traffic.

    When the standby router in an HSRP group is not taking over the active role when the active router loses its tracked interface, it is usually a misconfigured decrement value, such that the value does not lower the HSRP priority of the active router far enough for the standby to have a superior priority value.

    The command will not cause the router to increase its HSRP priority by 25 if the Serial0 interface on the standby router goes down. HSRP routers track their own interfaces, not those of another router.
    The command will not cause the router to shut down the Serial0 interface if 25 packets have been dropped. It will only do this if the link becomes unavailable.

    The command will not cause the router to notify Router 25 is serial 0 goes down. The number 25 in the command is the decrement value, not the ID of another router.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify first-hop redundancy protocols

  6. Which statement best describes the interaction between a workstation and an HSRP virtual router?

    • The workstation must have the real IP address of one of the HSRP routers defined as its default gateway.
    • The workstation must support IRDP in order to switch to the alternate router in an HSRP group.
    • The active HSRP router replies to the workstation’s ARP request with the virtual router’s MAC address.
    • The workstation sends packets to the active router’s real MAC address.

    Explanation:

    The active HSRP router replies to the workstation’s ARP request with the HSRP virtual MAC address. The HSRP virtual router presents a consistently available router to the end user, reachable by a single unique, virtual MAC address. Only the active router responds to frames destined to this virtual MAC address, which identifies the HSRP group.

    The primary function of HSRP is to define a set of routers that work together to represent one virtual, fault-tolerant router. Thus, redundancy is provided in the event that one of the routers fails. An HSRP group consists of an active router and a standby router, which together present the appearance of a virtual router. The active router is elected from the routers configured to belong to the HSRP group. The virtual router’s MAC address identifies the virtual router, and the end user will send packets to that destination MAC address. The end-user device will send an ARP request using the known IP address of its default gateway to discover the virtual router’s MAC address. Only the active router will respond to the ARP request. The active router will then forward packets sent to the virtual router. The standby router monitors the status of the HSRP group and assumes packet-forwarding responsibilities of the virtual router if the active router fails.

    The six HSRP states are defined as follows:

    • Initial state: All routers start in this state.
    • Learn state: The router is in the learn state when it has not communicated with the active router. It does not know which router is the active router and does not know the IP address of the virtual router (if no HSRP IP address configured in the router).
    • Listen state: Once the router hears from the active router and knows the virtual IP address, it enters the listen state. It is not the active or standby router.
    • Speak state: After a router learns the IP address of the virtual router, it enters the speak state. It participates in the active and standby router election. It sends hello messages to the active router.
    • Standby state: When the active router has been elected, the second router enters the standby state. This is the standby router and it will become the active router if the active router fails.
      Active state: The router is in active state when it is forwarding packets. It receives packets via the virtual IP address.

    Neither the workstation nor any other device is required to support ICMP Router Discovery Protocol (IRDP) in order to implement an HSRP virtual router. An IRDP-compliant device (RFC 1256) listens for IRDP hello messages, which advertise default routes.

    It is not required for the workstation to know the actual IP address of any of the routers in the group. The end-user device will send an ARP request using the known IP address of its default gateway to discover the virtual router’s MAC address.

    The workstation does not send packets to the active router’s real MAC address. It will send packets to virtual router’s MAC address.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify first-hop redundancy protocols

  7. A company has the following network infrastructure. (Refer to the exhibit.)

    300-420 Part 02 Q07 011
    300-420 Part 02 Q07 011

    Router A is a GLBP active virtual gateway with priority level set to 250. Routers B and C are configured with the default GLPB configurations. The configuration of the active virtual gateway needs to be changed such that if the AVG fails, Router C should be elected to be used as an active virtual gateway. As the network administrator, you have been asked to make corresponding changes to the configuration.

    Which command would you use for this purpose on Router C, and where would the command be configured?

    • glbp 10 preempt (on Router B)
    • glbp 10 preempt (on Router C)
    • glbp 10 priority 200 (on Router B)
    • glbp 10 priority 200 (on Router C)

    Explanation:

    You would configure the glbp 10 priority 200 command on Router C to change the configuration as required. Gateway Load Balancing Protocol (GLBP) gateway priority determines the role that each GLBP gateway plays and what happens if the AVG fails. In the given scenario, Router A is used as an active virtual gateway. If the AVG in a LAN topology fails, an election process takes place to determine which backup virtual gateway should take over. When you configure this command on Router C, Router C will be elected when Router A fails as an AVG.

    Once the configuration change is made, it can be verified by examining the output if the show run command as shown below:

    300-420 Part 02 Q07 012
    300-420 Part 02 Q07 012

    In the above output, it can be determined that the glpb priority 200 command has been applied to the gigabitEthernet0/0 interface on Router C. If the default priority of 100 had been applied, there would be no line in the output for priority. Because Router B is configured with the default configuration, it will have its priority set to the default level as 100.

    You would not use the glbp 10 preempt command on Router B or the glbp 10 preempt command on Router C to change the configuration. You would use this command on a router to enable preemption. Preemption allows a virtual router that was once the AVG to assume its role as active virtual router when it comes back online if it has a higher priority than the current AVG. Alternatively, it can enable a new router with a higher priority to take the role of AVG from the current AVG if the new router has a higher AVG.

    You would use not the glbp 10 priority 200 command on Router B to change the configuration. You would run this command if you needed Router B to be elected as the AVR instead of Router C, as running this command on Router B would configure it with higher priority than Router C.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify first-hop redundancy protocols

  8. Which of the following statements are TRUE about the selection of the active router in an HSRP group? (Choose two.)

    • The router with the highest priority becomes the active router.
    • The router with the lowest priority becomes the active router.
    • The router with the highest IP address becomes the active router if the priorities of all routers are the same.
    • The router with the lowest IP address becomes the active router if the priorities of all routers are the same.

    Explanation:

    The following two statements are TRUE about the selection of the active router in an HSRP group:

    • The router with the highest priority becomes the active router.
    • The router with the highest IP address becomes the active router if the priorities of all routers are the same.

    All routers in an HSRP group have a priority. The default priority of HSRP routers is 100. However, HSRP routers can be assigned any value from 0 through 255 by using the standby priority command. The router with the highest priority becomes the active router of that HSRP group. The active router is responsible for forwarding packets to and from the virtual router (default gateway).

    If the priorities of all the routers in the HSRP group are all the same, then the IP addresses of the routers are considered. The router with the highest IP address of an HSRP interface becomes the active router.

    A standby router is also selected for the HSRP group. When the active router of the HSRP group fails, the standby router becomes the active router. You can decrement the priority of the active router if one of its interfaces goes down if you have enabled tracking for the respective HSRP interface. Interface tracking can be enabled by using the standby track command. By default, the priority of the active router is decreased by 10 when it goes down.

    When the original active router recovers the failed interface, it may become the active router again if the standby preempt command was used on the router. This command specifies that if the router has the highest priority in the HSRP group, then it is immediately selected as the active router for the group. Therefore, if you want the original active router to resume the role when it comes online again, the standby preempt command should be used during its configuration.

    Consider a network segment that has three routers rtrA, rtrB, and rtrC with HSRP enabled all of them. The rtrA router is selected as the active route, while rtrB is the standby router. The partial output of the show running-config command for rtrA is as follows:

    300-420 Part 02 Q08 013
    300-420 Part 02 Q08 013

    The partial output of the show running-config command for rtrB is as follows:

    300-420 Part 02 Q08 014
    300-420 Part 02 Q08 014

    Note that either router will be capable of assuming the role of active router if its priority becomes higher for the following reasons:

    • Decrements in the priority of the active router due to the loss of an interface
    • A manual change in the priorities by the administrator
    • The recovery of a down route that comes back online with a higher priority

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify first-hop redundancy protocols

  9. Which of the following sets of commands CANNOT be included in the plan to implement HSRP on a Layer 3 switch port?

    • interface port-channelno switchport
    • interface fastethernetno switchportip address
    • interface fastethernetswitchport mode access
    • interface vlanip address

    Explanation:

    The following set of commands cannot be included in the implementation plan to configure HSRP on a Layer 3 switch port:

    interface fastethernet
    switchport mode access

    This set of commands creates an access port on the switch. The access port can then be assigned to a VLAN. HSRP cannot be enabled on access ports. To enable HSRP on a switch port, the port has to be any of the following:

    • EtherChannel port Refers to a Layer 3 switch port used for EtherChannel
    • Routed port Refers to a Layer 3 port on a switch used for routing
    • Switch virtual interface (SVI) Refers to a Layer 2 switch port used for inter-VLAN routing

    The interface port-channel and no switchport commands allow you to create a Layer 3 port-channel interface, which can be logically bound with other port-channel interfaces to form an EtherChannel. Port-channel interfaces can be configured as either Layer 2 or Layer 3 interfaces. The interface port-channel command is used to create a Layer 3 port-channel interface.

    The following set of commands creates a routed port:

    interface fastethernet
    no switchport
    ip address

    Routed ports are physical Layer 3 interfaces that allow you to configure a switch as a router. The no switchport command allows the port to be used purely as a Layer 3 port. This command restarts the port thereby deleting any Layer 2 configuration settings on the switch.

    The following set of commands is used to create an SVI, which is a logical interface that allows you to enable inter-VLAN routing on Layer 3 switches:

    interface vlan
    ip address

    SVIs are configured as VLAN interfaces and have at least one physical interface assigned to the VLANs.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify first-hop redundancy protocols

  10. What command provides the output shown below?

    300-420 Part 02 Q10 015
    300-420 Part 02 Q10 015
    • switch# show vrrp brief
    • switch# show standby
    • switch# show glbp
    • switch# show vrrp

    Explanation:

    The command that displays the output in the exhibit is show vrrp. This command displays detailed information regarding VRRP groups on the switch. The information provided for each VRRP group by this command includes the status, virtual IP and MAC addresses, whether preemption is enabled, priority of the switch, and the address of the group master.

    The command show vrrp brief is used to display a summary of the VRRP groups to which the switch belongs. The summary information it provides includes the group number, priority, state, whether preemption is enabled, the Master IP address, and the group IP address.

    The command show glbp displays detailed information about GLBP groups on the switch. This information includes the GLBP groups the switch is a member of, whether this is the active switch, the virtual IP address, and whether preemption is enabled.

    The command show standby can be used to display detailed information about HSRP groups to which a switch belongs. This command displays information about HSRP on all configured interfaces and for all HSRP groups. This command is for HSRP only.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify first-hop redundancy protocols

  11. What command should you use to quickly view the HSRP state of the switch for all HSRP groups of which the switch is a member?

    • switch# show standby brief
    • switch# show ip interface brief
    • switch# show hsrp
    • switch# show standby

    Explanation:

    The command show standby brief should be used to quickly view the HSRP state of a switch for all HSRP groups of which it is a member. The summary information it provides includes the group number, priority, state, active device address, standby address, and group address.

    The command show standby can be used to display detailed information about HSRP groups of which a switch is a member. This command would not provide a quick view. This command displays information about HSRP on all configured interfaces and for all HSRP groups. It also displays hello timer information and the expiration timer for the standby switch.

    The command show ip interface brief is useful in that lists the interfaces and displays the basic IP configuration of each. This output would include the IP address of the interface and the state of the interface, but now HSRP information.

    The command show hsrp is not a valid command due to incorrect syntax.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify first-hop redundancy protocols

  12. Examine the configuration shown below in a partial output of the show run command executed from Router 5.

    300-420 Part 02 Q12 016
    300-420 Part 02 Q12 016

    With this configuration, which of the following is true?

    • if POS 1/0 goes down, Router 5 will become the AVG.
    • if POS 1/0 goes down, Router 5 will relinquish its role as AVG.
    • if POS 1/0 and POS 2/0 go down, Router 5 will relinquish its role as AVG.
    • if POS 1/0 and POS 2/0 go down, Router 5 will become the AVG.

    Explanation:

    If POS 1/0 and POS 2/0 go down, Router 5 will relinquish its role as active virtual gateway (AVG). The example indicates that Router 5 is configured a member of Gateway Load Balancing Protocol (GLBP) group 156 and that it is tracking the state of two of interfaces, POS 1/0 and 2/0. An initial weighting value of 120 has been assigned to the router in line 4, and upper and lower thresholds of 95 and 110 have been configured, respectively.

    In lines 5 and 6, decrement values of 20 and 10 have assigned to the tracking of interface POS 1/0 and POS2/0, respectively. If either of the tracked interfaces goes down, the weight value of the router will be decreased by the amount of the decrement value. If the weight falls below the lower threshold (95), the router will relinquish its role as the AVG. If either single interface that is being tracked goes down, the weight value will not fall below the lower threshold, and the router will maintain its role of AVG. This occurs because 120 – 20 = 100, which is higher than 95 (the lowest threshold), and 120 – 10 = 110, which is also higher than 95. If both interfaces go down, the value will fall below the lower threshold (120 – 10 – 20 = 90, which is lower than 95), and the router will give up its role as the AVG.

    The loss of interfaces will never cause a router to become the AVG. That can only occur if the router functioning as the current AVG in the group loses its interfaces.

    The loss of either of the interfaces alone will not decrement the initial weighting value enough for it to fall below the lower threshold, and therefore will not cause the router to relinquish its role as AVG.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify first-hop redundancy protocols

  13. You need to create an implementation plan for providing Layer 3 redundancy in your switched network. You included Hot Standby Routing Protocol (HSRP) as the protocol to avoid first-hop router failure. However, your supervisor suggests including Virtual Router Redundancy Protocol (VRRP) instead of HSRP in the implementation plan.Which of the following statements is TRUE about the reasons for the suggested change in the implementation plan? (Choose two.)

    • HSRP works only on Cisco routers and VRRP works on both Cisco and non- Cisco routers.
    • HSRP works on both Cisco and non-Cisco routers and VRRP works only Cisco routers.
    • HSRP-enabled routers need to be configured manually to preempt the active router and VRRP-enabled routers preempt it automatically.
    • HSRP-enabled routers automatically preempt the active router and VRRP-enabled routers need to be configured manually to preempt the active router.

    Explanation:

    The following two statements are TRUE:

    • HSRP works only on Cisco routers and VRRP works on both Cisco and non- Cisco routers.
    • HSRP-enabled routers need to be configured manually to preempt the active router and VRRP-enabled routers preempt it automatically.

    HSRP was developed by Cisco intended for only Cisco routers and VRRP was developed by IEFT intended as a standard for routers. HSRP was defined in RFC 2281 and VRRP was defined in RFC 2338. Both these protocols provide a fault tolerance solution by grouping several routers together but presenting them as a single router. One of the routers in the group acts as the active or master router. A second router is selected as the standby router. In case the active or master router fails, the standby router takes over the responsibilities of the active router.

    The router with the highest priority is automatically selected as the active or master router. In HSRP, preempt settings have to be manually configured on every router in the group, even if the routers have a priority higher than that of the active router. However, in VRRP, the routers with higher priority automatically preempt the master router. Another advantage that VRRP has over HSRP is a faster Hello timer (1 second). HSRP has a Hello timer of 3 seconds

    Two other protocols ICMP Router Discovery Protocol (IRDP) and Gateway Load Balancing Protocol (GLBP) provide redundancy for first-hop router failure. IRDP also allows the selection of a new router if the active router fails, while GLBP provides load balancing in addition to redundancy.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify first-hop redundancy protocols

  14. In which HSRP state is the router a candidate to become the next active router for the group?

    • Learn
    • Backup
    • Listen
    • Initial
    • Standby

    Explanation:

    The HSRP router in standby state (the standby router) is a candidate to become the next active HSRP router should the current active router fail.

    The six HSRP states are defined as follows:

    • Initial state: All routers start in this state.
    • Learn state: The router is in the learn state when it has not communicated with the active router. It does not know which router is the active router and does not know the IP address of the virtual router (if no HSRP IP address configured in the router).
    • Listen state: Once the router hears from the active router and knows the virtual IP address, it enters the listen state. It is not the active or standby router.
    • Speak state: After a router learns the IP address of the virtual router, it enters the speak state. It participates in the active and standby router election. It sends hello messages to the active router.
    • Standby state: When the active router has been elected, the second router enters the standby state. This is the standby router and it will become the active router if the active router fails.
    • Active state: The router is in active state when it is forwarding packets. It receives packets via the virtual IP address.

    Backup is not a valid HSRP router state.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify first-hop redundancy protocols

  15. How is load balancing achieved when implementing HSRP?

    • By configuring multiple gateways on the routers
    • By using multiple HSRP groups
    • By configuring the same priority on all HSRP group members
    • By configuring multiple virtual router addresses

    Explanation:

    When implementing Hot Standby Router Protocol (HSRP), load balancing is achieved by using multiple HSRP groups. Routers configured for HSRP can belong to multiple groups and multiple VLANs. By configuring one group to be active for Router A and standby for Router B, and the second group to be active for Router B and standby for Router A, both routers A and B can be used to pass traffic, as opposed to one sitting idle.

    Load balancing cannot be achieved by configuring multiple gateways on the routers. The routers have one IP address. Each group will have a virtual IP address. In the configuration below, line 4 configures the virtual IP address, and is therefore the address that clients will use as their gateway:

    interface fastethernet 0/1
    no switchport
    ip address 192.168.5.5 255.2555.255.0
    standby 1 ip 192.168.5.10

    Load balancing cannot be achieved by configuring the same priority on all HSRP group members. If that were done, one of the routers would become active and the others would remain inactive standbys. The active router will be the one with the highest IP address.

    Load balancing cannot be achieved by configuring multiple virtual router addresses. Each HSRP group can only have one virtual address.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify first-hop redundancy protocols

  16. Which routers comprise a VRRP group?

    • Host and client
    • Master and backup
    • Active and standby
    • Primary and secondary

    Explanation:

    Virtual Router Redundancy Protocol (VRRP) enables a group of routers to form a single virtual router, known as a VRRP group. Routers are configured in VRRP groups to provide redundancy for a virtual IP address shared among members of the VRRP group. Each group is comprised of a master router and one or more backup routers. The physical IP address of the master router will be the virtual IP address of the group.

    The master router is responsible for forwarding packets sent to the virtual router. The backup routers provide redundancy and stand ready to assume the role of the master router in the event that the master is unable to forward packets.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify first-hop redundancy protocols

  17. Which of the following is required to allow load balancing between three HSRP routers connected to the same LAN?

    • A single HSRP group with all three routers as active routers for the group
    • A single HSRP group with one active router for the group
    • Two HSRP groups, each with an active router
    • Two HSRP groups with one active router for both the groups
    • Three HSRP groups, each with an active router
    • Three HSRP groups with one active router for all groups

    Explanation:

    You should configure three HSRP groups on all three routers and select an active router for each of the groups. You can create up to 256 (0 to 255) groups. Each router should be the active router for one of the three groups and the standby router for the remaining two groups.

    If you want to use HSRP on a Layer 3 switch, the switch ports must be one of the following:

    • EtherChannel port Refers to a Layer 3 switch port used for EtherChannel
    • Routed port Refers to a Layer 3 port on a switch used for routing and for inter-VLAN routing
    • Switch virtual interface (SVI) Refers to a Layer 2 switch port used for inter-VLAN routing

    Routed ports are the physical Layer 3 interfaces that allow you to configure a switch as a router. The no switchport command allows the port to be used purely as a Layer 3 port. SVIs are Layer 3 logical interfaces of a switch that allow you to enable inter-VLAN routing on Layer 3 switches. An SVI is configured as a VLAN interface and has at least one physical interface assigned to the VLANs.

    Creating a single HSRP group with all three routers as active routers for the group is incorrect. An HSRP group cannot have multiple active routers; it can have only one active router at a time.

    Creating a single HSRP group with one active router for the group is incorrect because it does not allow load balancing between the three routers. All traffic will be passed through the active router.

    Creating two HSRP groups with an active router each is incorrect because it only allows load balancing between two of the routers and not three of them.

    Creating two HSRP groups with one active router for both groups, or three HSRP groups with one active router for all groups, is incorrect. Doing so does not enable load balancing on all three routers. Only the active router will be used for traffic forwarding.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify first-hop redundancy protocols

  18. Which virtual router states are defined in the GLBP protocol? (Choose two.)

    • Backup gateway
    • Primary gateway
    • Active virtual gateway
    • Active secondary gateway
    • Active virtual forwarder

    Explanation:

    Active virtual gateway and active virtual forwarder are the two states defined in the Gateway Load Balancing Protocol (GLBP). The active virtual gateway (AVG) is elected by the members of the GLBP group. The AVG creates the virtual MAC addresses that are assigned to each of the routers in the group. Each router is responsible for handling packets sent to its virtual MAC address. A GLBP router that forwards packets sent to its virtual MAC address is known as the active virtual forwarder (AVF). GLBP members communicate through hello messages sent every 3 seconds to the multicast address 224.0.0.102.

    The election of the AVG can be influenced by use of the priority command. By default, all routers configured for GLBP have a priority of 100. A higher value indicates a higher priority. The configured priority of a router can be seen in the show run command as shown below:

    300-420 Part 02 Q18 017
    300-420 Part 02 Q18 017

    In the above scenario, all other members of the group were left to the default, which can be determined on those routers by the absence of any priority entry in the show run command. In that case, this router would become the AVG. To remove a priority configuration, execute the nostandby priority command. When this command is executed, the router will revert to the default of 100. When all routers are left to the default, the router with the highest configured IP address will become the active router.

    GLBP is a Cisco-designed protocol that provides for the dynamic utilization of redundant routers in a broadcast network. It differs from HSRP and VRRP in that it is not necessary to configure multiple groups to fully use redundant paths or routers. GLBP has a configurable load-balancing mechanism that will distribute the use of redundant gateways servicing a broadcast network, such as an Ethernet LAN. Each host will have its gateway set to the address of the AVG. When a host issues an ARP to resolve its gateway’s MAC Address, the AVG will respond with the virtual MAC address of a selected AVF. The AVG will perform load balancing by varying which virtual MAC it selects to use in the response. The AVF will own that assigned virtual MAC as long as the gateway is active. If an AVF becomes unable to provide service as gateway, another AVF can assume ownership of the virtual MAC.

    Consider the partial output of the show run command for two routers participating in the GLBP group shown below:

    300-420 Part 02 Q18 018
    300-420 Part 02 Q18 018

    In the above scenario, both routers have the same priority, so Router B will become AVG. Hosts will use a gateway address of 192.168.5.5 (the GLBP virtual address in line 4 of both outputs). When hosts send an ARP message for the MAC address of the gateway, Router B will reply with the MAC address of the next AVF.

    The AVG can be configured to use one of three load-balancing algorithms:

    • Round-Robin Load-Balancing: Using round-robin load- balancing the AVG in turn points to each AVF virtual MAC address in its ARP reply (default method).
    • Weighted Load-Balancing: Using weighted load- balancing, the AVG selects an AVF virtual MAC address to use in the ARP reply proportionally based on the advertised weight value configured in a GLBP gateway.
    • Host Dependant Load-Balancing: Using host-dependant load- balancing, the AVG selects an AVF virtual MAC address to use in the ARP reply based on which one the host used previously. A host will use the same AVF as long as the GLBP group is unchanged.
    • GLBP allows better use of network resources by using the standby router through the load-balancing mechanism. The standby router is an available gateway for the network.

    GLBP and HSRP are Cisco-developed solutions. VRRP is defined in RFC 2338.

    Backup gateway, primary gateway, and active secondary gateway are not terms used when discussing GLBP.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify first-hop redundancy protocols

  19. You are in the process of verifying the operation of your core switches, which are using HSRP. One core switch was left with the default priority; the other was given a lower priority to make it the standby switch. The command show standby brief was executed on one of the switches. Output of the command is shown below:

    300-420 Part 02 Q19 019
    300-420 Part 02 Q19 019

    What does this output mean? (Choose all that apply.)

    • this switch is using the default priority
    • this switch is the active HSRP switch
    • the HSRP devices are up and functioning correctly
    • the switch intended to be the active switch has failed and this switch has taken over
    • preemption is enabled for the group

    Explanation:

    The output in the exhibit indicates that this switch is the active HSRP switch, the switch intended to be the active switch has failed, and that preemption is enabled for the group.

    This is the active switch because Active is the State listed for each interface that is a member of HSRP.

    The question states that the switch that was intended to be the standby switch was given a priority lower than the default. The default priority is 100, so this is not the switch intended to be the active switch. This information indicates that the switch intended to be the active switch has failed.

    Preemption is enabled, as indicated by the P following the priority value in line 2. Since preemption is enabled, the switch with the priority of 100 is still down. When that switch is corrected and joins the group again, it will take over as active.

    The HSRP group is still providing access for users, but not all devices are functioning properly.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify first-hop redundancy protocols

  20. You are troubleshooting a problem with two routers configured in a HSRP group. You intended to configure the routers so that Router A and Router B would each track their respective Fa0/1 interfaces and decrement their priorities for several VLAN groups if the tracked interface went down. However, you find that Router A is not taking over as the active device for the HSRP group on VLAN 101 when the Fa0/1 interface on Router B fails.Which command would NOT be useful for discovering the problem?

    • show running-configuration
    • show vlans
    • show standby brief
    • show standby

    Explanation:

    The show vlans command would NOT be useful for discovering the problem. When troubleshooting a problem with Hot Standby Router Protocol (HSRP), the show vlans command will yield no useful information. The output of the command is shown below, demonstrating that there is no HSRP information provided.

    300-420 Part 02 Q20 020
    300-420 Part 02 Q20 020

    All three of the remaining commands will be useful in discovering information. Each is shown below with an example of its application to troubleshooting.

    Example A:show running-configuration

    Router B is not taking over as the active device for VLAN 101’s HSRP group when the Fa0/1 interface on Router A fails. Below is a partial output of show run for both routers with the output focused on the section concerning VLAN 101’s configuration on each.

    300-420 Part 02 Q20 021
    300-420 Part 02 Q20 021

    The above output displays the source of the problem. Router A has a decrement value of 5 configured for Fa0/1, as shown on the last line of the output after the specification of Fastethernet 0/1. This means that when its Fa0/1 interface goes down, Router A will subtract 5 from its priority for the VLAN 101 group, lowering it to 175. This is still higher than the priority of Router B, which is 170. Therefore, the solution is to change the decrement value for Router A to at least 11. When the interface goes down, Router A’s priority will be decremented to 169, allowing Router B to take the role as active for the HSRP group in VLAN 101.

    Example B:show standby brief

    Router C is not taking over as the active device for VLAN 102’s HSRP group when the Fa0/1 interface on Router D fails. Below is a partial output of show standby brief for both routers C and D, with the output focused on the section concerning VLAN 102’s configuration on each.

    Router C

    Interface Grp Prio P State Active addr Standby addr Group addr
    
    Fa0/1 102 200 Active local 10.10.10.253 10.10.10.251

    Router D

    Interface Grp Prio P State Active addr Standby addr Group addr
    
    Fa0/1 102 200 P Active local 10.10.10.253 10.10.10.251

    The absence of a P in the P (preempt) column in the output for Router C shows that it is not set to preempt. If not configured to preempt, it will never take over for Router D, regardless of its priority with respect to Router D.

    Example C: show standby

    Router F is supposed to be the active router for VLAN 103’s HSRP group. Occasionally both routers are shut down for maintenance over the weekend. After the routers are rebooted, Router F is not taking over as the active device for VLAN 103’s HSRP group. Below is a partial output of the show standby command for both routers, with the output focused on the section concerning VLAN 103’s configuration on each

    300-420 Part 02 Q20 022
    300-420 Part 02 Q20 022

    The output shows that Router F is not assuming the active role because of the priority and decrement values configured on the routers. When both routers go down, Router E will decrement its priority (200) by 10, as shown in last two lines of its output, leaving the priority at 190. Router F will decrement its priority (190) by 50 as shown in last two lines of its output, leaving the priority at 140. Therefore, to ensure that Router F maintains its role as active even after the dual shutdowns, the priority of Router F should be increased to at least 241. When both routers decrement their priorities after shutdown, Router F will then have a priority of 191, which will be higher than the priority value of Router E.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify first-hop redundancy protocols