OSPF DR/BDR election is a process that occurs on multi-access data links. It is intended to select two

OSPF nodes: one to be acting as the Designated Router (DR), and another to be acting as the Backup

Designated Router (BDR). The DR and BDR are responsible for generating network LSAs for the multi-

access network and synchronizing the LSDB with other routers on the same network1.

The DR/BDR election is based on two criteria: the OSPF priority and the router ID. The OSPF priority

is a value between 0 and 255 that can be configured on each interface participating in OSPF. The

default priority is 1. A priority of 0 means that the router will not participate in the election and will

never become a DR or BDR. The router with the highest priority will become the DR, and the router

with the second highest priority will become the BDR. If there is a tie in priority, then the router ID is

used as a tie-breaker. The router ID is a 32-bit number that uniquely identifies each router in an OSPF

domain. It can be manually configured or automatically derived from the highest IP address on a

loopback interface or any active interface2.

In this scenario, all routers have the same priority of 1, so the router ID will determine the outcome

of the election. The router IDs are shown in the exhibit as RID values. The highest RID belongs to R4

(10.10.10.4), so R4 will become the DR. The second highest RID belongs to R3 (10.10.10.3), so R3 will

become the BDR.

Reference:

1: OSPF DR/BDR Election: Process, Configuration, and Tuning 2: OSPF Designated Router (DR) and

Backup Designated Router (BDR)

According to the OSPF protocol, the designated router (DR) is the router that acts as the focal point

for exchanging routing information on a multi-access network segment, such as a LAN1. The DR

election process is based on the following criteria, in order of precedence1:

The router with the highest OSPF priority becomes the DR. The default priority is 1, and a priority of 0

means the router will not participate in the election.

If there is a tie in priority, the router with the highest router ID becomes the DR. The router ID is a 32-

bit number that uniquely identifies a router in an OSPF domain. It can be manually configured or

automatically derived from the highest IP address of a loopback interface or a physical interface.

If there is a tie in router ID, the router that was first to become an OSPF neighbor becomes the DR.

In your scenario, two routers share the same highest priority and start time. This means that they

have equal chances of becoming the DR based on the first and third criteria. Therefore, the second

criterion will be used to break the tie, which is the router ID. The router with the highest router ID

will become the DR, and the other router will become the backup designated router (BDR), which is

ready to take over the role of DR if it fails1.

The correct answer to your question is

C. Option

C. Here is why:

Option C shows the configuration of the chassis statement, which defines the properties of the

router chassis, such as the number of aggregated Ethernet interfaces, the number of FPCs, and the

number of PICs1.

To enable aggregated Ethernet interfaces on a router, you need to specify the aggregated-

devices statement under the chassis statement and set the ethernet parameter to the desired

number of interfaces2. For example, to enable two aggregated Ethernet interfaces, you can use the

following configuration:

chassis { aggregated-devices { ethernet { device-count 2; } } }

Option C shows this configuration with the device-count set to 2, which will enable two aggregated

Ethernet interfaces on the router. The other options do not show this configuration and will not

enable any aggregated Ethernet interfaces on the router.

Therefore, option C is the correct answer to your question.

In OSPF, the state of the neighbor relationship is determined by the exchange of OSPF packets

between routers1. The state “2Way” as shown in the exhibit indicates that bi-directional

communication has been established between the two OSPF routers1. This is the normal state for a

neighbor that is not the Designated Router (DR) or Backup Designated Router (BDR) on a broadcast,

non-broadcast multi-access (NBMA), or point-to-multipoint network1. These neighbors are often

referred to as "DRothers"1. Therefore, option B is correct.

The management IP address of a device is the IP address that is used to access the device for

configuration and monitoring purposes. It is usually assigned to a dedicated management interface

that is separate from the data interfaces. The management interface can be accessed via SSH, Telnet,

HTTP, or other protocols.

In the exhibit, the list of interfaces and their statuses shows that the management interface is me0.

This interface has an admin status of up, a protocol status of inet, a local address of

172.23.12.100/24, and a remote address of unspecified. This means that the me0 interface is active,

has an IPv4 address assigned, and is not connected to another device.

Therefore, the management IP address of the device shown in the exhibit is 172.23.12.100.

Reference:

: [Management Interfaces Overview] : [Displaying Interface Status Information]

In this scenario, you should create an aggregate route1. Aggregate routes are used for advertising

summarized network prefixes1. They help minimize the number of routing tables in an IP network by

consolidating selected multiple routes into a single route advertisement1. This approach is in

contrast to non-aggregation routing, in which every routing table contains a unique entry for each

route1.

Therefore, option A is correct. Options B, C, and D are not correct because:

Static route using the resolve feature: This type of route uses the resolve feature to install a static

route in the routing table only if a specific condition is met1. However, it does not provide the

capability to summarize multiple routes into a single prefix.

Generate route: This type of route generates a route that is always present in the routing table and

can be used to summarize routes. However, it does not have the capability to only advertise the

route when specific BGP routes are being received from a neighbor1.

Static route using qualified next hops: This type of route allows for the specification of multiple next-

hop addresses for a static route1. However, it does not provide the capability to summarize multiple

routes into a single prefix.

Thank you for your visit.

A is correct because RSTP alternate ports block traffic while receiving superior BPDUs from a

neighboring switch. An alternate port is a backup port for a root port, which means it receives better

BPDUs from another bridge than the current root port1. However, an alternate port does not forward

any traffic, as it is in a discarding state2. It only listens to BPDUs and waits for the root port to fail. If

the root port fails, the alternate port can immediately transition to a forwarding state and become

the new root port1.

C is correct because RSTP alternate ports provide an alternate higher cost path to the root bridge. An

alternate port is selected based on the same criteria as the root port, which are the lowest bridge ID,

the lowest path cost, the lowest sender port ID, and the lowest receiver port ID3. However, an

alternate port receives a higher cost BPDU than the root port, otherwise it would be the root port

itself1. Therefore, an alternate port provides an alternate higher cost path to the root bridge than the

root port.

On Juniper switches, the default VLAN is set to a VLAN ID of 1 by default12. This means that all

interfaces on the switch are members of VLAN 1 until they are specifically assigned to another

VLAN12. Therefore, option A is correct.

The default VLAN ID can be changed12. This allows network administrators to configure the switch to

use a different VLAN as the default, if necessary12. Therefore, option D is correct.

The exhibit shows the output of the command show ospf neighbor, which displays information about

the OSPF neighbors on a router1.

The output shows that the OSPF neighbor with the address 172.26.1.1 and the interface ge-0/0/3.0 is

in the Exstart state1.

The Exstart state is the fourth state in the OSPF neighbor formation process, after Down, Init, and 2-

Way states2. In this state, the OSPF neighbors establish a master-slave relationship and exchange

database description (DBD) packets, which contain summaries of their link-state databases2.

The most common reason for OSPF neighbors to be stuck in the Exstart state is an MTU mismatch

between the interfaces3. MTU stands for maximum transmission unit, which is the largest size of a

packet that can be transmitted on a network segment4. If the MTU values of two OSPF neighbors are

different, they may not be able to exchange DBD packets successfully, as some packets may be

dropped or fragmented due to their size exceeding the MTU limit3.

To solve this problem, you need to ensure that the MTU values of both OSPF neighbors are the same

or compatible. You can use the command show interfaces to display the MTU value of an interface5.

You can also use the command ping with the do-not-fragment option to test the MTU size between

two routers. You can change the MTU value of an interface by using the command set interfaces

interface-name mtu mtu-value in configuration mode5.

The DHCP snooping feature in Juniper Networks’ EX Series switches works by building a binding

database that maps the IP address, MAC address, lease time, binding type, VLAN number, and

interface information1. This database is used to filter and validate DHCP messages from untrusted

sources1.

However, there are certain conditions that could prevent entries from being automatically created in

the snooping database for an interface:

MAC limiting: If MAC limiting is enabled on the interface, it could potentially interfere with the

operation of DHCP snooping. MAC limiting restricts the number of MAC addresses that can be

learned on a physical interface to prevent MAC flooding attacks1. This could inadvertently limit the

number of DHCP clients that can be learned on an interface, thus preventing new entries from being

added to the DHCP snooping database.

Static IP address: If the device connected to the interface is configured with a static IP address, it will

not go through the DHCP process and therefore will not have an entry in the DHCP snooping

database1. The DHCP snooping feature relies on monitoring DHCP messages to build its database1,

so devices with static IP addresses that do not send DHCP messages will not have their information

added.

Therefore, options B and C are correct. Options A and D are not correct because performing a

DHCPRELEASE would simply remove an existing entry from the database1, and Dynamic ARP

inspection (DAI) uses the information stored in the DHCP snooping binding database but does not

prevent entries from being created1.