The bridging table is a data structure that stores the MAC addresses and the associated interface details and MAC learned time for each MAC address. The bridging table is used by the switch to forward frames based on the destination MAC address. The ether type details and the preamble of Ethernet packet are not stored in the bridging table, as they are not relevant for the switching process. References:

Enterprise Routing and Switching, Specialist (JNCIS-ENT) - Juniper Networks

Enterprise Routing and Switching, Specialist (JNCIS-ENT) - Juniper Networks

[Junos OS Layer 2 Configuration Guide - TechLibrary - Juniper Networks]

[Junos OS Layer 2 Configuration Guide - TechLibrary - Juniper Networks]

BGP is a routing protocol that operates between autonomous systems (AS). An AS is a group of routers under a single administrative control. BGP can be classified into two types: internal BGP (IBGP) and external BGP (EBGP). IBGP is the BGP communication between routers within the same AS, while EBGP is the BGP communication between routers in different AS. BGP uses the AS_PATH attribute to record the AS numbers that the route has passed through, and uses it to prevent routing loops and select the best path.

In this scenario, you want to add a second ISP connection and remove the default route to the existing ISP. This means that you want to have more control over the routing decisions and use BGP to exchange routes with both ISPs. To do this, you need to deploy the BGP protocol in your network and configure both IBGP and EBGP sessions. The correct statements about BGP in this scenario are:

IBGP peers advertise routes received from EBGP peers to other IBGP peers. This is the default behavior of IBGP, as it allows the routers within the same AS to learn the routes from different EBGP peers and select the best exit point. However, IBGP has a rule that it does not advertise routes received from IBGP peers to other IBGP peers, to avoid creating routing loops. Therefore, option B is correct and option C is incorrect. To overcome this rule, IBGP requires a full mesh topology, where every IBGP router is directly connected to every other IBGP router, or a route reflector or confederation design, where some IBGP routers act as intermediaries to reflect or aggregate the routes to other IBGP routers.

EBGP peers advertise routes received from IBGP peers to other EBGP peers. This is the default behavior of EBGP, as it allows the routers in different AS to exchange routes and reachability information. However, EBGP has a rule that it does not advertise routes received from EBGP peers to other EBGP peers, to avoid creating routing loops. Therefore, option D is correct and option A is incorrect. To overcome this rule, EBGP uses the AS_PATH attribute to filter out the routes that contain its own AS number, or uses route maps or policies to control the route advertisement. IBGP does not update the next-hop attribute to ensure reachability within an AS, as the next-hop attribute is preserved by IBGP. Instead, IBGP relies on an underlying IGP (Interior Gateway Protocol) to provide reachability to the next-hop.

MAC limiting protects against flooding of the Ethernet switching table (also known as the MAC forwarding table or Layer 2 forwarding table). This feature is enabled on interfaces (ports). MAC limiting sets a limit on the number of MAC addresses that can be learned on a single Layer 2 access port. The MAC limit value in the EX-series switch’s default configuration is five MAC addresses. You can configure the MAC limit on an interface, on an interface in a VLAN, or on all interfaces. You can also specify the action to be taken when the MAC limit is exceeded, such as dropping packets, logging messages, or shutting down the interface. Additionally, you can configure specific “allowed” MAC addresses for the access port. Any MAC address that is not in the list of configured addresses is not learned. Allowed MAC binds MAC addresses to a VLAN so that the address does not get registered outside the VLAN. References:

[EX] How to control MAC address access through Junos OS for EX Series switches1

Configuring MAC Limiting2

Understanding MAC Limiting and MAC Move Limiting3

C  is correct because Layer 2 control traffic is permitted on the secondary link of a redundant trunk group (RTG) on EX Series switches.  Layer 2 control traffic includes protocols such as LLDP, LACP, and STP, which are used to exchange information and coordinate actions between switches 1 .  According to the Juniper Networks documentation 2 , Layer 2 control traffic is allowed to pass through both the active and the secondary links of an RTG, but data traffic is only forwarded through the active link. This allows the switches to maintain their Layer 2 adjacencies and monitor the link status on both links.

D  is correct because if the active link fails, then the secondary link automatically takes over in an RTG on EX Series switches.  An RTG consists of two trunk links: an active or primary link, and a secondary or backup link 2 . The active link is used to forward data traffic, while the secondary link is in standby mode.  If the active link fails or becomes unavailable, the secondary link immediately transitions to a forwarding state and takes over the data traffic without waiting for normal STP convergence 2 . This provides fast recovery and redundancy for the network.

Aggregate routes are used for advertising summarized network prefixes 1 2 .  They help minimize the number of routing tables in an IP network by consolidating selected multiple routes into a single route advertisement 1 .  This approach is in contrast to non-aggregation routing, in which every routing table contains a unique entry for each route 1 .

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

Aggregate routes can be used with both static routing and dynamic routing protocols 1 .

Aggregate routes are not automatically generated for all of the subnets in a routing table.  They need to be manually configured 1 .

Aggregate routes are not always preferred over more specific routes.  The route selection process in Junos OS considers several factors, including route preference and metric, before determining the active route 1 .

A  is correct because generated routes require a contributing route.  A contributing route is a route that matches the destination prefix of the generated route and has a valid next hop 1 .  A generated route is only installed in the routing table if there is at least one contributing route available 2 . This ensures that the generated route is reachable and useful.  If there is no contributing route, the generated route is not added to the routing table 2 .

B  is correct because generated routes show a next hop in the routing table.  A generated route inherits the next hop of its primary contributing route, which is the most preferred route among all the contributing routes 2 .  The next hop of the generated route can be either an IP address or an interface name, depending on the type of the contributing route 2 .  The next hop of the generated route can also be modified by a routing policy 3 .

In Rapid Spanning Tree Protocol (RSTP), there are several port roles that determine the behavior of the port in the spanning tree 1 2 3 .  The roles include root, designated, alternate, backup, and disabled 1 2 3 .

The discarding state is associated with the backup, alternate, and disabled roles 1 2 3 .  In a stable topology with consistent port roles throughout the network, RSTP ensures that every root port and designated port immediately transition to the forwarding state while all alternate and backup ports are always in the discarding state 2 .  Disabled ports are also in the discarding state 3 .

Therefore, options B, C, and D are correct.

According to the Juniper documentation 1 , the output of the show vlans command displays the forwarding options for the VLAN, including the DHCP security features. In the exhibit, the output shows that DHCP security is enabled, and that ARP inspection and IP source guard are also enabled. These features work together to protect the switch from IP spoofing and ARP spoofing attacks. DHCP snooping builds a database of IP/MAC bindings by snooping DHCP messages. ARP inspection validates ARP packets against the DHCP snooping database and drops invalid packets.  IP source guard checks the IP and MAC source addresses of packets against the DHCP snooping database and drops spoofed packets 2 3 . Therefore, the correct answer is A, B, and C.

The other options are not correct because:

D. The DHCP snooping database is not protected by default.  To protect the database from corruption or loss, you need to configure a file name and a location for storing the database, and enable periodic write operations to the file 4 . The exhibit does not show any such configuration.

E. DHCP snooping is not enabled for IPv6 traffic by default.  To enable DHCPv6 snooping, you need to configure a DHCPv6 relay agent and specify the trusted interfaces for DHCPv6 messages 5 . The exhibit does not show any such configuration.