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Peers recognize each other’s ability to use MP-BGP extensions by advertising the ability using the capabilities field during the session establishment. MP-BGP is an extension to BGP that allows BGP to carry routing information for multiple network layer protocols, such as IPv6, VPNv4, multicast, etc. To support MP-BGP, peers need to exchange their capabilities during the session establishment phase, which consists of three steps: open, keepalive, and update. In the open message, peers can include an optional parameter called capabilities, which indicates what kind of address families and subsequent address families they can support. If both peers agree on a common set of capabilities, they can proceed to exchange routing information for those address families using update messages56.

References: Use of MP-BGP Extensions for IPv6 Interdomain Routing, MP-EBGP Configuration Example - Cisco

Regarding the BGP decision algorithm, two statements that are correct are:

A higher local-preference attribute will be favored over a lower local-preference attribute. The local-preference attribute is used by BGP routers within an AS to indicate their preference for an exit point from the AS. A higher value means a more preferred path. The local-preference attribute is exchanged only between iBGP peers and does not leave the AS boundary89.

A path cannot be considered if the next-hop is inaccessible. The next-hop attribute is used by BGP routers to determine where to forward packets for a given destination prefix. The next-hop attribute is usually set to the IP address of the eBGP neighbor that advertises the prefix. If there is no IGP route to reach the next-hop address, the path is marked as invalid and ignored by BGP1011.

The other two statements are incorrect because:

The most important criteria is not the administrative distance, but rather the weight attribute. The administrative distance is used by routers to choose between routes from different routing protocols, not within BGP. The weight attribute is a Cisco-specific attribute that is used by BGP routers to prefer one path over another within the same router. The weight attribute is local to the router and not advertised to any peers1213.

A lower local-preference attribute will not be favored over a higher local-preference attribute, as explained above.

References: BGP Best Path Selection Algorithm - Cisco, Understanding BGP Local Preference Attribute - NetworkLessons.com, BGP Next Hop Attribute Explained - NetworkLessons.com, BGP Next Hop Processing - Cisco Press, BGP Weight Attribute Explained - NetworkLessons.com, Understanding BGP Weight Attribute - Cisco Community

Two roles of the DHCP protocol in a network are:

It is used by hosts to obtain the IP address and other parameters from the DHCP server. DHCP stands for Dynamic Host Configuration Protocol, which is a protocol that provides automatic and centralized management of IP addresses and other network configuration parameters for devices connected to a network. A host that needs an IP address can send a request to a DHCP server, which will assign an available IP address from a pool and lease it to the host for a certain period of time34.

It is used to inform hosts about the default gateway. The default gateway is the IP address of the router that connects the host to other networks. The default gateway is one of the parameters that can be delivered by the DHCP server to the host, along with other parameters such as subnet mask, DNS server, domain name, etc. The host can use the default gateway to send packets to destinations outside of its local network34.

References: What Is DHCP? (Dynamic Host Configuration Protocol) - Lifewire, Dynamic Host Configuration Protocol - Wikipedia

The route type that is restricted in an OSPF stub area is type 5. Type 5 LSAs are external LSAs that are generated by ASBRs to advertise routes from other routing domains or protocols into OSPF. Type 5 LSAs are flooded throughout the OSPF domain by default, except in stub areas. Stub areas are special OSPF areas that block type 5 LSAs from entering the area in order to reduce the size of the LSDB and the routing table. Stub areas only receive information about intra-area routes (type 1 and 2 LSAs), inter-area routes (type 3 LSAs), and a default route (type 3 LSA with destination 0.0.0.0/0) from the ABRs910.

References: Introduction to OSPF Stub Areas - NetworkLessons.com, What Are OSPF Areas and Virtual Links? - Cisco

In the exhibit, the action performed by router R3 for traffic arriving from router R2 towards router R4 is PHP, which stands for penultimate hop popping. PHP is a process in which the penultimate hop router (the router before the egress router) removes the top label from an MPLS packet before forwarding it to the egress router. This reduces the label stack depth of the packet and relieves the egress router from performing a label lookup operation. In the exhibit, router R3 is the penultimate hop for traffic arriving from router R2 towards router R4. Router R3 will perform a PHP operation, removing the top label from the incoming packet before forwarding it to router R478.

References: PHP Tutorial - W3Schools, PHP: Downloads

The code that is commonly used to assign higher priority to VoIP traffic is EF, which stands for Expedited Forwarding. EF is a per-hop behavior (PHB) defined by the Differentiated Services (DiffServ) model for QoS. EF provides low delay, low jitter, and low loss for real-time applications such as VoIP. EF is marked by setting the DSCP value to 101110, which corresponds to decimal 4678. AF31, which stands for Assured Forwarding class 3 low drop probability, is another PHB defined by DiffServ, but it provides lower priority than EF. AF31 is marked by setting the DSCP value to 011010, which corresponds to decimal 2678. DF, which stands for Default Forwarding, is a PHB defined by DiffServ that provides best-effort service for unmarked traffic. DF is marked by setting the DSCP value to 000000, which corresponds to decimal 078. AF11, which stands for Assured Forwarding class 1 low drop probability, is another PHB defined by DiffServ, but it provides lower priority than EF and AF31. AF11 is marked by setting the DSCP value to 001010, which corresponds to decimal 1078.

References: Differentiated services - Wikipedia, Solved: Cisco VoIP Phone traffic marking - Cisco Community

The protocol that would be used to bundle multiple Ethernet ports into a virtual link with an aggregated bandwidth is LACP, which stands for Link Aggregation Control Protocol. LACP is a protocol that allows two or more devices to negotiate the formation of a link aggregation group (LAG), also known as an EtherChannel or a port channel. A LAG combines multiple physical links into one logical link that provides increased bandwidth, load balancing, and redundancy. LACP is defined in IEEE 802.3ad and 802.1AX standards12.

References: Link Aggregation Control Protocol - Wikipedia, What is “link aggregation” and how does it benefit your network? | PC Gamer

Link-state routing protocols are one of the two main classes of routing protocols used in packet switching networks for computer communications, the other being distance-vector routing protocols. Examples of link-state routing protocols include Open Shortest Path First (OSPF) and Intermediate System to Intermediate System (IS-IS). The basic concept of link-state routing is that every node constructs a map of the connectivity to the network, in the form of a graph, showing which nodes are connected to which other nodes. Each node then independently calculates the next best logical path from it to every possible destination in the network. Each collection of best paths will then form each node’s routing table.

Two statements that are true about link-state routing protocols are:

The advertisement exchange is mainly triggered by a change in the network. Link-state routing protocols use a flooding mechanism to distribute information about the network topology to all routers in the same area or domain. This information is encapsulated in link-state packets (LSPs) or link-state advertisements (LSAs), which contain information about the router, its directly connected links, and the state of those links. LSPs or LSAs are sent only when there is a change in the topology, such as a link failure or recovery, or when a periodic refresh timer expires. This way, link-state routing protocols can quickly adapt to network changes and maintain an accurate and consistent view of the network.

Each router uses a reliable update mechanism to exchange topology information with its neighbors. Link-state routing protocols use a reliable update mechanism to ensure that all routers receive and acknowledge the LSPs or LSAs sent by their neighbors. This mechanism involves sending hello messages to establish and maintain adjacencies with neighbors, sending acknowledgment messages to confirm the receipt of LSPs or LSAs, and requesting missing or outdated LSPs or LSAs from neighbors. This mechanism ensures that all routers have a synchronized database of LSPs or LSAs, which is used to build a complete network connectivity map and to calculate the shortest path to destinations.

References: Link-state routing protocol - Wikipedia, Ericsson IP Networking - Routing Protocols