Ultimate Guide to Prepare ECP-206 Certification Exam for Ericsson Certified Associate in 2023 [Q26-Q41]

Explanation
To differentiate traffic types for the purpose of prioritization in their Ethernet LAN and IP/MPLS backbone, an operator can use the following three fields:
Traffic Class (TC): This is a 3-bit field in the MPLS label that can be used to indicate the priority or class of service (CoS) of the packet. The TC field can be mapped to the DSCP field in the IP header or the PCP field in the Ethernet header. The TC field can be used by MPLS routers to apply different per-hop behaviors (PHBs) such as queuing, scheduling, and dropping policies to different traffic classes12.
DSCP: This is a 6-bit field in the IP header that can be used to mark packets according to the differentiated services (DiffServ) model. The DSCP field can indicate the per-hop behavior (PHB) that the packet should receive at each router along its path. The DSCP field can be mapped to the TC field in the MPLS label or the PCP field in the Ethernet header. The DSCP field can be used by IP routers to provide QoS for different traffic types34.
PCP: This is a 3-bit field in the Ethernet header that can be used to mark packets according to the IEEE
802.1Q standard. The PCP field can indicate the priority or class of service (CoS) of the packet on an Ethernet LAN. The PCP field can be mapped to the TC field in the MPLS label or the DSCP field in the IP header. The PCP field can be used by Ethernet switches to provide QoS for different traffic types56.
References: MPLS Traffic Engineering – DiffServ-Aware Traffic Engineering, MPLS Traffic Engineering – DiffServ-Aware Traffic Engineering Configuration Guide, Differentiated services – Wikipedia, DSCP and Precedence Values – Cisco, 802.1Q VLAN IDs and Ethernet Interface Types – Juniper Networks, Introduction to Virtual LANs (VLANs) and Tagging – Ubiquiti Support and Help Center

Explanation
A P router is a provider router that is part of the service provider’s core network in an MPLS environment. A P router does not have any customer routes or VPN information, but only has information about how to reach other P routers and PE routers in the same MPLS domain. A P router performs label switching, which means that it forwards labeled packets based on their top label in the label stack. A P router can perform two possible label actions:
Swap: The P router replaces the incoming label with a new label that corresponds to the next hop along the label-switched path (LSP). The new label is determined by looking up the label forwarding information base (LFIB) based on the incoming label and interface.
PHP: The P router removes the top label from the packet at the penultimate hop before reaching the egress PE router. This is done to avoid an extra lookup on the egress PE router, which can forward the packet based on its IP header or another label in the stack.
A P router does not perform push or drop actions on labels. A push action means adding one or more labels to the packet, which is done by an ingress PE router when initiating an LSP. A drop action means discarding a packet, which is done by any router when there is no matching entry in its LFIB or routing table. References: Provider (P) Router in IP MPLS Network – Cisco Community, MPLS Fundamentals: Forwarding Labeled Packets – Cisco Press, MPLS Label Switching | MPLS Operation | Push, Swap,Push IPCisco

Explanation
Within an IGP area, routers advertise information about themselves and relay information delivered by neighbors. This is how link-state routing protocols such as OSPF and IS-IS work. They flood information about the network topology to all routers in the same area or domain. That information is then used to build a complete network connectivity map and to calculate the shortest path to destinations. Routers do not summarize or discard information within an area, unless they are configured to do so by some filtering mechanism. References: Ericsson IP Networking – Routing Protocols, IP Routing: ISIS Configuration Guide – IS-IS Overview and Basic Configuration

Explanation
An Ethernet switch will forward the frame to all ports when the destination address is FF:FF:FF:FF:FF:FF.
This is because this address is the broadcast MAC address, which means that the frame is intended for all devices on the same LAN segment. The switch does not need to look up its MAC address table to find a matching entry for this address, but simply floods the frame out of all ports except the one where it received the frame. This way, the frame reaches every device on the LAN segment, regardless of their MAC addresses. References: Ethernet – Wireshark, Broadcast MAC Address – omnisecu.com

Explanation
Priority queuing (PQ) is a queuing method that establishes four interface output queues that serve different priority levels: high, medium, normal, and low. Traffic in the highest priority queue will experience the least amount of jitter and delay compared to traffic in the other queues, because PQ always services the higher-priority queues first. However, this can also cause traffic in lower priority queues to be starved of bandwidth, especially if the highest priority queue is oversubscribed. Traffic in the highest priority queue is not only reserved for voice traffic, but can also include network control and routing traffic. Traffic in all queues are not always guaranteed a minimum bandwidth, because PQ does not provide any bandwidth reservation mechanism. References: Quality of Service (QoS) Queues and Queuing Explained, Chapter:
Configuring Priority Queueing – Cisco

Explanation
The operating system used in Ericsson Router 6000 products is ERS (Ericsson Router Software). ERS is based on IPOS (IP Operating System), which is a common operating system for Ericsson’s IP portfolio. ERS provides advanced features and functionality for IP transport, such as MPLS, Segment Routing, QoS, IPSec, synchronization, SDN, and more. ERS also supports seamless integration with Ericsson Radio System and Ericsson Network Manager.
References: Router 6000 Series – Ericsson, Router 6675 Datasheet – Winncom

Explanation
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

Explanation
MTU mismatch would cause an IS-IS adjacency between two routers to fail. MTU stands for maximum transmission unit, which is the maximum size of a packet that can be transmitted on a link. IS-IS hellos are padded to the full MTU size, partly to allow a router to implicitly communicate its MTU to its neighbors. If two routers have different MTUs on their interfaces, they will not be able to exchange hellos properly, and their adjacency will not form or will be dropped34. To solve this problem, the MTUs on both interfaces must be configured to match.
SEL, context, and SysID are not fields that would cause an IS-IS adjacency failure. SEL stands for selector, which is a one-octet field that identifies the network layer service to which a packet should be sent. For IS-IS routers, the SEL must always be 005. Context is not a field in IS-IS packets, but rather a term used to describe the scope of routing information in different levels or areas6. SysID stands for system identifier, which is a six-octet field that uniquely identifies a router within an area. SysID does not have to match between two routers for them to form an adjacency7.
References: MTU Mismatch Problem in IS-IS – Cisco, IS-IS adjacency is not formed due to MTU mismatch – Cisco Community, IS-IS NSAP address – Cisco Community, Understanding IS-IS Routing Contexts – Juniper Networks, IS-IS – Nokia

Explanation
For IP destinations not found in the IS-IS Level 1 database, the Level 1 router must forward packets to the nearest Level 1-Level 2 router with the attach bit set. The attach bit is a flag in the IS-IS Level 1 LSP that indicates that the router is also a Level 2 router and can reach destinations outside the Level 1 area. The Level
1 router will install a default route pointing to the nearest Level 1-Level 2 router with the attach bit set. This way, the Level 1 router can forward packets to other areas without having to maintain a full Level 2 database. References: Ericsson IP Networking – Routing Protocols, Configure Attach Bit Set – Cisco

Explanation
The Area ID to which the router belongs is 49.00F0.0100. The Area ID is a variable-length field in the NSAP address that identifies the area to which the router belongs. The Area ID can be between 1 and 13 bytes long, but it must start and end with an octet (8 bits). The NSAP address is composed of three parts: the authority and format identifier (AFI), the area ID, and the system ID. The AFI is a one-octet field that indicates the format and authority of the rest of the address. The system ID is a fixed-length field of six octets that uniquely identifies the router within an area. The NSAP address also has a network selector (NSEL) field, which is a one-octet field that identifies the network layer service to which a packet should be sent. For IS-IS routers, the NSEL must always be 00.
In this question, the NSAP address is 49.00F0.0100.5012.3010.00. This means that:
The AFI is 49, which indicates a private address.
The Area ID is 00F0.0100, which is four octets long and starts and ends with an octet.
The system ID is 5012.3010, which is six octets long and identifies the router within the area.
The NSEL is 00, which indicates IS-IS.
Therefore, the answer is B.
References: Ericsson IP Networking – Routing Protocols, IS-IS NSAP address – Cisco Community, Understanding IS-IS NSAP Addresses – Todd Lammle, LLC, IS-IS – Nokia, Network service access point address – Wikipedia

Explanation
Route summarization is a technique that reduces the number of routes that a router advertises to its neighbors by creating a single summary route that covers multiple subnets or networks. Route summarization has several benefits, such as:
It reduces the size of a routing table, which saves memory and CPU resources on the router. A smaller routing table also improves the lookup efficiency and convergence time of the routing protocol.
It reduces signaling, which means that less bandwidth is consumed by routing updates and less processing is required by neighboring routers. This also enhances the stability and scalability of the network, as fewer routing changes are propagated.
It improves route aggregation, which means that more specific routes are replaced by a less specific route that can be advertised to other autonomous systems or routing domains. This simplifies the inter-domain routing and hides the internal topology details.
Route summarization does not necessarily summarize the routing table entries into a default route, although a default route can be considered a special case of route summarization where all destinations are covered by one route. Route summarization also does not improve the best route calculation, as it may introduce suboptimal routing or black holes if not done properly. : Introduction to Route Summarization – NetworkLessons.com, Route Summarization > Example for Understanding Route Summarization – Cisco Press

Explanation
IPv6 link-local addresses are designed to be used in three situations: for neighbor discovery, for local IP communication on the IPv6 capable routers, and for addressing on a single link for purposes such as auto-address configuration. Neighbor discovery is a protocol that allows IPv6 nodes to discover each other and learn their link-layer addresses on a local network. Neighbor discovery uses link-local addresses to send and receive messages such as router advertisements, router solicitations, neighbor advertisements, and neighbor solicitations34. Local IP communication on the IPv6 capable routers refers to the ability of routers to exchange routing information or management traffic using their link-local addresses as source and destination addresses. This reduces the need for global unicast addresses on router interfaces that are not reachable from outside the local network35. Addressing on a single link for purposes such as auto-address configuration refers to the use of link-local addresses to enable IPv6 nodes to obtain an address without manual configuration or a DHCP server. Link-local addresses can be automatically derived from the interface identifier in the modified EUI-64 format or randomly generated. Link-local addresses can also be used to test the connectivity of a link before obtaining a global unicast address36.
References: Understand the IPv6 Link-Local Address – Cisco, Link Local Address – GeeksforGeeks, IPv6 Address Types | Link-Local, Global Unicast, etc. IPCisco, MPLS Label Distribution Protocol Commands – Cisco

Explanation
The statement that accurately defines an Autonomous System (AS) is that an AS is a set of routers under a single administration, using an interior gateway protocol and common metrics to route packets within the AS.
An AS is a logical grouping of networks that share a common routing policy and operate under a single administrative authority. An AS can be a single network or a collection of networks that are interconnected by routers. An AS uses an interior gateway protocol (IGP), such as OSPF or IS-IS, to exchange routing information within the AS. An IGP uses common metrics, such as hop count or bandwidth, to determine the best path to each destination within the AS. An AS also has a unique number assigned by IANA, called an AS number (ASN), which identifies the AS in interdomain routing .
References: [Autonomous system (Internet) – Wikipedia], [What Is an Autonomous System? – Cisco]

Explanation
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

Explanation
The router function that advertises external routes in OSPF is ASBR, which stands for Autonomous System Boundary Router. An ASBR is a router that connects an OSPF domain to another routing domain, such as another OSPF domain or a different routing protocol domain. An ASBR can redistribute routes from other routing domains into OSPF as external routes, which are carried in type 5 or type 7 LSAs. External routes have two types: E1 and E2. E1 routes include the cost from the ASBR to the destination, while E2 routes only include the cost advertised by the ASBR34.
References: OSPF External Routes IpCisco, OSPF External Route selection algorithm – Cisco Community

Explanation
Referring to the exhibit, the two Ericsson routers that support the 100GE interface are Router 6675 and Router
6672. The 100GE interface is a high-speed Ethernet interface that operates at 100 gigabits per second. The Ericsson Router 6000 series is a family ofrouters that provide IP transport for mobile and fixed networks. The Router 6675 is a 5G combined access and E-RAN switch with 100GE interfaces and 320Gb forwarding capacity. The Router 6672 is a high-capacity metro aggregation router with 100GE interfaces and 1.6Tb forwarding capacity12.
References: Router 6000 Series – Ericsson, New Ericsson Router 6000 series couples radio and IP transport for
5G future – Global Brands Magazine