初心者向けのECP-206試験 [2023] 問題集でEricssonのPDF問題 [Q26-Q47]

Explanation
Referring to the exhibit, the correct statement is that the service provider’s P routers are not aware of the customers’ routes. This is because P routers only need to forward MPLS packets based on their labels, without looking into their IP headers or VPN information. The P routers do not have any VRFs configured for the customers, nor do they participate in MP-BGP sessions with other PE routers. The PE routers are responsible for maintaining VRFs for each customer and for exchanging VPN routes with other PE routers using MP-BGP910.
References: Layer 3 VPNs (L3VPN) – Cisco, MPLS VPN – Wikipedia

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 maximum number of unique VLAN IDs available is 4096. A VLAN ID is a 12-bit identifier that can range from 0 to 4095. However, VLAN ID 0 is reserved for tagging the priority of frames and VLAN ID 4095 is reserved for implementation use, so only VLAN IDs from 1 to 4094 are available for user configuration78.
VLAN IDs are used to identify different broadcast domains or subnets on a Layer 2 network. VLAN IDs are carried in the IEEE 802.1Q tag in the Ethernet frame header.
References: What is a virtual LAN (VLAN) and how does it work with my managed switch? – NETGEAR Support, Virtual LANs (VLANs) – Cisco

Explanation
IPsec provides two main features: protecting packets from modification and hiding the content of packets from observation. IPsec protects packets from modification by using cryptographic algorithms to generate and verify message authentication codes (MACs) or digital signatures for each packet. These mechanisms ensure that the packets have not been tampered with or altered in transit by unauthorized parties. IPsec hides the content of packets from observation by using encryption algorithms to scramble the payload of each packet. This prevents eavesdroppers or interceptors from reading or analyzing the data carried by the packets12.
References: What is IPsec? | How IPsec VPNs work | Cloudflare, IPsec – Wikipedia

Explanation
A label-edged router (LER) is a PE router. A PE router is a provider edge router, which is a router that connects an MPLS network to a customer network. A LER is a term used in MPLS to describe a router that resides at the ingress and egress points of an MPLS network, handling both labelled and unlabelled packets. A LER performs label operations such as adding, removing, or swapping labels on packets entering or leaving the MPLS network34.
References: What is Label Edge Router (LER)? – Definition from Techopedia, LER – Label Edge Router – Mpirical

Explanation
An LDP implicit null label causes penultimate hop popping by a downstream router. LDP is a protocol that distributes labels for MPLS forwarding along the shortest path calculated by an IGP. An implicit null label is a special label value of 3 that indicates that the downstream router does not need a label to forward the packet to its destination. When an upstream router receives an implicit null label from a downstream router, it removes (or pops) the label from the packet before sending it to the downstream router. This process is called penultimate hop popping (PHP) and it reduces the load on the downstream router, which can forward the packet based on its IP header or another label in the stack59.
References: MPLS Label Distribution Protocol Commands – Cisco, Solved: Implicit null and Explicit null – 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

Explanation
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

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
A network operator who wants to make sure voice data is prioritized should assign it to Ethernet traffic class 6.
Ethernet traffic class is a term used to refer to the priority code point (PCP) field in the VLAN header of an Ethernet frame. The PCP field is a 3-bit field that can encode up to eight different priority levels, ranging from
0 (lowest) to 7 (highest). The PCP values can be mapped to different types of traffic according to their QoS requirements. The recommended mapping is as follows :
PCP 0: Best effort (default)
PCP 1: Background
PCP 2: Spare
PCP 3: Excellent effort
PCP 4: Controlled load
PCP 5: Video
PCP 6: Voice
PCP 7: Network control
Voice data is a type of real-time traffic that requires the highest priority and lowest delay in the network.
Therefore, it should be assigned to PCP 6, which corresponds to Ethernet traffic class 6 .
References: [IEEE 802.1Q – Wikipedia], [What is “link aggregation” and how does it benefit your network? | PC Gamer]

Explanation
Two statements that are true about router node hardening are:
Any unnecessary services should be disabled within each context. Router node hardening is a process of securing a router from unauthorized access and attacks by applying various configurations and policies.
One of these configurations is to disable any services that are not needed for the router’s functionality or purpose, such as telnet, ftp, http, etc. This reduces the attack surface of the router and prevents potential exploits of these services91.
Enabling syslog ensures system events are logged to a remote server. Syslog is a protocol that allows a router to send system messages and events to a remote server for logging and analysis. By enabling syslog on a router, network administrators can monitor the router’s activity and performance, troubleshoot problems, detect anomalies, and audit security events101.
References: Cisco Router Hardening Step-by-Step | SANS Institute, Security Hardening Checklist Guide for Cisco Routers/Switches in 10 Steps, CCNA SEC: Router Hardening – Cisco Press

Explanation
iBGP works by exchanging routing information between two or more routers within an AS. Each router sends its own routing table to its neighbors, which contains information about the networks it knows and how they can be reached from that router. By default, iBGP neighbors only share BGP routes learned from eBGP neighbors, which are routers in different ASes. This is because iBGP assumes that all routers within an AS have consistent internal routing information provided by an IGP, such as OSPF or IS-IS. Therefore, iBGP neighbors do not need to share IP address information of loopbackinterfaces or directly connected interfaces, unless explicitly configured to do so by using commands such as neighbor update-source or network.
References: iBGP Ultimate Guide | How iBGP Is Different From eBGP, Ericsson IP Networking – Routing Protocols

Explanation
The CLI command to obtain the software version in Ericsson Router 6000 products is show version. This command displays information about the software release, the hardware model, the serial number, the uptime, and the boot image of the router. References: [ERICSSON SMARTEDGE 600 HARDWARE MANUAL Pdf Download | ManualsLib], Ericsson Router 6000 Series – Ericsson

Explanation
Spanning-Tree is used for Ethernet loop avoidance. Spanning-Tree is a protocol that prevents loops in Ethernet networks by creating a logical tree topology of the network switches. Spanning-Tree blocks some of the redundant links between switches to ensure that there is only one active path between any two nodes in thenetwork. Spanning-Tree also detects and recovers from link failures by activating alternative paths when needed56.
References: Network loops and loop avoidance – Medium, Spanning Tree Protocol – Wikipedia

Explanation
P routers forward packets based on the LSP label. The LSP label is the label that corresponds to the label-switched path (LSP) that is established between two PE routers in an MPLS network. The LSP label is also called the outer label or the transport label, because it is used to transport packets across the MPLS core network. P routers are also called LSRs (label switch routers) or transit routers, because they switch packets based on their labels or remove the labels. P routers do not need to look at the IP header or any other information in the packet, except for the top label in the label stack. P routers perform one of three possible operations on labels: swap, pop, or PHP (penultimate hop popping). In a swap operation, the label is swapped with a new label, and the packet is forwarded along the path associated with the new label. In a pop operation, the label is removed from the packet, and the packet is forwarded based on its IP header or another label in the stack. In a PHP operation, the label is removed from the packet at the last P router before reaching the egress PE router, and the packet is forwarded without any label to the egress PE router.
The LSP label is different from other types of labels that may be used in MPLS networks, such as VPN labels or service labels. These labels are used to identify different VPNs or services that run over MPLS networks, such as Layer 2 VPNs, Layer 3 VPNs, traffic engineering, or QoS. These labels are also called inner labels or payload labels, because they are related to the payload of the packet. These labels are not used by P routers for forwarding decisions, but only by PE routers for delivering packets to their destinations.
Therefore, the answer is C.
References: Ericsson IP Networking – Routing Protocols, MPLS Fundamentals: Forwarding Labeled Packets – Cisco Press, MPLS Labels and Devices – NetworkLessons.com, Multiprotocol Label Switching – Wikipedia, VPN Packet Forwarding > MPLS/VPN Architecture Overview | Cisco Press, Basic concepts – Hewlett Packard Enterprise

Explanation
LDP relies on IGP for all routing-related decisions. LDP is a protocol that distributes labels in an MPLS environment, but it does not perform any routing functions. LDP uses the underlying routing information provided by an IGP, such as OSPF or IS-IS, to forward label packets. LDP and IGP do not exchange their databases at regular intervals, but rather use hello messages to maintain adjacencies and sessions. References: Ericsson IP Networking – Routing Protocols, Label Distribution Protocol – Wikipedia

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
The next-hop to reach the host 192.168.1.129 is 10.126.131.250. This can be determined by looking at the routing table in the exhibit. The host 192.168.1.129 falls within the range of the network 192.168.1.64/26, which has a next-hop of 10.126.131.250. References: Ericsson IP Networking – IP Addressing, Software Installation and Upgrade Overview (Junos OS)

Explanation
The correct abbreviation for the IP address BFEA:DACA:0000:0000:9390:0000:0000:D91 is BFEA:DACA::9390:0:D91. IPv6 addresses are represented in hexadecimal notation, with eight 16-bit segments separated by colons. To simplify the address representation, IPv6 supports two types of abbreviations. The first abbreviation allows us to skip leading zeros within a segment, while the second abbreviation allows us to drop one or more consecutive segments that contain only zeros, using a double colon (::) instead. However, the double colon can be used only once in an address, to avoid ambiguity34.
References: IPv6 Address Types, Notation, and Structure Explained, IPv6 address – Wikipedia

Explanation
A BGP session is established between two routers by sending a unicast OPEN message. BGP uses TCP as its transport protocol, which means that before exchanging any BGP information, a TCP connection must be established between the routers. The TCP connection uses port 179 as both source and destination port. After establishing a TCP connection, each router sends an OPEN message to its neighbor, containing parameters such as BGP version number, AS number, hold time, BGP identifier, and optional capabilities. The OPEN message also serves as a keepalive message for BGP. If both routers agree on these parameters, they proceed to exchange UPDATE messages containing routing information and establish a BGP session.
A BGP router does not send a NOTIFICATION message to establish a session, but rather to terminate a session due to an error or a manual shutdown. A BGP router does not send a CONNECT message, as this is a TCP state, not a BGP message. A BGP router does not send a multicast HELLO packet, as this is an OSPF message, not a BGP message. References: BGP Neighbor States > BGP Fundamentals | Cisco Press, Demystifying BGP Session Establishments – Packet Pushers, The TCP/IP Guide – BGP Connection Establishment: Open Messages

Explanation
According to RFC1918, there are three network blocks reserved as private networks that are not allocated to any specific organization and are not routable on the public Internet. These are:
10.0.0.0/8 (10.0.0.0 – 10.255.255.255)
172.16.0.0/12 (172.16.0.0 – 172.31.255.255)
192.168.0.0/16 (192.168.0.0 – 192.168.255.255)
Out of these, only option B (10.254.1.0/24) falls within one of the private network blocks (10.0.0.0/8). Option A (172.16.1.0/9) is not valid because it exceeds the /12 prefix length of the private network block (172.16.0.0/12). Option C (193.168.1.0/24) is not valid because it does not belong to any of the private network blocks, and is actually assigned to RIPE NCC as a public network block . Option D (172.15.1.0/24) is also not valid because it does not belong to any of the private network blocks, and is actually assigned to ARIN as a public network block . References: RFC 1918: Address Allocation for Private Internets, Private network – Wikipedia, [RIPE NCC IPv4 Address Space Chart], [ARIN WHOIS Database Search]

Explanation
In an Ethernet frame carrying a VLAN tag, the VLAN tag appears before the type field. A VLAN tag is a
4-byte field that is inserted into an Ethernet frame to indicate the VLAN membership and priority of the frame.
The VLAN tag consists of two subfields: the tag protocol identifier (TPID) and the tag control information (TCI). The TPID subfield is a 16-bit field that identifies the frame as an IEEE 802.1Q-tagged frame, with a value of 0x8100. The TCI subfield is a 16-bit field that contains the priority code point (PCP), the drop eligible indicator (DEI), and the VLAN identifier (VID). The VLAN tag appears between the source MAC address and the type fields of the original frame, shifting the type field by four bytes. The type field indicates the type of the payload, such as IP or ARP .
References: [IEEE 802.1Q – Wikipedia], [VLAN Tagging Explained with DTP Protocol – GeeksforGeeks]