Free 4A0-114 Practice Test Questions and Answers (2026)

A BGP session being "stuck" in the Connect state means the local router has sent a TCP SYN packet to initiate a connection on port 179 but has not received a TCP SYN-ACK response from the remote peer. This indicates a failure in the TCP three-way handshake. The most likely cause is an issue on the remote peer or the path to it. This includes the remote peer not being configured with a matching neighbor statement, its BGP process not running, or a firewall/ACL blocking incoming TCP port 179 traffic.

A. A local misconfiguration (e.g., wrong peer IP) is possible, but issues on the remote side are a more common and direct cause for a lack of TCP response.
C. If BGP were administratively disabled locally, the router would not attempt to initiate a connection and would remain in the Idle state.
D. This is a specific instance of the correct answer (B). While true, option B is more comprehensive as it covers other remote issues like firewalls.

1. Y. Rekhter, T. Li, S. Hares, "RFC 4271: A Border Gateway Protocol 4 (BGP-4)," IETF, January 2006, Section 8.2.2.2, "Connect State". The description implies that the state persists while "waiting for the TCP connection to be completed," pointing to a lack of response from the peer.

2. Nokia, "7750 SR OS Router Configuration Guide," Release 22.10.R1, Part No: 3HE 18149 AAAD TQZZA, 2022, BGP Troubleshooting Section. This documentation typically correlates the Connect state with Layer 3/4 reachability problems, such as incorrect remote configuration, ACLs, or the remote BGP process being inactive.

In BGP-based transport tunnels, PE routers don't advertise their IP addresses as labeled BGP routes to identify tunnel endpoints. Instead, tunnel endpoints are identified through regular BGP NLRI (Network Layer Reachability Information) while labels are distributed for prefixes/services traversing the tunnel. The PE loopback addresses are typically distributed via IGP within regions and standard BGP between regions, not as labeled routes themselves.

A. MP-BGP label address families are essential for distributing MPLS labels via BGP for transport tunnels.
B. Inter-region MPLS tunnels are required to maintain label switching continuity across AS boundaries.
C. Intra-region MPLS tunnels are necessary for label switching within each autonomous system.

- Nokia Service Router Operating System (SR OS) Services Guide, Release 21.10.R1, Chapter: "BGP Transport Tunnels", Section 2.3.1

- RFC 8277 "Using BGP to Bind MPLS Labels to Address Prefixes", Section 3.1, October 2017

- Nokia 7750 SR Advanced Configuration Guide, "Multi-AS MPLS Networks", Pages 412-415

- IETF RFC 3107 "Carrying Label Information in BGP-4", Section 2, May 2001

- Nokia MPLS and Segment Routing Technical Guide, "Inter-AS Options", Chapter 4.2

In a BGP route reflector design, the CLUSTERLIST attribute is used to prevent routing loops. A route reflector (RR) and its clients form a cluster, identified by a CLUSTERID. When an RR reflects a route, it prepends its own CLUSTERID to the CLUSTERLIST. If an RR receives a route that already contains its own CLUSTERID in the CLUSTERLIST, it discards the route, thus preventing a loop. This mechanism is essential in topologies with multiple, redundant route reflectors.

A. MED is used to influence an external AS's routing decision on how to enter the local AS; it does not prevent intra-AS routing loops.
B. The ORIGIN attribute indicates the source of the route (e.g., IGP, EGP) and is a factor in path selection, not a loop prevention mechanism for route reflectors.
D. ASPATH is the primary loop prevention mechanism for eBGP (inter-AS), where a router rejects routes containing its own AS number. It does not solve iBGP looping issues introduced by route reflection.

1. Rekhter, Y., Li, T., & Hares, S. (2006). RFC 4271 - A Border Gateway Protocol 4 (BGP-4). IETF. Section 9.1, "Well-Known Mandatory Attributes," and Section 5.1.4, "CLUSTERLIST".

2. Bates, T., Chandra, R., Katz, D., & Rekhter, Y. (2006). RFC 4456 - BGP Route Reflection: An Alternative to Full Mesh Internal BGP (IBGP). IETF. Section 7, "Avoiding Routing Information Loops".

3. Nokia (2021). 7750 SR OS Router Configuration Guide, Release 21.10.R1. Document ID: 3HE 17279 AAAA TQZZA. BGP Route Reflection section.

A link-local address is automatically configured on every IPv6-enabled interface and is used only for on-link communication. All such addresses share the FE80::/10 prefix (not necessarily /64). The interface identifier is normally derived from the interface’s MAC (EUI-64) or generated pseudo-randomly; it is never generated from the interface’s IPv4 address. Therefore, option D is false.

A. RFC 4291 §2.5.6 mandates a link-local on every IPv6 interface.
B. Link-locals are not routed; scope is the local link.
C. All link-locals begin with FE80::/10, a common prefix.

1. RFC 4291, “IPv6 Addressing Architecture,” §2.5.6.

2. RFC 4862, “Stateless Address Autoconfiguration,” §5.3 (interface-ID formation).

3. Nokia IP Routing Protocols Guide, 21.10.R1, §2.3.1, pp. 47-48.

The Multi-Exit Discriminator (MED) is an optional, non-transitive BGP path attribute, as defined in RFC 4271. Its purpose is to influence how a neighboring Autonomous System (AS) chooses an entry point into the local AS. Because it is non-transitive, a BGP speaker that receives a MED value from a peer does not advertise that MED to other peers in different ASes. The statement that MED is transitive is therefore false. All other statements are true: MED is optional, a lower value is preferred, and it is set by an edge router to influence inbound traffic.

B: MED is classified as an optional attribute in BGP; it is not required in BGP UPDATE messages. C: The BGP decision process prefers the path with the lowest MED value when comparing routes received from the same neighboring AS. D: MED is set by an Autonomous System Border Router (ASBR) to indicate a preferred entry point to a neighboring AS.

1. RFC 4271, "A Border Gateway Protocol 4 (BGP-4)", Section 5.1.4, Page 21. States: "MULTIEXITDISC (Type Code 4): This is an optional, non-transitive attribute...".

2. Nokia 7750 SR OS BGP Protocol Guide, Release 22.10.R1, "BGP path attributes" section. Describes MED as an "optional non-transitive" attribute.

The BGP best-path selection algorithm evaluates attributes in a specific order. The very first attribute considered for routes from iBGP peers is LOCALPREF, where a higher value is preferred. The first route has a LOCALPREF of 150, while the other two have a LOCALPREF of 100. Therefore, the first route is unequivocally selected as the best path. By default, only the single best path for a prefix is installed in the routing table (RIB) and advertised to other BGP peers (placed in the RIB-out).

B. The second route has a lower local preference (100) than the first route (150) and will not be selected as the best path.
C. The third route also has a lower local preference (100) than the first route (150) and will not be selected as the best path.
D. BGP selects only one best path per prefix to install in the RIB and advertise by default; it does not forward all received routes.

1. Rekhter, Y., Li, T., & Hares, S. (2006). RFC 4271 - A Border Gateway Protocol 4 (BGP-4). IETF. Section 9.1.2, "LOCALPREF," and Section 9.1, "Decision Process".

2. Nokia (2021). 7750 SR OS Router Configuration Guide, Release 21.10.R1. Document ID: 3HE 17279 AAAA TQZZA. "BGP Path Selection" section.

3. Doyle, J., & Carroll, J. (2006). Routing TCP/IP, Volume II. Cisco Press. Chapter 5, "BGP Path Attributes and the BGP Decision Process".

EVPN is a versatile control plane that provides Layer 2 (VPLS-like) and Layer 3 (VPRN-like) connectivity using BGP. It uses a single BGP address family (AFI=25, SAFI=70) to advertise different route types for both L2 MAC addresses and L3 IP prefixes. EVPN is data plane agnostic, supporting encapsulations like MPLS and VXLAN. However, the term "backhaul VPLS" is a specific Nokia application referring to a VPLS service used for transport, often for mobile backhaul, and is not a standard term for a "local layer-2 EVPN service". A local EVPN service is simply an E-LAN or E-Line within a single site or data center.

A. This is the fundamental goal of EVPN: to provide flexible L2 and L3 VPN services over a common MPLS or IP network.
C. The EVPN BGP address family (L2VPN/EVPN) carries various route types, including MAC/IP routes (Type-2) for VPLS FDBs and IP Prefix routes (Type-5) for VPRN route tables.
D. EVPN is a control plane that is independent of the data plane encapsulation. It explicitly supports signaling for both MPLS and VXLAN tunnels.

1. Nokia 7750 SR OS Services Guide, Release 21.10.R1, "EVPN for VPLS services", Section: Introduction to EVPN. "Ethernet VPN (EVPN) is a BGP control plane solution for Ethernet services."

2. IETF RFC 7432, "BGP MPLS-Based Ethernet VPN", Section 1, Page 4. "This document specifies the procedures for BGP MPLS-based EVPNs."

3. IETF RFC 8365, "A Network Virtualization Overlay Solution Using Ethernet VPN (EVPN)", Section 1, Page 3. "This document describes a solution for network virtualization overlays (NVOs) using EVPN."

4. Nokia 7750 SR OS Services Guide, Release 21.10.R1, "VPLS", Section: Backhaul VPLS. This section describes backhaul VPLS as a specific application, distinct from the general definition of an EVPN service.

In a Nokia SR OS policy statement, when multiple match criteria of the same type (such as prefix-list) are configured within a single from clause, they are evaluated using a logical OR. The entry matches if the route's prefix is present in "List-1" OR "List-2". Since the action for this matching entry is reject, any BGP route that matches either of the prefix lists will be rejected by this import policy.

A. This is incorrect because the policy explicitly defines a reject action for routes matching the specified criteria.
B. This is incorrect because the logical operator between multiple prefix lists in a single from clause is OR, not AND.
D. This is incorrect for the same reason as option B; the evaluation logic is OR, meaning a route only needs to match one list to be rejected.

1. Nokia 7750 SR OS Router Configuration Guide, Release 21.10.R1, "Routing Policies". In the section "Policy Statement Entries", it is described that multiple match conditions of the same type in an entry are treated as a logical OR. (Document ID: 3HE 17279 AAAA TQZZA, Section: Policy Statement Entries)

The statement that eBGP peers have to be adjacent is false. While it is the default behavior and common configuration for eBGP peers to be directly connected (adjacent), it is not a strict requirement. BGP supports the ebgp-multihop feature, which allows eBGP sessions to be established between peers that are multiple IP hops away from each other. This is often used for peering between loopback interfaces for redundancy.

A. BGP relies on TCP for reliable transport. A TCP session can only be established if there is underlying IP connectivity between the peers.
B. iBGP peers are within the same AS and typically use an IGP for reachability, allowing them to be located anywhere within the AS, not necessarily adjacent.
D. This describes an external BGP (eBGP) session, which is the primary purpose of BGP: to exchange routing information between different Autonomous Systems.

1. Nokia (2021). Nokia SR OS BGP Configuration Guide. Section: "eBGP". The guide details the configuration of eBGP, including the multihop command to allow peering between non-adjacent routers.

2. Rekhter, Y., Li, T., & Hares, S. (2006). RFC 4271 - A Border Gateway Protocol 4 (BGP-4). Section 6.8, "EBGP and IBGP". The RFC notes the check for direct connection but implies it can be altered, which is the basis for the multihop feature.

The BGP Finite State Machine (FSM) defines the states a BGP session transitions through. When a TCP connection fails to be established, the session will typically be in either the Connect or Active state. In the Connect state, the router has initiated a TCP connection and is waiting for it to be completed. If this attempt fails (e.g., a timeout), the FSM transitions to the Active state, where the router listens for an incoming connection while periodically retrying to initiate a new one. The session will oscillate between these two states as long as TCP connectivity fails.

A. The Idle state is the initial state before any connection attempt is made. While the session starts there, it does not remain there during active failures.
B. While Active is a valid state for failure, the session must first pass through the Connect state, making the Connect/Active pair more descriptive.
D. The OpenSent state is reached only after a TCP connection has been successfully established, which contradicts the premise of the question.

1. Y. Rekhter, T. Li, S. Hares, "RFC 4271: A Border Gateway Protocol 4 (BGP-4)," IETF, January 2006, Section 8.2.2, "Finite State Machine". This section details the transitions: "If the TCP connection fails... the BGP speaker transitions to the Active state." and "In the Active state, the BGP speaker is trying to acquire a peer... If the ConnectRetryTimer expires... [it] transitions to the Connect state."

2. Nokia, "SR Linux BGP EVPN Cookbook," 2021, BGP Peering Section. The guide's troubleshooting examples show that TCP connectivity issues result in sessions flapping between Connect and Active states.