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This option proposes: The IS-IS designated intermediate system generates pseudonode LSP information for a broadcast LAN, and IS-IS does not create an OSPF-style backup designated intermediate system for the same segment. It addresses the different topic IS-IS designated intermediate system and pseudonode, not the directly tested IS-IS routing leakage and overload bit failure in the stated incident (A regional L1/L2 router learns a branch prefix but another area does not; the team needs to identify whether configured interlevel route leaking is missing.).

This option proposes: VRRP uses a virtual router identity and virtual MAC per IPv4 group to preserve a stable next-hop identity across master changes; correct failover still requires matching VLAN, neighbor learning and eligible router state. It addresses the different topic VRRP virtual MAC and endpoint ARP continuity, not the directly tested IS-IS routing leakage and overload bit failure in the stated incident (A regional L1/L2 router learns a branch prefix but another area does not; the team needs to identify whether configured interlevel route leaking is missing.).

This option proposes: IS-IS floods LSPs and uses Complete Sequence Number PDUs and Partial Sequence Number PDUs to summarize holdings, request missing LSPs and acknowledge entries depending on circuit behavior. It addresses the different topic IS-IS LSP synchronization using CSNP and PSNP, not the directly tested IS-IS routing leakage and overload bit failure in the stated incident (A regional L1/L2 router learns a branch prefix but another area does not; the team needs to identify whether configured interlevel route leaking is missing.).

This option proposes: Inspect LAN IIH priorities, elected DIS system ID, pseudonode LSPs and neighbor topology before changing interface priority. It addresses the different topic IS-IS designated intermediate system and pseudonode, not the directly tested IS-IS routing leakage and overload bit failure in the stated incident (A regional L1/L2 router learns a branch prefix but another area does not; the team needs to identify whether configured interlevel route leaking is missing.).

This option proposes: Inspect source and destination zones, policy match, existing session, NAT translation and deny logs for the tested client flow. It addresses the different topic Stateful firewall sessions versus basic packet ACL filtering, not the directly tested IS-IS routing leakage and overload bit failure in the stated incident (A regional L1/L2 router learns a branch prefix but another area does not; the team needs to identify whether configured interlevel route leaking is missing.).

This option proposes: Compare LSP identifiers, sequence numbers, aging, CSNP summaries, PSNP entries and adjacency state on the affected circuit. It addresses the different topic IS-IS LSP synchronization using CSNP and PSNP, not the directly tested IS-IS routing leakage and overload bit failure in the stated incident (A regional L1/L2 router learns a branch prefix but another area does not; the team needs to identify whether configured interlevel route leaking is missing.).

That option concerns IS-IS designated intermediate system and pseudonode. That follows from the targeted Recommended action: Check IS-IS level-1-to-level-2 route leaking and the overload bit before selecting a device as a transit path.

That option concerns IS-IS LSP synchronization using CSNP and PSNP. That follows from the targeted Recommended action: Check IS-IS level-1-to-level-2 route leaking and the overload bit before selecting a device as a transit path.

That option concerns OSPF router network and summary LSA scope. That follows from the targeted Recommended action: Check IS-IS level-1-to-level-2 route leaking and the overload bit before selecting a device as a transit path.

This option proposes: Analyze Virtual Router Redundancy Protocol master election using priorities and the virtual router ID instead of a router's physical interface address alone. It addresses the different topic VRRP master election priority and tie breaks, not the directly tested BGP transport reachability and session states failure in the stated incident (Two edge routers are configured as external BGP neighbors but the session oscillates between Connect and Active after an ACL blocks TCP port 179.).

This option proposes: Investigate a BGP route that appears in a peer table but fails to install because its NEXT_HOP is unresolved. It addresses the different topic BGP NEXT_HOP reachability and next-hop-self, not the directly tested BGP transport reachability and session states failure in the stated incident (Two edge routers are configured as external BGP neighbors but the session oscillates between Connect and Active after an ACL blocks TCP port 179.).

This option proposes: Apply route-reflector client roles and loop-prevention attributes to an iBGP topology that must scale beyond a full mesh. It addresses the different topic BGP route reflector and cluster loop prevention, not the directly tested BGP transport reachability and session states failure in the stated incident (Two edge routers are configured as external BGP neighbors but the session oscillates between Connect and Active after an ACL blocks TCP port 179.).

This option proposes: MED is an optional nontransitive BGP attribute, with lower values typically favored when compared under applicable rules; it is often compared for routes from the same neighboring AS unless policy changes this behavior. It addresses the different topic BGP MED interpretation between neighboring autonomous systems, not the directly tested BGP transport reachability and session states failure in the stated incident (Two edge routers are configured as external BGP neighbors but the session oscillates between Connect and Active after an ACL blocks TCP port 179.).

This option proposes: PIM-DM generally follows a flood-and-prune model, building source-based multicast distribution where an interface without interested downstream receivers can be pruned to reduce unnecessary traffic. It addresses the different topic PIM dense mode flooding and prune mechanisms, not the directly tested BGP transport reachability and session states failure in the stated incident (Two edge routers are configured as external BGP neighbors but the session oscillates between Connect and Active after an ACL blocks TCP port 179.).

This option proposes: A BGP network statement generally requires an appropriate matching route in the local routing table, whereas importing routes from other protocols uses an explicit redistribution mechanism; export policy can further restrict announcements. It addresses the different topic BGP route origin network and redistribution policy, not the directly tested BGP transport reachability and session states failure in the stated incident (Two edge routers are configured as external BGP neighbors but the session oscillates between Connect and Active after an ACL blocks TCP port 179.).

This option proposes: Inspect member and master status, stack-link connectivity, dual-active detection mechanisms and forwarding after an isolated partition test. It addresses the different topic Switch stacking clustering and split-brain risk, not the directly tested BGP transport reachability and session states failure in the stated incident (Two edge routers are configured as external BGP neighbors but the session oscillates between Connect and Active after an ACL blocks TCP port 179.).

This option proposes: Inspect the community attached to a prefix, the matching community filter, permit or deny clauses and the route after policy application. It addresses the different topic BGP community tagging and route-policy control, not the directly tested BGP transport reachability and session states failure in the stated incident (Two edge routers are configured as external BGP neighbors but the session oscillates between Connect and Active after an ACL blocks TCP port 179.).

This option proposes: Inspect the received AS_PATH, origin AS, eBGP neighbor AS, policy additions and route-selection evidence before changing prepend counts. It addresses the different topic BGP AS_PATH path-vector loop prevention, not the directly tested BGP transport reachability and session states failure in the stated incident (Two edge routers are configured as external BGP neighbors but the session oscillates between Connect and Active after an ACL blocks TCP port 179.). The better discriminating check for this case is: Compare peer state transitions, source addresses, route to the peer, TCP 179 connectivity, local/remote AS settings and notification codes. The targeted correction is: Troubleshoot BGP establishment by distinguishing TCP port 179 transport, peer configuration and OPEN capability negotiation.

That option concerns PIM sparse mode RP shared tree and shortest path transition. That follows from the targeted action: Troubleshoot BGP establishment by distinguishing TCP port 179 transport, peer configuration and OPEN capability negotiation.

That option concerns MP-BGP EVPN route types and forwarding separation. That follows from the targeted action: Troubleshoot BGP establishment by distinguishing TCP port 179 transport, peer configuration and OPEN capability negotiation.

That option concerns BGP route origin network and redistribution policy. That follows from the targeted action: Troubleshoot BGP establishment by distinguishing TCP port 179 transport, peer configuration and OPEN capability negotiation.

This option proposes: Treat a BGP route shown as received as sufficient evidence of packet forwarding when the NEXT_HOP has no route in the receiving router. It addresses the different topic BGP NEXT_HOP reachability and next-hop-self, not the directly tested BGP transport reachability and session states failure in the stated incident (Two edge routers are configured as external BGP neighbors but the session oscillates between Connect and Active after an ACL blocks TCP port 179.).

This option proposes: Enable OSPF neighbor formation on an untrusted user access VLAN because route advertisement is presumed impossible without forming user-device adjacencies. It addresses the different topic OSPF interface security and passive network advertisement, not the directly tested BGP transport reachability and session states failure in the stated incident (Two edge routers are configured as external BGP neighbors but the session oscillates between Connect and Active after an ACL blocks TCP port 179.).

This option proposes: Assume any iBGP speaker automatically reflects routes learned from one iBGP peer to every other iBGP neighbor without reflector configuration. It addresses the different topic BGP route reflector and cluster loop prevention, not the directly tested BGP transport reachability and session states failure in the stated incident (Two edge routers are configured as external BGP neighbors but the session oscillates between Connect and Active after an ACL blocks TCP port 179.).

That option concerns IPv6 SLAAC RA prefix and duplicate address detection. Confirm it using: Compare peer state transitions, source addresses, route to the peer, TCP 179 connectivity, local/remote AS settings and notification codes.

That option would inspect the received AS_PATH, origin AS, eBGP neighbor AS, policy additions and route-selection evidence before changing prepend counts, but it addresses a different concern. Confirm it using: Compare peer state transitions, source addresses, route to the peer, TCP 179 connectivity, local/remote AS settings and notification codes.

That option concerns IPsec VPN IKE negotiation versus ESP data channel. Confirm it using: Compare peer state transitions, source addresses, route to the peer, TCP 179 connectivity, local/remote AS settings and notification codes.

This option proposes: Distinguish EVPN control-plane route information and underlay forwarding when analyzing a VXLAN-enabled fabric. It addresses the different topic MP-BGP EVPN route types and forwarding separation, not the directly tested BGP transport reachability and session states failure in the stated incident (A newly created iBGP peer uses a loopback source yet the opposite router has no route to that loopback and the session never forms.).

This option proposes: Diagnose outbound path choice across iBGP speakers using locally distributed LOCAL_PREF values. It addresses the different topic BGP LOCAL_PREF within one autonomous system, not the directly tested BGP transport reachability and session states failure in the stated incident (A newly created iBGP peer uses a loopback source yet the opposite router has no route to that loopback and the session never forms.).

This option proposes: Configure VRRP priority tracking with suitable preemption behavior so loss of upstream connectivity changes the preferred gateway. It addresses the different topic VRRP interface tracking and controlled preemption, not the directly tested BGP transport reachability and session states failure in the stated incident (A newly created iBGP peer uses a loopback source yet the opposite router has no route to that loopback and the session never forms.).

This option proposes: A BGP network statement generally requires an appropriate matching route in the local routing table, whereas importing routes from other protocols uses an explicit redistribution mechanism; export policy can further restrict announcements. It addresses the different topic BGP route origin network and redistribution policy, not the directly tested BGP transport reachability and session states failure in the stated incident (A newly created iBGP peer uses a loopback source yet the opposite router has no route to that loopback and the session never forms.).

This option proposes: IS-IS LSP control flags and route-leaking policy determine appropriate reachability; an overload indication can steer other routers away from using an overloaded node as transit while preserving selected directly attached reachability. It addresses the different topic IS-IS routing leakage and overload bit, not the directly tested BGP transport reachability and session states failure in the stated incident (A newly created iBGP peer uses a loopback source yet the opposite router has no route to that loopback and the session never forms.).

This option proposes: BGP AS_PATH records traversed autonomous systems, and an eBGP router ordinarily rejects a received route containing its own AS; prepending the local AS can influence some external path decisions but does not override every selection policy. It addresses the different topic BGP AS_PATH path-vector loop prevention, not the directly tested BGP transport reachability and session states failure in the stated incident (A newly created iBGP peer uses a loopback source yet the opposite router has no route to that loopback and the session never forms.).