Review pre/post-NAT tuple, VIP rule, service selector, session log and backend listener. This check would diagnose Destination NAT and security-policy pair, but would not first isolate the described Loopback-based iBGP update source. Begin with: Inspect peer addresses, source interfaces, loopback routes and TCP endpoint addresses.

Check attached bits in LSPs, candidate L1/L2 routes and default forwarding behavior. This check would diagnose IS-IS L1 default to nearest attached L1L2, but would not first isolate the described Loopback-based iBGP update source. Begin with: Inspect peer addresses, source interfaces, loopback routes and TCP endpoint addresses.

Inspect adjacency graph, route source type and advertisement history on the transit router. This check would diagnose iBGP split-horizon route propagation, but would not first isolate the described Loopback-based iBGP update source. Begin with: Inspect peer addresses, source interfaces, loopback routes and TCP endpoint addresses.

Enable and verify the supported L2VPN EVPN MP-BGP address family for intended peers. This is a legitimate response to the different issue of MP-BGP address-family activation, but it does not correct the specific iBGP next-hop reachability condition reported. The relevant technical distinction is: BGP best-path and route installation require reachable NEXT_HOP; iBGP advertising does not always rewrite it.

Create a controlled BGP aggregate with valid components and safe discard or exception handling. This is a legitimate response to the different issue of BGP prefix aggregation and specifics, but it does not correct the specific iBGP next-hop reachability condition reported. The relevant technical distinction is: BGP best-path and route installation require reachable NEXT_HOP; iBGP advertising does not always rewrite it.

Set the Huawei ip ip-prefix network and greater-equal/less-equal bounds to the precise permitted prefixes. This is a legitimate response to the different issue of Prefix-list network and mask matching, but it does not correct the specific iBGP next-hop reachability condition reported. The relevant technical distinction is: BGP best-path and route installation require reachable NEXT_HOP; iBGP advertising does not always rewrite it.

Approved guest web traffic works while finance and management negative tests fail. That observation would support a separate case of Default-deny network segmentation, not verification of the reported iBGP next-hop reachability. The relevant observable outcome here is: Receiving iBGP routers resolve the BGP next hop and install the approved destination.

The peer sees the approved aggregate and every allocated component remains reachable under tested failures. That observation would support a separate case of BGP prefix aggregation and specifics, not verification of the reported iBGP next-hop reachability. The relevant observable outcome here is: Receiving iBGP routers resolve the BGP next hop and install the approved destination.

The loopback-sourced BGP session remains Established across the designated physical uplink change. That observation would support a separate case of Loopback-based iBGP update source, not verification of the reported iBGP next-hop reachability. The relevant observable outcome here is: Receiving iBGP routers resolve the BGP next hop and install the approved destination.

VRRP preemption controls whether a higher-priority returning router retakes the virtual gateway role. This explains VRRP preemption maintenance behavior, but not why the issue in this scenario occurs. The specific mechanism is: BGP best-path and route installation require reachable NEXT_HOP; iBGP advertising does not always rewrite it.

Higher BGP LOCAL_PREF is normally preferred within an AS and is not advertised to external AS peers. This explains BGP local preference internal egress, but not why the issue in this scenario occurs. The specific mechanism is: BGP best-path and route installation require reachable NEXT_HOP; iBGP advertising does not always rewrite it.

BGP OPEN negotiation validates the expected peer AS and session parameters. This explains BGP peer autonomous-system mismatch, but not why the issue in this scenario occurs. The specific mechanism is: BGP best-path and route installation require reachable NEXT_HOP; iBGP advertising does not always rewrite it.

Disabling AS loop detection to hide a policy error risks persistent routing loops. This consequence is associated more directly with BGP AS_PATH loop detection. For the stated conditions the immediate exposure is: An Established session with received prefixes can still leave routes unusable if next hops are unresolved.

Removing every nonforwarding link destroys the redundancy that spanning tree is designed to preserve. This consequence is associated more directly with RSTP alternate port failover. For the stated conditions the immediate exposure is: An Established session with received prefixes can still leave routes unusable if next hops are unresolved.

A permissive export filter can leak confidential topology and disrupt other routing domains. This consequence is associated more directly with BGP prefix export-filter leak. For the stated conditions the immediate exposure is: An Established session with received prefixes can still leave routes unusable if next hops are unresolved.

Inspect IGMP querier address, query intervals, group timers and receiver reports. This check would diagnose IGMP last-hop membership queries, but would not first isolate the described iBGP next-hop reachability. Begin with: Check BGP NEXT_HOP, recursive route resolution and underlay reachability on the receiver.

Inspect candidate origin codes, LOCAL_PREF, AS_PATH and decision order. This check would diagnose BGP origin attribute tie break, but would not first isolate the described iBGP next-hop reachability. Begin with: Check BGP NEXT_HOP, recursive route resolution and underlay reachability on the receiver.

Compare received candidate paths, LOCAL_PREF values, route policy and installed best path. This check would diagnose BGP local preference internal egress, but would not first isolate the described iBGP next-hop reachability. Begin with: Check BGP NEXT_HOP, recursive route resolution and underlay reachability on the receiver.

Bind the supported BGP session to the intended loopback update source and ensure transport reachability. This is a legitimate response to the different issue of Loopback-based iBGP update source, but it does not correct the specific iBGP next-hop reachability condition reported. The relevant technical distinction is: BGP best-path and route installation require reachable NEXT_HOP; iBGP advertising does not always rewrite it.

Use a supported consistent IS-IS metric style and cost plan across affected peers. This is a legitimate response to the different issue of IS-IS metric-style consistency, but it does not correct the specific iBGP next-hop reachability condition reported. The relevant technical distinction is: BGP best-path and route installation require reachable NEXT_HOP; iBGP advertising does not always rewrite it.

Configure the actual authorized remote AS consistently with the peer's BGP OPEN identity. This is a legitimate response to the different issue of BGP peer autonomous-system mismatch, but it does not correct the specific iBGP next-hop reachability condition reported. The relevant technical distinction is: BGP best-path and route installation require reachable NEXT_HOP; iBGP advertising does not always rewrite it.

The peer session reaches Established and eligible routes exchange under the agreed AS relationship. That observation would support a separate case of BGP peer autonomous-system mismatch, not verification of the reported iBGP next-hop reachability. The relevant observable outcome here is: Receiving iBGP routers resolve the BGP next hop and install the approved destination.

The chosen route matches the documented origin tie-break sequence and other path attributes. That observation would support a separate case of BGP origin attribute tie break, not verification of the reported iBGP next-hop reachability. The relevant observable outcome here is: Receiving iBGP routers resolve the BGP next hop and install the approved destination.

Internal BGP route decisions prefer the intended provider for matched prefixes and fail over if unavailable. That observation would support a separate case of BGP local preference internal egress, not verification of the reported iBGP next-hop reachability. The relevant observable outcome here is: Receiving iBGP routers resolve the BGP next hop and install the approved destination.

AS_PATH length is one BGP best-path criterion after important preceding preferences. This explains BGP AS_PATH length egress choice, but not why the issue in this scenario occurs. The specific mechanism is: BGP best-path and route installation require reachable NEXT_HOP; iBGP advertising does not always rewrite it.

RSTP selects a root bridge using bridge IDs and calculates loop-free port roles relative to that root. This explains RSTP root bridge location, but not why the issue in this scenario occurs. The specific mechanism is: BGP best-path and route installation require reachable NEXT_HOP; iBGP advertising does not always rewrite it.

QoS differentiation depends on packet classification, marking trust and congestion-aware queuing. This explains QoS DSCP remarking and trust, but not why the issue in this scenario occurs. The specific mechanism is: BGP best-path and route installation require reachable NEXT_HOP; iBGP advertising does not always rewrite it.

Confusing route types can leave inter-subnet overlay connectivity missing or misconfigured. This consequence is associated more directly with EVPN Type-2 MAC/IP route interpretation. For the stated conditions the immediate exposure is: An Established session with received prefixes can still leave routes unusable if next hops are unresolved.

Incorrect DIS assumptions can cause inconsistent troubleshooting and churn in shared-segment LSPs. This consequence is associated more directly with IS-IS DIS and pseudonode on broadcast LAN. For the stated conditions the immediate exposure is: An Established session with received prefixes can still leave routes unusable if next hops are unresolved.

Ignoring iBGP split horizon can silently prevent remote clients from learning routes. This consequence is associated more directly with iBGP split-horizon route propagation. For the stated conditions the immediate exposure is: An Established session with received prefixes can still leave routes unusable if next hops are unresolved.

Inspect rejected UPDATE attributes, local AS number and AS_PATH on each advertised prefix. This check would diagnose BGP AS_PATH loop detection, but would not first isolate the described iBGP next-hop reachability. Begin with: Check BGP NEXT_HOP, recursive route resolution and underlay reachability on the receiver.

Inspect candidate AS origins, MED values, higher-priority attributes and effective route-selection rules. This check would diagnose BGP MED same-neighbor-AS comparison, but would not first isolate the described iBGP next-hop reachability. Begin with: Check BGP NEXT_HOP, recursive route resolution and underlay reachability on the receiver.

Review ingress marks, traffic policy counters, queue occupancy and congestion test results. This check would diagnose QoS DSCP remarking and trust, but would not first isolate the described iBGP next-hop reachability. Begin with: Check BGP NEXT_HOP, recursive route resolution and underlay reachability on the receiver.