When an LSP ping succeeds but the trace shows a loop, it often indicates a forwarding plane issue where the data plane and control plane are out of sync. A common cause is a ‘forwarding adjacency mismatch’ in the IGP, where nodes have inconsistent views of the network topology or metrics for the LSP’s path. This causes the MPLS label to be swapped to a next-hop that then sends it back, creating a loop. While RSVP issues could cause setup failure, the success of the ping indicates the LSP is established. Static route misconfiguration is less likely for a signaled LSP, and load-balancing would cause out-of-order packets, not a consistent loop in a trace.

The Nokia ‘Mobile Transport Solution for 5G xHaul’ is a comprehensive portfolio that includes routers (like the 7250 Interconnect Router) and WDM/OTN platforms specifically optimized for the capacity, latency, and synchronization (e.g., IEEE 1588v2, SyncE) requirements of 5G fronthaul, midhaul, and backhaul. While the 7750 SR can be used in backhaul and NSP provides management, the xHaul solution is the end-to-end architecture designed for this purpose. WaveSuite addresses WDM but not the full packet transport needs.

A ‘hold timer expiry’ indicates that the router did not receive a keepalive (or any other BGP message) from its peer within the negotiated hold time. The most direct cause is a mismatch in the configured keepalive and hold timer values between the two peers. The BGP negotiation will use the lower of the two advertised hold times, but if one peer is configured with an extremely low hold time (e.g., 10 seconds) and the other is default (90 seconds), it can lead to instability. Checking and aligning these timers is a fundamental first step. While MTU or TTL issues can cause packet loss leading to expiry, they are less direct than a timer mismatch.

An EPIPE service using qinq encapsulation (often referred to as ‘Epipe with dot1q-tunneling’ or ‘Q-in-Q’) is the correct choice. It creates a point-to-point Layer 2 tunnel. The outer ‘S-Tag’ (Service Tag) is used by the service provider to identify the service within the MPLS core, while the customer’s inner ‘C-Tag’ (Customer Tag) is transparently carried. This completely hides the customer’s MAC addresses and VLAN topology from the core (MAC learning happens only on the customer-facing ports). It also allows the customer to use any VLAN ID at each site independently, as the service is essentially port-based from the provider’s perspective. Basic VPWS would map a specific customer VLAN to an MPLS VC, tying the service to that VLAN ID.

The core advantage of model-based, intent-driven automation (as implemented in NSP) is the shift from managing individual device configurations to declaring the desired state (the ‘intent’) of a network service. The system then computes and pushes the necessary, consistent configuration snippets to all involved devices. This eliminates configuration drift, ensures network-wide policy adherence, and dramatically reduces the errors introduced by manual, repetitive CLI configuration. While it may be faster, speed is a secondary benefit. Packet capture and automatic upgrades are separate functionalities.

In a VPRN, customer routes learned from the CE are installed in the local VRF. For them to be reachable from other sites, the PE must redistribute them into MP-BGP (VPNv4/VPNv6) and advertise them to other PEs. Therefore, if the route is in the local VRF but not reachable remotely, the issue is in the export/redistribution process or the BGP path to the remote PE. Checking the global routing table (specifically the BGP VPNv4 table) on the local PE will show if the route has been successfully converted into a VPN route and labeled. If it’s missing there, the problem is local to this PE (route-target export policy, redistribution). If it’s present, then the issue is downstream (BGP session, import policy on remote PE).

The Expedited Forwarding (EF) forwarding class is designed for low-loss, low-latency, low-jitter traffic like voice. It is typically served by a strict-priority scheduler (on Nokia platforms, often within a ‘priority’ level of a hierarchical scheduler). This means that any traffic in the EF queue is transmitted before any traffic from other, non-priority queues (like AF or BE), guaranteeing the required performance. Network Control is for routing protocols, Assured Forwarding provides guaranteed bandwidth but not strict priority, and Best Effort is for default, leftover traffic.

The fundamental difference is in what they synchronize. Synchronous Ethernet (SyncE) is an extension of Ethernet that distributes physical layer frequency synchronization (like SONET/SDH). It is very stable and accurate for frequency. Precision Time Protocol (PTP), specifically the telecom profiles like G.8275.1, is designed to distribute both precise frequency and phase/Time of Day (ToD), which is essential for technologies like TD-LTE and 5G TDD that require aligned transmission/reception windows. Option B is incorrect because modern PTP profiles often use telecom-boundary or telecom-transparent clocks. Option C is the reverse of the truth. Option D is incorrect; SyncE is Layer 1, PTP is a Layer 2/3 protocol.

Deep buffer memory is a significant feature of platforms like the 7250 IXR. Its primary purpose is to absorb large, sudden bursts of traffic (common in data center interconnect, internet peering, or video streaming scenarios) by queuing packets in memory during microsecond-level congestion events. This prevents immediate tail-drop, which is particularly harmful to TCP-based traffic as it causes global synchronization and throughput collapse. Instead, it allows traffic management algorithms like WRED to work effectively, improving overall link utilization and application performance. It is not used for route storage (that’s the FIB/RIB), content caching, or OS storage.

When an LSP ping succeeds but the trace shows a loop, it often indicates a forwarding plane issue where the data plane and control plane are out of sync. A common cause is a ‘forwarding adjacency mismatch’ in the IGP, where nodes have inconsistent views of the network topology or metrics for the LSP’s path. This causes the MPLS label to be swapped to a next-hop that then sends it back, creating a loop. While RSVP issues could cause setup failure, the success of the ping indicates the LSP is established. Static route misconfiguration is less likely for a signaled LSP, and load-balancing would cause out-of-order packets, not a consistent loop in a trace.0