A fundamental advantage of segment routing (SR-MPLS) is that it removes the dependency on LDP or RSVP-TE for label distribution. The path is encoded as a list of segments (labels) in the packet header, with the IGP (ISIS or OSPF) distributing these segment identifiers. This simplifies the control plane significantly.

When BGP sessions are stuck in Active, it typically indicates a TCP connection issue. After confirming basic IP reachability, a mismatch in MD5 authentication (if used) is a very common culprit that will prevent the TCP 3-way handshake from completing, without generating a clear log message. Checking this before restarting processes or re-verifying core IGP reachability is the most efficient step.

The Route Distinguisher’s sole purpose is to take a non-unique IPv4 route and create a unique VPNv4 address for BGP. The Route Target is an extended community attached to the VPNv4 route that acts as a tag. Import/Export policies on PE routers use these RT tags to control which VPRN instances receive which routes, enabling the construction of overlay topologies.

The ‘leak-import’ policy under ‘config>router>isis>level1’ is the precise and controlled mechanism for route leaking in Nokia SR OS. It allows you to define a policy (e.g., matching specific prefixes with a prefix-list) to select exactly which Level 2 routes should be imported into the Level 1 link-state database, avoiding the flooding of the full Level 2 table.

In a typical PPPoE-based broadband network, the BNG and the access node use the combination of the MAC address and the PPPoE Session ID to uniquely identify a subscriber’s session and map it to the correct service (e.g., using a host-connectivity-verification policy). The VLANs provide aggregation and transport, but the session ID is crucial for service-level delineation on a shared access port.

In the hierarchical model, the aggregate scheduler (e.g., at the VPLS service level) defines the total bandwidth envelope for that service. Configuring a priority queue (like ‘priority-mode’) within this aggregate scheduler ensures that high-priority traffic (voice) is served first from the service’s allocated bandwidth, but is still constrained by that aggregate limit. This prevents it from consuming port-level bandwidth and starving other services.

In a VPLS multicast scenario using PIM, the VPLS acts as a single multi-access LAN. PE-2 must have an (S,G) entry showing the correct upstream neighbor (which should be PE-1, the PE closest to the source). If it shows 0.0.0.0 or a different neighbor, there is a PIM neighbor discovery or designated forwarder issue within the VPLS. This is a core PIM-SM check within the VPLS context.

BGP-LU is a specific BGP address family (labeled-unicast). To control which labeled prefixes are sent to a BGP-LU peer, you must apply an export route policy specifically in the context of that family for that neighbor (config>router>bgp>group>neighbor>family>labeled-unicast>export). This allows precise control over BGP-LU advertisements independent of the IPv4 unicast family.

Slope Policies in Nokia’s Hierarchical QoS (H-QoS) model define congestion thresholds (like ‘high’ and ‘exceed’) for a queue or scheduler. As queue depth rises past the ‘high’ threshold, the system can start dropping lower-priority traffic (using drop probability) *before* the queue is completely full, providing proactive congestion management and signaling to TCP flows to slow down, thus avoiding tail-drop scenarios.

A fundamental advantage of segment routing (SR-MPLS) is that it removes the dependency on LDP or RSVP-TE for label distribution. The path is encoded as a list of segments (labels) in the packet header, with the IGP (ISIS or OSPF) distributing these segment identifiers. This simplifies the control plane significantly.0