300-510 Implementing Cisco Service Provider Advanced Routing Solutions (SPRI) Practice Questions

The Label Distribution Protocol (LDP) is the primary signaling protocol used in MPLS networks to automatically discover neighbors (LSRs) and exchange label-to-FEC (Forwarding Equivalence Class) mappings. When an IGP like OSPF or IS-IS establishes reachability to a prefix (the FEC), LDP is responsible for generating a local label for that FEC and advertising this binding to its LDP neighbors.

In Cisco IOS XR's Routing Policy Language (RPL), a community-set is used to define a named, reusable collection of BGP community values. This set can then be referenced within a route-policy to match against incoming communities or to set communities on advertised routes. This approach promotes modular and readable policy configurations. Prefix-sets are for matching network prefixes, and as-path-sets are for matching AS_PATH attributes.

The fundamental difference lies in how receivers join a multicast group. In ASM, a receiver sends an IGMP join for a group address (*,G) and will accept traffic from any source sending to that group. This model requires a Rendezvous Point (RP) to discover sources. In SSM, a receiver sends an IGMPv3 or MLDv2 join for a specific channel (S,G), explicitly identifying the source IP address (S) and the group address (G). This eliminates the need for an RP and provides better security and control.

This is the most direct and correct solution. When redistributing between two different routing processes (even two IS-IS processes), a route-map provides the necessary policy control. By creating two route-maps and applying them to the redistribute isis... commands on the border router, the administrator can match the desired routes (e.g., all routes via a permit statement) and use set metric +50 to add 50 to the existing metric before advertising them into the other domain. This is precise, scalable, and directly addresses the requirement.

PIMv2 Bootstrap Router (BSR) is an IETF standard (RFC 5059) and is supported by multiple vendors, making it ideal for a multi-vendor environment. Configuring multiple Candidate-RPs with the same priority allows for load balancing of multicast groups across the RPs using a hash algorithm, providing redundancy. Auto-RP is a Cisco-proprietary mechanism. Anycast RP with MSDP is a valid redundancy solution but is more complex to implement than BSR. Static RP configuration does not provide dynamic discovery or inherent redundancy.

In IS-IS on IOS XR, summarization from a Level 1 area into Level 2 is configured on the L1/L2 border router under the IS-IS process and the appropriate address family. The summary-prefix 10.10.0.0/16 level-1 into-level-2 command specifically instructs the router to summarize prefixes learned via Level 1 and advertise this summary into the Level 2 domain. The other options use incorrect syntax or commands (area-range is for OSPF) or lack the required direction (level-1 into-level-2).

Local Preference is the correct attribute for influencing outbound traffic path selection within a single AS. It is evaluated before AS path length in the BGP best path selection algorithm. By setting a higher Local Preference for the routes received over the preferred 10Gbps link, all routers within the provider's AS will choose that path to reach the customer prefix. MED is used to influence how other ASes enter the provider's network. AS path prepending influences inbound traffic from other ASes. Weight is local to a single router and not propagated, so it would not create a consistent policy across the AS.

The Segment Routing Mapping Server (SRMS) is the correct component for LDP and SR interworking. Its primary role is to advertise mappings between SR Prefix-SIDs and prefixes to LDP-only nodes. It effectively translates SR information into a format that LDP speakers can understand, allowing them to build LSPs towards destinations in the SR domain. A PCE is used for path computation, SRGB is the global block of labels for SR, and TI-LFA is a fast reroute mechanism.