Hcip-Datacom-Advanced Routing & Switching Technology Free Sample Questions

To prevent routing loops in a BGP route reflector environment, the RR adds two key non-transitive BGP attributes. It adds the CLUSTER_ID, which identifies the reflection cluster. It also adds the ORIGINATOR_ID, which is set to the Router ID of the client that originally sent the route to the RR. If a router receives a reflected route containing its own Router ID as the ORIGINATOR_ID, it discards the route, thus preventing loops.

SLAAC relies on two key ICMPv6 messages from the Neighbor Discovery Protocol. First, a host sends a Router Solicitation (RS) message to the all-routers multicast address to prompt any local routers to respond immediately. In response, or periodically, a router sends a Router Advertisement (RA) message containing the network prefix and its length. The host combines this prefix with its own interface identifier (often a modified MAC address, EUI-64) to form a complete global unicast address.

This statement is false. The Route Distinguisher's (RD) sole purpose is to make customer prefixes globally unique within the provider's network, allowing for overlapping IP address spaces between different customers. It is the Route Target (RT), an extended community attribute, that controls the import and export of routes into and out of VRFs.

6PE is the ideal solution for this scenario. It leverages the existing IPv4 MPLS backbone without requiring any changes to the P routers. PE routers use MP-BGP to exchange IPv6 reachability information over their IPv4 peering sessions. IPv6 packets are encapsulated with two labels: an inner label for the destination PE (assigned by BGP) and an outer label for the next-hop P router (assigned by LDP). The IPv4-only P routers simply perform label switching based on the outer label, transparently forwarding the encapsulated IPv6 traffic. This is highly scalable and integrates perfectly with the MPLS infrastructure.

In the ExStart state, OSPF neighbors decide the master/slave relationship and the initial DD sequence number for exchanging database description (DBD) packets. If the MTU of the interfaces differs, the larger DBD packets from the router with the higher MTU might be dropped by the router with the lower MTU. This prevents the DBD exchange process from completing, causing the adjacency to remain stuck in ExStart. While OSPFv3 does not have a built-in MTU check like OSPFv2 for broadcast networks, an MTU mismatch will still cause the exchange of large DBD packets to fail.

The Overload bit is a mechanism used by an IS-IS router to signal to its neighbors that it is under stress (e.g., low memory, high CPU, or during a graceful restart) and should not be used for forwarding transit traffic. When other routers see the OL bit set in an LSP, they will still include the router's directly connected prefixes in their SPF calculations, but they will not calculate paths through the overloaded router to reach other destinations. This gracefully removes the router from the transit path without causing a full network reconvergence.

Standard QinQ maps all C-VLANs on a port to a single S-VLAN. To achieve Selective QinQ where different customers on the same port are mapped to different S-VLANs, a more granular method is needed. Since both customers use the same C-VLANs, matching on VLAN ID is insufficient. The typical method is to use a traffic policy that classifies traffic based on the source MAC address of the customer's equipment. An ACL can match the source MAC, and the associated traffic behavior can then remark the packet with the appropriate S-VLAN tag (100 for Customer A, 200 for Customer B).

The BGP state machine progresses through several states. The 'Connect' state specifically means that the local BGP process has initiated a TCP connection (sent a SYN packet) to its peer on port 179 and is now waiting for the peer to complete the TCP three-way handshake (by responding with a SYN-ACK). If the session remains in this state for an extended period, it typically indicates a lower-level connectivity issue, such as a firewall blocking TCP port 179, an incorrect peer IP address, or a routing problem preventing the SYN packet from reaching the peer.

A robust rollback plan is critical for any network change. It must include: 1) A saved, known-good configuration of the old device to restore its state. 2) A clear, step-by-step physical and logical plan to revert the change, including cabling and configuration steps. 3) Pre-defined, objective criteria (e.g., 'if critical application X is unreachable for more than 5 minutes', 'if BGP peerings do not establish within 10 minutes') that clearly define when to abandon the cutover and execute the rollback. A list of new features is part of the implementation plan, not the rollback plan.

LDP establishes a TCP session between neighbors to exchange labels. The source IP address for this session is called the transport address. On Huawei devices, the transport address is determined by the MPLS LSR-ID. If the LSR-ID is explicitly configured, that IP address is used. If not, the router automatically selects an IP address to be the LSR-ID (typically the highest IP address of a loopback interface) and uses that as the transport address. Using a stable loopback address as the LSR-ID is a best practice.