CCIE Service Provider Flashcards

Which Cisco IOS-XR feature provides sub-50ms failover for IP/MPLS networks by pre-computing alternate paths?

Answer: TI-LFA (Topology-Independent Loop-Free Alternates)

TI-LFA pre-computes repair paths for all protected prefixes using a P-space and Q-space calculation, providing sub-50ms local repair upon link/node failure.

What is BFD (Bidirectional Forwarding Detection) used for in service provider networks?

Answer: Sub-second failure detection for routing protocol adjacencies

BFD provides fast failure detection (milliseconds) for any forwarding plane path, enabling routing protocols to react to failures much faster than their own hello timers.

In service provider BGP, what is the purpose of the 'next-hop-self' command on route reflectors?

Answer: Setting the BGP next-hop to the RR's address for IBGP clients

The 'next-hop-self' command on an RR sets its own IP as the BGP next-hop, ensuring IBGP clients can reach the next-hop through the IGP without needing external next-hops.

What QoS mechanism is used by service providers to guarantee bandwidth and bound latency for real-time traffic like voice?

Answer: DiffServ with Per-Hop Behaviors (EF for voice)

DiffServ Expedited Forwarding (EF) PHB provides a low-latency, low-loss queue for voice traffic by guaranteeing bandwidth and using strict priority queuing.

In MPLS, which protocol uses link-state advertisements to distribute TE constraints like available bandwidth and link delay?

Answer: RSVP-TE with OSPF-TE/IS-IS-TE extensions

RSVP-TE relies on OSPF-TE or IS-IS-TE extensions (opaque LSAs/TLVs) to flood TE information like bandwidth and link delay throughout the topology.

What is Ethernet VPN (EVPN) primarily used for in service provider and data center networks?

Answer: Multi-homed Layer 2 VPN with BGP control plane for MAC/IP learning

EVPN uses BGP as the control plane for MAC/IP address learning, providing multi-homed active-active L2 VPN with efficient flooding suppression.