Cisco Advanced Service Provider


  • An engineer is implementing an MPLS within the core of the Service Provider network. LDP and OSPF/IS-IS are required to build the control and data plane for MPLS Label Switched Paths.
  • The mechanisms for distributing LDP are LDP and RSVP.
  • An engineer needs to implement changes to Router_A during a maintenance window. The engineer first saves the running-configuration of all routers to the local disk0, then applies the required configuration changes. However, during post checks, the engineer realizes the implementation was deployed on Router_B instead. configure replace disk0:config-1 command should the engineer apply to reverse the changes made during the maintenance window.
  • While evaluating a new hardware rollout plan before deployment, NEBS standards should review to ensure that the hardware met certain environmental design guidelines.
  • In inter-AS multicast, MP_REACH_NLRI and MP_UNREACH_NLRI optional nontransitive path attributes were introduced in BGP to carry unicast and multicast routing information for RPF check at the AS borders.
  • The XYZ service provider network is composed of hundreds of routers that run OSPF and LDP. Label acceptance control and Label allocation control LDP features can be used to increase peering update performance and reduce local memory consumption.
  • MPLS TE Fast Reroute (FRR) link protection operation:
    • It requires a next-hop backup tunnel.
    • The restoration time is expected to be under 50 ms.
    • The backup tunnel can have associated bandwidth capacity.
    • The point of local repair (PLR) swaps the label and pushes the backup label.
  • MPLS Layer 3 VPNs: Inter-AS and CSC Configuration Guide:
  • The show ip ospf database external command displays information about OSPF LSA type 5.
  • BFD for IS-IS IOS commands - In case the primary link fails, the convergence time should be less than a second:
    • isis bfd
    • bfd interval 250 min_rx 250 multiplier 3
  • Such as chassis-control, switch fabric, and fans components are shared among SDR.
  • A virtual network function describes a service function as defined in SDN.
  • Two OSPF neighbour routers are stuck in the EXSTART state. After a while, the neighborship goes down. A network engineer is debugging the issue when both routers show the OSPF log message "too many retransmissions. Interface MTU mismatch is the possible root cause.
  • Discard-class and QoS-Group QoS marking methods can a service provider use to mark user traffic and be visible only internally to the router.
  • The MPLS Inter-AS VPN options:
    • A: ASBR peers are connected by multiple subinterfaces with at least one interface linked to a VRF.
    • B: MP-BGP is used to distributed labelled VPN prefixes between the ASBRs.
    • C: RRs peering between ASs are used to distribute VPN prefixes.
    • AB(D): Single MP-BGP session between ASBRs in the global routing table carry control plane traffic, data plane traffic on VRF table.
  • Configuring SONET/SDH Alarms:
  • The QoS characteristics & mechanism:
    • replenishes token bucket continuously
    • can be implemented inbound on interfaces
    • does not support overhead accounting
    • replenishes token bucket on intervals
    • may increase the latency of traffic
    • must be implemented on CEs when a service provider rate limits a circuit
  • Though varying degrees of routing virtualization exist, there are two main techniques for creating virtualized router entities as defined by their physical and operational characteristics. A Hardware-Isolated Virtual Router (HVR) and a Software-Isolated Virtual Router (SVR).
  • In order to validate update messages that contain the BGPsec_Path attribute, the recipient must have access to two pieces of data that are obtained from valid RPKI (Resource Public Key Infrastructure) certificates and ROAs (Route Origin Authorizations):
    • the AS number and the list of IP address prefixes for each valid ROA
    • the AS number, public key, and subject key identifier for each valid RPKI router certificate

  • Configuring IEEE 802.1ad:
  • Characteristics of P2MP RSVP-TE and mLDP:
    • LSPs build from headend to tailend & LSPs are build from tailend to headend
    • Supports only P2MP LSPs & Supports P2MP and MP2MP LSPs
    • Supports traffic engineering & Supports FRR through unicast P2P TE
    • Signalling is periodic & No periodic signalling
    • P2P technology at control plane & Control plane is P2MP or MP2MP
    • P2MP at the data plane & Data plane is P2MP
  • Understand "include-connected" keyword use in IPv6 redistribution:
  • OSPF IPv6 routing requires OSPF version 3 which introduces two new LSA types: Link LSA (type
    and Intra-area Prefix LSA (type 9).
  • Preventing the AS from becoming a Transit AS path set community no-export additive command should be used within the route map. No-advertise says do not advertise to any other router but no-export says do not advertise to external neighbours, is ok to advertise to internal neighbours.