CCIE CCIE Service Provider 1 — Questions and Answers
Question 1: In MPLS L3VPN, which protocol is used to distribute VPN labels and VPNv4 routes between PE routers?
- LDP
- RSVP
- MP-BGP (Correct answer)
- OSPF
Correct answer: MP-BGP
Multiprotocol BGP (MP-BGP) with the VPNv4 address family distributes customer routes and associated VPN labels between PE routers across the MPLS backbone.
Question 2: What is the purpose of a Route Distinguisher (RD) in MPLS L3VPN?
- Encrypting customer routes
- Making overlapping customer IP prefixes unique in the BGP table (Correct answer)
- Defining which routes to import into a VRF
- Assigning MPLS labels
Correct answer: Making overlapping customer IP prefixes unique in the BGP table
An RD prepended to customer IPv4 prefixes creates unique VPNv4 routes, allowing BGP to differentiate between identical prefixes from different VPN customers.
Question 3: What mechanism in MPLS service provider networks controls which VPN routes are imported/exported between VRFs?
- Route Distinguisher
- Route Target (RT) community (Correct answer)
- VPN label
- BGP confederation
Correct answer: Route Target (RT) community
Route Targets are BGP extended communities used to control VPN route import and export between VRFs, determining which sites can communicate.
Question 4: In a service provider network, which IS-IS level is used for routing within a single area?
- Level 0
- Level 1 (Correct answer)
- Level 2
- Level 3
Correct answer: Level 1
IS-IS Level 1 routing handles intra-area routing within a single IS-IS area, analogous to OSPF intra-area routing.
Question 5: What is the function of RSVP-TE (Resource Reservation Protocol - Traffic Engineering) in MPLS networks?
- Distributing IP routing information
- Signaling LSPs with bandwidth reservations for traffic engineering (Correct answer)
- Providing MPLS label distribution between adjacent routers
- Encrypting MPLS tunnels
Correct answer: Signaling LSPs with bandwidth reservations for traffic engineering
RSVP-TE signals explicitly-routed Label Switched Paths (LSPs) with bandwidth reservations, enabling traffic engineering in MPLS networks.
Question 6: Which BGP feature allows ISPs to aggregate customer routes and prevent specific customer prefixes from being advertised to the internet?
- BGP confederation
- BGP route reflectors
- BGP aggregate-address with summary-only (Correct answer)
- BGP communities
Correct answer: BGP aggregate-address with summary-only
The 'aggregate-address' command with 'summary-only' suppresses more-specific component routes and advertises only the aggregate to reduce internet routing table size.
CCIE CCIE Service Provider 1
In MPLS L3VPN, which protocol is used to distribute VPN labels and VPNv4 routes between PE routers?