1-5 - MPLS VPN Control Plane Operation

Question 1

What are the characteristics of a VRF (virtual routing and forwarding) table?

Answer 1

• virtual, carved out routing table for a specific customer
• the interface that is part of the VRF must support CEF
• you can associate a single interface (logical or physical) with only one VRF

Question 2

What are the characteristics of Deterministic Large VRF support?

Answer 2

• available on Cisco ASR9000 series routers
• allow several prefixes per VRF, up to global FIB size

Question 3

What are Route Distinguishers?

Answer 3

• 64 bit unique identifier that prepends to a 32-bit customer route (if IPv4) to make a unique 96 bit network address
• the purpose is to make the customer prefixes unique within the entire MPLS domain
• called VPNv4 for IPv4 and VPNv6 for IPv6

Question 4

T/F: VPNv4 addresses are exchanged only between PE routers and are never sent to or received from CE routers.

Answer 4

True

Question 5

T/F: MP-BGP sessions are used to exchange VPNv4 and VPNv6 routes.

Answer 5

True

Question 6

What is a Route Target?

Answer 6

A BGP extended community value, where the high-order 16 bits are used to encode a value that corresponds to the VPN membership of that specific site.

Question 7

What are example formats of an RD?

Answer 7

<AS number : VPN identifier>… ex: 3737:1000
<IP address : VPN identifier>… ex: 10.7.3.1:1000

Question 8

What are example formats of a Route Target?

Answer 8

<ASN : arbitrary value>… ex: 3737:1000
<IP address : arbitrary value>… ex: 10.7.3.1:1000

Question 9

What is a LIB (label information base)?

Answer 9

contains local assigned labels and learned labels from neighbors for each IP prefix in the RIB

Question 10

What is an LFIB (label forwarding information base)

Answer 10

a combination of the FIB and LIB
it contains info on the following for each prefix in the RIB/FIB:
- IP prefixes
- label values
- outgoing interface

Question 11

Provide examples of label exchange protocols.

Answer 11

-LDP (label discovery protocol)
-Cisco Tag Distribution Protocol
-BGP
-RSVP (when using MPLS TE)
-ISIS/OSPF extensions (when using Segment Routing

Question 12

Which of the following has the primary function to keep overlapping IPv4 addresses globally unique?
A. route target
B. route distinguisher
C. LDP
D. LSP

Answer 12

B

Question 13

Which of the following supports sites that participate in more than one VPN?

Answer 13

A. route distinguisher
B. LDP
C. LSP
D. route target