3-2 - MP-BGP Routing Requirements in MPLS VPNs

Question 1

T/F: MP-BGP is capable of carrying VPNv4 (96-bit) prefixes in addition to other address-families.

Answer 1

True

Question 2

What is the unique 64-bit value within the VPNv4 address called?

Answer 2

route distinguisher (RD)

Question 3

T/F: The VPNv4 addresses are exchanged between PE routers and CE routers.

Answer 3

False. The VPNv4 addresses are exchanged only between PE routers and never between CE routers.

Question 4

What are the 64-bit extended communities included in a VPNv4 announcement called and used for?

Answer 4

route targets (RT). They’re used to control what prefixes get added into which VRFs upon being received by remote PEs.

Question 5

The MPLS VPN architecture uses the BGP routing protocol in two distinct ways. Describe them.

Answer 5

• VPNv4 routes propagate across an MPLS VPN backbone by using MP-BGP between PE routers.
• You can use BGP as the PE-CE routing protocol to exchange VPN routes between the PE and CE routers.

Question 6

IOS/IOS-XE and IOS-XR command:
address-family ipv4

Answer 6

in router BGP subconfig mode, this activates the IPv4 address-family and enters AF subconfig mode

Question 7

IOS/IOS-XE and IOS-XR command:
address-family ipv6

Answer 7

in router BGP subconfig mode, this activates the IPv6 address-family and enters AF subconfig mode

Question 8

IOS/IOS-XE and IOS-XR command:
address-family [vpnv4 | vpnv6] [unicast | multicast]

Answer 8

in router BGP subconfig mode, activates the VPNv4 and/or VPNv6 AF for unicast and/or multicast traffic

Question 9

In an L3VPN, the PE router performs 3 main tasks. What are they?

Answer 9

• Exchanges routing updates with the CE router
• Translates the CE routing information into VPNv4 and VPNv6 routes
• Exchanges VPNv4 and VPNv6 routes with other PE routers through MP-BGP

Question 10

T/F: iBGP requires a full-mesh of adjacencies due to the BGP split-horizon rule.

Answer 10

True

Question 11

What is the formula to determine how many iBGP sessions are needed (given n number of routers)?

Answer 11

(n * (n - 1)) / 2

where n is the number of routers.

Question 12

What are BGP route reflectors?

Answer 12

BGP route reflectors enable a much higher level of scalability, since a router can advertise or reflect iBGP learned routes to other iBGP speakers to circumvent the BGP split-horizon rule.

Question 13

IOS-XR command:
neighbor [ipv4-address | ipv6-address | peer-group-name] route-reflector-client

Answer 13

Configures a neighbor as a route-reflector client, causing this local BGP system to act as the route-reflector server for that neighborship.

Question 14

IOS/IOS-XE command:
address-family ipv4 vrf [vrf-name]

Answer 14

• Under router BGP subconfig mode, activates a VRF-specific IPv4 address-family and enters the subconfig mode for that AF
• The BGP neighbor to a CE would be activated under this AF.

Question 15

IOS-XR command:
vrf [vrf-name]

Answer 15

Under the router BGP subconfig mode, enters a VRF-specific subconfig mode

Question 16

IOS-XR command:
vrf [vrf-name] address-family ipv4 unciast

Answer 16

Under the router BGP subconfig mode, enters a VRF-specific subconfig mode and then activates the IPv4 address-family under it (entering that VRF and AF subconfig mode)

Question 17

Which of the following is the MP-BGP VPNv4 (96-bit) prefix?

A. route distinguisher
B. route reflector
C. unicast prefix
D. multicast prefix

Answer 17

A