Department of Information & Communications Technology HKIVE (TY) Broadband/High Performance Networks Tutorial #10 1. Which of the following statements are TRUE?

(I) A VRF table in a PE is associated with a customer site connected directly with to this PE.

(II) A VRF table in a PE is associated with a port. (III) A VRF table in a PE can be associated with one or more customer sites

connected directly to this PE. (IV) A VRF table in a PE can be associated with one or more ports. (V) A VRF table in a PE is usually configured to handle VPN information of one

directly connected customer site. (VI) A VRF table in a PE is usually configured to handle VPN information of one

or more directly connected customer sites.

2. List two types of data links that a CE router can use to connect to the service providers PE router.

3. List two protocols that a PE router in a BGP/MPLS VPN network can use to exchange routing information with its directly connected CE routers.

4. State the protocol that PE routers in a BGP/MPS VPN network used to exchange

VPN routing information 5. State THREE factors that can enhance the scalability of a service provider

BGP/MPLS VPN network. 6. Besides scaling, state another TWO issues that BGP/MPLS VPNs have to solve. 7. The VPN-IPv4 addresses are being used to solve the overlapping of customers

private IP address spaces. i) Draw a diagram to show the fields of an VPN-IPv4 address ii) What should the ADMINISTRATOR sub-field in a route distinguisher

hold when the value of the TYPE sub-field is 0? iii) What should the ADMINISTRATOR sub-field in a route distinguisher

(RD) hold when the value of the TYPE sub-field is 1? iv) State the protocol that a PE router uses to distribute its VPN-IPv4 addresses

to other PE routers within the VPN. v) Which of the following statements are TRUE?

(I) Each VRF table in a PE router within a VPN can have its own unique RD.

(II) VPN customers are aware of the use of VPN-IPv4 address. (III) VPN-IPv4 addresses are carried in MP-BGP that runs across the

service provider network. (IV) VPN-IPv4 addresses are carried in user data packets that traverse

across the service provider network. (V) VPN-IPv4 addresses are used both inside and outside a service

provider network. (VI) In addition to IPv4, MP-BGP carries routing information for other

network layer protocols like, IPX, IPv6, VPN-IPv4, etc.

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8. Service provider can constrain the flow of customer VPN data traffic by constraining the flow of VPN-IPv4 routing information. i) One way to constrain the flow of VPN-IPv4 routing information is by using

multiple VRF tables. With reference to figure 6.34 in notes, assume multiple VRF tables are used in each PE for per-VPN segregation of routing information and PE 2 imports customer B site 2s VPN B routes into VRF-B. Which of the following statement(s) is(are) TRUE? (I) PE 2 imports local customer A site 2s VPN A routes into VRF-B. (II) PE 2 imports remote customer A site 1s VPN A routes into VRF-B. (III) PE 2 imports remote customer A site 3s VPN A routes into VRF-B. (IV) PE 2 imports remote customer B site 1s VPN B routes into VRF-B.

ii) BGP extended community attributes are also used to control the distribution of routing information between PE routers. (a) Is a BGP extended community has to be globally unique? (b) How many BGP extended communities can a customer VPN use? (c) List the THREE types of BGP extended community attributes that

VPNs can use. (d) Assume Full-Mesh-A and Full-Mesh-B are two globally

unique route targets. Replace I, II, III, IV, V and VI in the diagram below with either Full-Mesh-A or Full-Mesh-B such that the service provider network provides full-mesh VPN connectivity for customer A.

9. When the configuration of a PE router is changed, e.g. adding a new VRF table, how

can this PE router trigger other PE routers in the same service provider network to re-transmit their routing information?

10. Briefly explain how the outbound route filters can be used to reduce the number of

routing updates and hence conserve the backbone bandwidth and the processing resources of PE routers.

11. With reference to figure 6.36 in notes,

i) list the two pieces of routing information PE 1 has to advertise to PE 2 for Customer Bs route to prefix 10.11/16

Customer A Site 1

CE 1 CE 2

Customer A Site 2

PE 1 PE 2

Exp Target = I Imp Target = II

Exp Target = III Imp Target = IV

Customer A Site 3

CE 4

PE 3

10.11/16 10.21/16

10.31/16

VRF-A

Service Provider Network

VRF-A

Exp Target = V Imp Target = VI

VRF-A

LSP

2

ii) list the two actions that PE 2 will perform after it receives from PE 1 the route advertisement for prefix 10.11/16.

iii) list the protocol that can be used to establish BEST-EFFORT LSPs from PE2 to PE 1.

12. With reference to the diagram below, assume:

- PE 1 can send user data traffic to PE 2 using LSP 1 - the initial MPLS label for LSP 1 at PE 1 is 121 - the MPLS label that associates VRF-B at PE 1 to the port that connects CE5

is 715 - PE 2 can send user data traffic to PE 1 using LSP 2 - the initial MPLS label for LSP 2 at PE 2 is 211 - the MPLS label that associates VRF-B at PE 2 to the port that connects CE3

is 823 - I, II, III & IV represent MPLS labels Based on the assumption above, replace I, II, III and IV with valid values for successful transportation of user data between site 1 and site 2 of customer B.

Customer B Site 2

PE 1

CE 5 CE 3

PE 2

13. State THREE benefits of BGP/MPLS VPNs when compared with other L2 VPN

technologies. 14. State ONE disadvantage of BGP/MPLS VPNs. 15. Which of the following statements are TRUE?

(I) Pseudo-wire (PW) is a circuit leased line concept standardized by ITU-T. (II) Pseudo-wire (PW) is a packet leased line concept standardized by IETE. (III) An Ethernet PW allows Ethernet frames not including preamble and FCS to

be carried over a packet switched network. (IV) An Ethernet PW allows Ethernet frames including preamble and FCS to be

carried over a packet switched network. (V) A PW terminates a logical port within a PE. (VI) A PW terminates a physical port within a PE. (VII) The terminating port of an Ethernet PW in a PE provides an IP-address based

transportation service (VIII) The terminating port of an Ethernet PW in a PE provides an Ethernet MAC

based transportation service (IX) An Ethernet PW can be setup via manual configuration (X) An Ethernet PW can be setup using signaling protocol like BGP or LDP (XI) A packet switched network (PSN) tunnel can only support one PW.

CustomSite 1

10.11/1

er B

6 10.21/16

Service Provider Network

LSP 2 VRF-B

VRF-B LSP 1

III IV user data

user data II I

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(XII) With reference to figure 6.37 in notes, P1 and P2 need to have information about the L2 services provided by PE 1 and PE 2.

(XIII) With draft-martini encapsulation, a PW can be constructed by building a bi-directional virtual connection LSP.

(XIV) With draft-martini encapsulation, a PW can be constructed by building a pair of uni-directional virtual connection LSPs.

(XV) The ingress PE and egress PE in an LDP session that is setup with targeted LDP must be directly connected with each other.

16. A PW can be configured in one of the two modes of Ethernet encapsulation. List

these two modes of Ethernet encapsulation. 17. Does a PW support frame re-ordering? 18. LDP and MPLS LSP are used to setup a PW

i) State four types of virtual connection (VC) information exchanged between two PEs in a targeted LDP session for setting up a PW.

ii) How many MPLS LSPs are needed between two PEs to support one PW? iii) With reference to figure 6.40 in notes,

i) what is the VC label PE 1 sends to PE 2 in the targeted LDP session for setting up the PW?

ii) what is the VC label PTE 2 sends to PE 1 in the targeted LDP session for setting up the PW?

iii) what is the LSP label PE 2 sends to P 2 for setting up the LSP from PE 1 to PE 2?

iv) what is the LSP label P 1 sends to PE 1 for setting up the LSP from PE 1 to PE 2?

19. Which of the following statements are correct?

(I) VPLS does not allow an enterprise customer to be in full control of its WAN routing policies.

(II) VPLS allows an enterprise customer to be in full control of its WAN routing policies.

(III) VPLS uses L2 emulated LANs to transport any type of traffic (IV) VPLS uses L3 emulated LANs to transport any type of traffic (V) A PE in an MPLS domain can participate in ONLY ONE VPLS domain. (VI) A PE in an MPLS domain can participate in MORE THAN ONE VPLS

domain. (VII) To a CE, a VPLS domain looks like a router. (VIII) To a CE, a VPLS domain looks like an Ethernet switch. (IX) An LSP can ONLY be used by ONE VPLS domain. (X) An LSP can be used by more than one VPLS domains and other services.

20. State 4 requirements for VPLS. 21. Briefly describe the main difference in the signaling mechanism between the P2P

martini model and VPLS 22. Briefly describe how to avoid loops in a VPLS domain. 23. With reference to figure 6.43:

i) At PE 1, which of the following statement is correct? (I) PE 1 associates MAC address 080003009876 with VC-LSP

(102).

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5

(II) PE 1 associates MAC address 080003009876 with VC-LSP (201).

(III) PE 1 associates MAC address 080003009876 with the local Ethernet port connecting to CE 1.

ii) At PE 2, which of the following statement is correct? (I) PE 2 associates MAC address 080003009876 with VC-LSP

(201). (II) PE 2 associates MAC address 080003009876 with VC-LSP

(102). (III) PE 2 associates MAC address 080003009876 with the local

Ethernet port connecting to CE 2. iii) At PE 3, which of the following statement is correct?

(I) PE 3 associates MAC address 080003009876 with VC-LSP (301).

(II) PE 3 associates MAC address 080003009876 with VC-LSP (103).

(III) PE 3 associates MAC address 080003009876 with VC-LSP (302).

(IV) PE 3 associates MAC address 080003009876 with VC-LSP (203).

(V) PE 3 associates MAC address 080003009876 with the local Ethernet port connecting to CE 3.

24. With reference to figure 6.41,

i) how many forward information base does PE 1 have to maintain? ii) how many forward information base does PE 3 have to maintain?

25. Briefly describe the difference between unqualified and qualified MAC address

learning in VPLS. 26. i) What is auto-discovery in VPLS?

ii) A mechanism using BGP extended communities is used for auto-discovery in VPLS. State the information exchanged among PEs using BGP extended communities for auto-discovery in VPLS.

Department of Information & Communications TechnologyHKIVE (TY)Broadband/High Performance Networks Tutorial #10