TDC 560 Networking Assignment

For questions 1 – 8, refer to the network diagram below. In the network, R2, R3 and R4 are MPLS Label Switched Routers (LSRs). They use OSPF as an IGP and LDP for label distribution. These LSRs use per-platform label space, unsolicited downstream label distribution, liberal label retention mode. Each router has a /32 Loopback0 address that is used as its LSR ID. The four serial links are /30 subnets. The interface IP addresses are shown in the address table. Assume OSPF has converged so all routing tables are up-to-date. Bandwidth speeds, marked on figure, have been configured on serial interfaces, which determine OSPF link costs. Loopback interface OSPF costs are 1.

1. (10%) Fill in contents of the Router R1 Routing Table below. Each row corresponds to the nine IP subnets in the network diagram.

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2. (10%) Now the four routers in the same network assign Local Labels to each of the 9 subnets in their routing tables as shown in this Local Label Table. Assume that PHP is not

Now the LDP protocol executes so that the Label Information Base (LIB) tables on all routers are up to date. Show the contents of the Router R1 LIB. Assume that PHP is not used.

3. (10%) Based on values in its Routing Table and LIB, each router now computes its Label Forwarding Information Base (LFIB). Show the contents of the Router R1Your Next Hop must be an IP address or blank. Assume that PHP is not used.

4. (4%) Now, using LFIB from #2(b), consider a packet sent by R1 to destination 160.2.0.10. This packet will go over Link 1 and Link 3.
   1. What MPLS label value, if any, will be in the header of this packet as it passes over Link 1?
   2. What MPLS label value, if any, will be in the header of this packet as it passes over Link 3?

5. (10%) Now go back and repeat problem #2 assuming that PHP is When PHP is active, the assignment of Local Labels will be different than the Local Label table shown in problem #2, because IMP-NULL values will be in the Local Label table. Show a feasible Local Label table (5 columns, 9 rows) that assigns local labels to each of the 9 subnets on R1, R2, R3 and R4 when PHP is used.

6. (10%) Using your Local Label table from answer #5, now go back and repeat the building of the LIB as in problem #2 assuming that PHP is Show the contents of the Router R1 LIB using PHP.

7. (6%) Now, using the routing table you derived in question #1 and the LIB from #6, show the contents of the Router R1 LFIB, assuming that PHP is

8. (4%) Now, using LFIB from #7, consider a packet sent by R1 to destination 160.2.0.10.
   1. What MPLS label value, if any, will be in the header of this packet as it passes over Link 1?
   2. What MPLS label value, if any, will be in the header of this packet as it passes over Link 3?

For questions 9 – 17, refer to the network diagram below. The BigIP ISP network contains 5 PE LSRs (R1 – R5). BigIP uses OSPF to synchronize global routing tables among these 5 routers. BigIP has two corporate customers:

• Gordon Corporation has 4 customer sites, which are connected to BigIP PE routers R1, R2, R3, R5, respectively
• Blatchley Enterprises has one customer site connected to BigIP PE router R4. R4 redistributes eBGP over OSPF and vice-versa.

Each customer site has a Customer Edge (CE) router, which runs eBGP with its directly-connected PE. The 4 Gordon sites are connected together as a single 4-site Virtual Private Network (VPN). BigIP configures layer 3 MPLS VPN service on LSRs R1, R2, R3 and R5 to provide this VPN service to Gordon sites. PHP is enabled. The Blatchley site is not on any VPN.

9. (4%) How many VRF interfaces are there in the network diagram? Name (router name & interface name) of each router interface on the diagram which is a VRF interface.

10. (6%) Out of the 5 numbered IP subnets shown in the diagram:
    1. Which of these subnets will be in the router R3 global routing table?
    2. Which of these subnets will be in the router R3 VRF routing table?
    3. Which of these subnets will be in the routing table of the Gordon CE connected to R5?

A packet is sent from source IP 40.1.23.9 to destination IP 40.1.20.156. When LSR R5 receives this packet on interface S0/0, it will push two labels (VPN and LDP label) onto the packet and send it out interface S0/2.

11. (2%) Why are 2 labels needed? What is the purpose of each label?

12. (2%) Which of the following table does LSR R5 look up these two label values before forwarding the packet:

VRF routing table or

global routing table or

VRF CEF table or

global CEF table or

LFIB table

13. (2%) When LSR R2 receives this labeled packet which label will it look up in its LFIB – the VPN label or the LDP label?

14. (2%) How many labels will this packet have on the hop from R2 to R1?

15. (4%) How did LSR R5 learn the value of the VPN label? What protocol was used to advertise (distribute) this label value? Which LSR was the source of the packet that advertised this label value?

16. (4%) How did LSR R5 learn the value of the LDP label? What protocol was used to advertise (distribute) this label value? Which LSR was the source of the packet that advertised this label value?

17. (4%) How many BGP peer sessions (that is, how many 2-way TCP connections) are established between BigIP routers to provide this VPN service?

18. (4%) Under MPLS TE, the setup of one tunnel can “preempt” an already-established tunnel. That is, the setup of a new tunnel can cause an established tunnel to be taken down so that bandwidth can be freed up to establish the new tunnel. Under what conditions can this preemption occur? When preemption occurs, what router is responsible for re-establishing the tunnel that got taken down?

19. (4%) There are 3 protocols that can advertise MPLS label values – LDP, BGP and RSVP. When a TE Tunnel is set up using explicit setup, which protocol is used to advertise the TE Tunnel label values to the LSRs along the tunnel path?