Examination IP routning inom enkla datornät, DD2490 IP routing in simple networks, DD2490 KTH/CSC Date: 24 May :00 19:00

Transcription

1 Examination IP routning inom enkla datornät, DD490 IP routing in simple networks, DD490 KTH/CSC Date: 4 May 00 4:00 9:00 a) No help material is allowed - You are not allowed to use books or calculators! b) You may answer questions in English or in Swedish. c) Max points is 50, Limit for passing (Grade E) is 5. d) Bonus points will be awarded only if you pass the exam. e) Course responsible is Olof Hagsand, phone

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3 . Routers and routing (0p) Answer briefy:. In a communication network, what is "protection switching"? (p). In an operator network, what is "transit" trafc? (p). What is a "tier " operator? / How is it defned? (p) 4. What is the purpose of a multicast "rendez-vous point"? (p) 5. What is MPLS label stacking? (p) 6. Name one signifcant diference between IS-IS and OSPF areas. (p) 7. What is the diference between a regular OSPF area and a stub OSPF area? (p) 8. What is the diference between source-specifc multicast (SSM) and any-source multicasting (ASM)? Which is most common today? (p) 9. What is pen-ultimate popping in MPLS? (p) 0. Which are the three most signifcant identifers of a STP priority vector? (p). Addressing (5p) H H R R R R4 R5 R6 Regard the network in the fgure consisting of routers R-R6 interconnected by Ethernet links with interface names (,..) as shown. There are two hosts H and H. There are fve Ethernet links. Note that the link interconnecting R5 and R6 is an Ethernet link. Make a minimal address allocation of the network above. Use the block.0.0.0/4, and try to allocate as few addresses as possible, starting from the lowest adress possible. Include both hosts and routers in the allocation. ) Which blocks have you allocated (denote the address blocks using CIDR notation - address/prefxlen)? (p) ) Create a minimal aggregated block that you can use to advertize your network to the rest of the world. Which is your aggregated

4 address block that incorporates all sub-blocks in the previous exercise?(p) Note that you must complete this exercise in a correct way in order to be awarded points in the following exercises.. Distance-vector and RIP (5p) Suppose RIPv (Routing Information Protocol) is run on all routers in the previous exercise (Exercise ). Assume also that RIP runs with splithorizon but not poison reverse. Which messages and which distancevectors are sent by router R5 to its neighbours? Specify outgoing interface, distance vector content (prefx, metric, next-hop). Also specify which destination adress the RIP messages have. All link metrics are one. 4. OSPF (5p) Assume you run OSPF on the network below which is reduced version of the network in Exercise. Use the same addressing as in Exercise. R R R R4 R5 R6 Again, all link metrics are. Assume also that R6 runs BGP to the rest of the internet and imports the following two routes from into OSPF:.0.0.0/8 and.0.0.0/8. The AS-path lengths of the imported routes are both 7. Let router-id follow router name (e.g., R has router-id ). Also, let highest router-id be designated router in a transit network. Assume you run the network as a single backbone area. List the OSPF LSAs in router R5. You should specify for all LSAs: LS type, LS identifer, and advertizing router. For router LSAs, specify link type and link id for each associated link. For network LSAs specify netmask and connected router ids. For summary and external LSAs, specify mask and metric. 5. OSPF Areas (5p) Using the same network as in the previous exercise (Exercise 4), create two new regular areas ( and ) with R5 and R6 as border routers respectively. Area 0 consists of R5 and R6 and their interconnection only. a) List the LSAs in R5 for area. (p) b) If area and are transformed to stub areas, which changes to the LSAs in area are made? (p)

5 6. Multicast (5p) Regard again the network in Exercise. Now, all routers run PIM-SM and an internal routing protocol such as OSPF. The two routers R4 and R5 run Anycast-RP and MSDP. Routers R, R, and R5 use R5 as RP, while R, R4, and R6 use R4 as RP. Assume H sends multicast trafc to group 9..., and that H has joined the group. All link-metrics are. List the multicast forwarding entries: (Sender, Group)/ Outgoing i/f list, of the routers in a table in the following two situations: a) Sources have been detected by the RPs via MSDP, source trees are established, and the shared (RP-) tree has been established to the receivers. (p) b) After tree-switchover (shared tree sourcetree) has taken place. (p) 7. Spanning-tree (5p) Study the switched network with learning bridges running spanning-tree protocol below with bridge IDs and port numbers as indicated. All link metrics have the value one. Note the segment between and 4 which is a shared Ethernet with four ports connected to it. Show (or describe) the spanning-tree of the network, indicating root, designated and blocked ports. You can use the notation given in the fgure root port designated blocked/listening/ forwarding

6 8. MPLS (5p) Suppose you operate an IP network. It runs BGP with its neighbour ASs, and your task is to confgure it for transit trafc with a BGP-free core. MPLS LSPs should be used for the transit trafc. Outline and exemplify how such a network is set up. Draw a fgure of a non-trivial example network (use for example four border routers and at least two core routers). You should cover which routing protocols run on which routers and the purpose of each protocol. How are the LSPs setup (between which routers)? You should also explain how the border-routers diferentiate between transit trafc and IP trafc, i.e., how is transit trafc sent via MPLS LSPs and IP? Also describe how you can setup trafc engineering in order to use the resources in the network better. 9. Protection switching(5p) Compare the following protocols with respect to protection switching: OSPF, MPLS, Spanning-tree. How does fault detection and protection switching work in each protocol? Which variants exist? How can protection switching be optimized, that is, how can the time for fail-over be reduced?