AR1718 test1 - Teste 1 de 2017/2018 professor João Miguel Ascenso PDF

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Teste 1 de 2017/2018
professor João Miguel Ascenso...

Description

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Instituto Superior Técnico Telecommunications and Informatics Engineering Electronics Engineering Network Architectures 1 test, November 21, 2017 st

Duration: 1.5 hours. Without consultation. Justify carefully all your answers. 1.

What are the lowest and highest addresses (expressed in dotted-decimal notation) of the block 10.0.0.0/22? (2 points)

2.

Consider the network of Figure 1, including three routers (r1 to r3), one point-to-point link (lp1), and two transit shared links (ls1 and ls2). The network is running OSPFv3. a) What are the LSAs describing the network topology at the LSDB, and what is their contents? Describe the contents of LSAs in terms of the router and link identifiers. Table (a) of Figure 1 indicates the OSPFv3 costs assigned to each router interface. (2 points) b) Suppose that the prefixes listed in table (b) of Figure 1 have been assigned to the links. What are the LSAs describing this addressing information at the LSDB, and what is their contents? (2 points) c) What is the IPv6 routing table of router r1? Include in the routing table the next-hop and the cost information. The link-local addresses of routers r1 and r2 are listed in table (c) of Figure 1. (1.5 points) d) Suppose that router r3 fails, and that this router was the Designated Router at link ls2. What LSA instances are flooded in the network in response to this event, and what is their contents? (1.5 points)

3.

Suppose that, in the network of Figure 1, link ls1 is the network of bridges represented in Figure 2, including four bridges (b1, b3, b5, and b8) connected by Ethernet links (eth1 to eth4). The network is running STP, and the STP costs are initially 10 in all interfaces. a) Indicate the (i) the root bridge, (ii) the root port of each non-root bridge, and (iii) the designated port at each link. (2.5 points) b) Change one interface cost (you are only allowed to change one cost), to ensure that packets sent from r1 to r2 do not cross the link between b1 and b5 (link eth1). What did you change? (1.5 points)

4.

Suppose that, in the network of Figure 1, two VLANs (VLAN 1 and VLAN 2) were configured at link ls1, and that link ls1 is the network of bridges of Figure 2. All OSPF and STP interface costs are initially 10. a) Indicate the changes in the interface costs such that traffic from r1 to ls2 crosses VLAN 1. (2.5 points)

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b) Explain how in the network of bridges of ls1 traffic from VLAN 1 is distinguished from that of VLAN 2. Be synthetic, do not use more than 3 lines in you answer. (1.5 points) 5.

Consider now that the network of Figure 1 is running RIPng. Remember that the interface costs are all equal to one in RIPng. The prefixes assigned to the links are the ones of table (b) from Figure 1. To facilitate your answer, you can refer to the prefixes assigned to lp1, ls1, and ls2, as ap1, ap2, and ap3, respectively. a) Assuming a cold start situation, indicate the contents of the first four distance vectors (announcing the prefixes) sent by the routers, if they are sent by this order: r1, r3, r2, r1. (1.5 points) b) Is the distance vector sent by one router flooded to all other routers, or only to the neighbors of the sending router? (1.5 points)

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