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Computer Networks A Systems Approach

Larry L. Peterson, Bruce S. Davie

Chapter 4

Internetworking - all with Video Answers

Educators

Chapter Questions

02:12

Problem 1

What aspect of IP addresses makes it necessary to have one address per network interface, rather than just one per host? In light of your answer, why does IP tolerate point-to-point interfaces that have nonunique addresses or no addresses?

Aman Gupta
Aman Gupta
Numerade Educator
01:04

Problem 2

Why does the Offset field in the IP header measure the offset in 8-byte units? (Hint: Recall that the Offset field is 13 bits long.)

James Kiss
James Kiss
Numerade Educator
09:14

Problem 3

Some signalling errors can cause entire ranges of bits in a packet to be overwritten by all 0 s or all 1s. Suppose all the bits in the packet including the Internet checksum are overwritten. Could a packet with all 0s or all 1s be a legal IPv4 packet? Will the Internet checksum catch that error? Why or why not?

Robin Corrigan
Robin Corrigan
Numerade Educator
01:50

Problem 4

Suppose a TCP message that contains 2048 bytes of data and 20 bytes of TCP header is passed to IP for delivery across two networks of the Internet (i.e., from the source host to a router to the destination host). The first network uses 14-byte headers and has an MTU of 1024 bytes; the second uses 8-byte headers with an MTU of 512 bytes. Each network's MTU gives the size of the largest IP datagram that can be carried in a link-layer frame. Give the sizes and offsets of the sequence of fragments delivered to the network layer at the destination host. Assume all IP headers are 20 bytes.

James Kiss
James Kiss
Numerade Educator
01:50

Problem 5

Path MTU is the smallest MTU of any link on the current path (route) between two hosts. Assume we could discover the path MTU of the path used in the previous exercise, and that we use this value as the MTU for all the path segments. Give the sizes and offsets of the sequence of fragments delivered to the network layer at the destination host.

James Kiss
James Kiss
Numerade Educator
05:05

Problem 6

Suppose an IP packet is fragmented into 10 fragments, each with a $1 \%$ (independent) probability of loss. To a reasonable approximation, this means there is a $10 \%$ chance of losing the whole packet due to loss of a fragment. What is the probability of net loss of the whole packet if the packet is transmitted twice,
(a) assuming all fragments received must have been part of the same transmission?
(b) assuming any given fragment may have been part of either transmission?
(c) Explain how use of the Ident field might be applicable here.

Amany Waheeb
Amany Waheeb
Numerade Educator
01:04

Problem 7

Suppose the fragments of Figure $4.5(\mathrm{~b})$ all pass through another router onto a link with an MTU of 380 bytes, not counting the link header. Show the fragments produced. If the packet were originally fragmented for this MTU, how many fragments would be produced?

James Kiss
James Kiss
Numerade Educator
02:53

Problem 8

What is the maximum bandwidth at which an IP host can send 576 -byte packets without having the Ident field wrap around within 60 seconds? Suppose IP's maximum segment lifetime (MSL) is 60 seconds; that is, delayed packets can arrive up to 60 seconds late but no later. What might happen if this bandwidth were exceeded?

Samriddhi Singh
Samriddhi Singh
Numerade Educator
00:30

Problem 9

ATM AAL $3 / 4$ uses fields Btag/Etag, BASize/Len, Type, SEQ, MID, Length, and CRC-10 to implement fragmentation into cells. IPv4 uses Ident, Offset, and the $M$ bit in Flags, among others. What is the IP analog, if any, for each AAL $3 / 4$ field? Does each IP field listed here have an AAL $3 / 4$ analog? How well do these fields correspond?

Sam Limsuwannarot
Sam Limsuwannarot
Numerade Educator
03:12

Problem 10

Why do you think IPv4 has fragment reassembly done at the endpoint, rather than at the next router? Why do you think IPv6 abandoned fragmentation entirely? Hint: Think about the differences between IP-layer fragmentation and link-layer fragmentation.

Khalida Dawar
Khalida Dawar
Numerade Educator
00:51

Problem 11

Having ARP table entries time out after 10-15 minutes is an attempt at a reasonable compromise. Describe the problems that can occur if the timeout value is too small or too large.

Aaron Goree
Aaron Goree
Numerade Educator
02:44

Problem 12

IP currently uses 32 -bit addresses. If we could redesign IP to use the 6 -byte MAC address instead of the 32 -bit address, would we be able to eliminate the need for ARP? Explain why or why not.

Shelby Mohamed
Shelby Mohamed
Numerade Educator
02:33

Problem 13

Suppose hosts $\mathrm{A}$ and $\mathrm{B}$ have been assigned the same IP address on the same Ethernet, on which ARP is used. B starts up after A. What will happen to A's existing connections? Explain how "self-ARP" (querying the network on startup for one's own IP address) might help with this problem.

Shelby Mohamed
Shelby Mohamed
Numerade Educator
02:05

Problem 14

Suppose an IP implementation adheres literally to the following algorithm on receipt of a packet, $\mathrm{P}$, destined for IP address $\mathrm{D}$ :
if ( Ethernet address for D is in ARP cache))
(send P)
else
(send out an ARP query for D)
(put $P$ into a queue until the response comes back)
(a) If the IP layer receives a burst of packets destined for D, how might this algorithm waste resources unnecessarily?
(b) Sketch an improved version.
(c) Suppose we simply drop P, after sending out a query, when cache lookup fails. How would this behave? (Some early ARP implementations allegedly did this.)

James Kiss
James Kiss
Numerade Educator
19:43

Problem 15

For the network given in Figure 4.48, give global distance-vector tables like those of Tables $4.5$ and $4.8$ when
(a) each node knows only the distances to its immediate neighbors.
(b) each node has reported the information it had in the preceding step to its immediate neighbors.
(c) step (b) happens a second time.

Ahmad Reda
Ahmad Reda
Numerade Educator
01:36

Problem 16

For the network given in Figure $4.49$, give global distance-vector tables like those of Tables $4.5$ and $4.8$ when
(a) each node knows only the distances to its immediate neighbors.
(b) each node has reported the information it had in the preceding step to its immediate neighbors.
(c) step (b) happens a second time.

Breanna Ollech
Breanna Ollech
Numerade Educator
01:45

Problem 17

For the network given in Figure $4.48$, show how the link-state algorithm builds the routing table for node D.

Km Neeraj
Km Neeraj
Numerade Educator
04:51

Problem 18

Suppose we have the forwarding tables shown in Table $4.12$ for nodes A and F, in a network where all links have cost 1. Give a diagram of the smallest network consistent with these tables.

Chris Trentman
Chris Trentman
Numerade Educator
04:51

Problem 19

Suppose we have the forwarding tables shown in Table $4.13$ for nodes A and F, in a network where all links have cost 1. Give a diagram of the smallest network consistent with these tables.

Chris Trentman
Chris Trentman
Numerade Educator
46:02

Problem 20

For the network in Figure $4.48$, suppose the forwarding tables are all established as in Exercise 15 and then the C-E link fails. Give
(a) the tables of $\mathrm{A}, \mathrm{B}, \mathrm{D}$, and $\mathrm{F}$ after $\mathrm{C}$ and $\mathrm{E}$ have reported the news.
(b) the tables of A and D after their next mutual exchange.
(c) the table of $\mathrm{C}$ after $\mathrm{A}$ exchanges with it.

Oswaldo Jiménez
Oswaldo Jiménez
Numerade Educator
01:49

Problem 21

Suppose a router has built up the routing table shown in Table 4.14. The router can deliver packets directly over interfaces 0 and 1 , or it can forward packets to routers $\mathrm{R} 2, \mathrm{R} 3$, or $\mathrm{R} 4 .$ Describe what the router does with a packet addressed to each of the following destinations:
(a) $128.96 .39 .10$
(b) $128.96 .40 .12$
(c) $128.96 .40 .151$
(d) $192.4 .153 .17$
(e) $192.4 .153 .90$

James Kiss
James Kiss
Numerade Educator
01:49

Problem 22

Suppose a router has built up the routing table shown in Table $4.15 .$ The router can deliver packets directly over interfaces 0 and 1 , or it can forward packets to routers $\mathrm{R} 2, \mathrm{R} 3$, or $\mathrm{R} 4$. Assume the router does the longest prefix match. Describe what the router does with a packet addressed to each of the following destinations:
(a) $128.96 .171 .92$
(b) $128.96 .167 .151$
(c) $128.96 .163 .151$
(d) $128.96 .169 .192$
(e) $128.96 .165 .121$

James Kiss
James Kiss
Numerade Educator
10:52

Problem 23

Consider the simple network in Figure $4.50$, in which A and B exchange distancevector routing information. All links have cost 1 . Suppose the A-E link fails.
(a) Give a sequence of routing table updates that leads to a routing loop between $\mathrm{A}$ and $\mathrm{B}$.
(b) Estimate the probability of the scenario in (a), assuming A and B send out routing updates at random times, each at the same average rate.
(c) Estimate the probability of a loop forming if A broadcasts an updated report within 1 second of discovering the A-E failure, and B broadcasts every 60 seconds uniformly.

Robin Corrigan
Robin Corrigan
Numerade Educator
08:32

Problem 24

Consider the situation involving the creation of a routing loop in the network of Figure $4.15$ when the A-E link goes down. List all sequences of table updates among $\mathrm{A}, \mathrm{B}$, and $\mathrm{C}$, pertaining to destination $\mathrm{E}$, that lead to the loop. Assume that table updates are done one at a time, that the split horizon technique is observed by all participants, and that A sends its initial report of E's unreachability to B before C. You may ignore updates that don't result in changes.

Lucía Guerrero
Lucía Guerrero
Numerade Educator
05:42

Problem 25

Suppose a set of routers all use the split horizon technique; we consider here under what circumstances it makes a difference if they use poison reverse in addition.
(a) Show that poison reverse makes no difference in the evolution of the routing loop in the two examples described in Section 4.2.2, given that the hosts involved use split horizon.
(b) Suppose split horizon routers $\mathrm{A}$ and $\mathrm{B}$ somehow reach a state in which they forward traffic for a given destination $X$ toward each other. Describe how this situation will evolve with and without the use of poison reverse.
(c) Give a sequence of events that leads $\mathrm{A}$ and $\mathrm{B}$ to a looped state as in (b), even if poison reverse is used. Hint: Suppose B and A connect through a very slow link. They each reach $X$ through a third node, $C$, and simultaneously advertise their routes to each other.

Carson Merrill
Carson Merrill
Numerade Educator
01:37

Problem 26

Hold-down is another distance-vector loop-avoidance technique, whereby hosts ignore updates for a period of time until link failure news has had a chance to propagate. Consider the networks in Figure $4.51$, where all links have cost 1 , except E-D with cost $10 .$ Suppose that the E-A link breaks and B reports its loopforming E route to A immediately afterward (this is the false route, via A). Specify the details of a hold-down interpretation, and use this to describe the evolution of the routing loop in both networks. To what extent can hold down prevent the loop in the EAB network without delaying the discovery of the alternative route in the EABD network?

Adam Conner
Adam Conner
Numerade Educator
04:21

Problem 27

Consider the network in Figure $4.52$, using link-state routing. Suppose the B-F link fails, and the following then occur in sequence:
(a) Node $\mathrm{H}$ is added to the right side with a connection to $\mathrm{G}$.
(b) Node D is added to the left side with a connection to C.
(c) A new link D-A is added.
The failed B-F link is now restored. Describe what link-state packets will flood back and forth. Assume that the initial sequence number at all nodes is 1 , and that no packets time out, and that both ends of a link use the same sequence number in their LSP for that link, greater than any sequence number either used before.

Robin Corrigan
Robin Corrigan
Numerade Educator
01:36

Problem 28

Give the steps as in Table $4.9$ in the forward search algorithm as it builds the routing database for node $\mathrm{A}$ in the network shown in Figure 4.53.

Khoobchandra Agrawal
Khoobchandra Agrawal
Numerade Educator
05:12

Problem 29

Give the steps as in Table $4.9$ in the forward search algorithm as it builds the routing database for node $\mathrm{A}$ in the network shown in Figure 4.54.

M Hassan Anwar
M Hassan Anwar
Numerade Educator
04:30

Problem 30

Suppose that nodes in the network shown in Figure $4.55$ participate in link-state routing, and C receives contradictory LSPs: One from A arrives claiming the A-B link is down, but one from B arrives claiming the A-B link is up.
(a) How could this happen?
(b) What should C do? What can C expect?
Do not assume that LSPs contain any synchronized timestamp.

Brian Lin
Brian Lin
Numerade Educator
02:05

Problem 31

Consider the network shown in Figure $4.56$, in which horizontal lines represent transit providers and numbered vertical lines are interprovider links.
(a) How many routes to P could provider Q's BGP speakers receive?
(b) Suppose $Q$ and $P$ adopt the policy that outbound traffic is routed to the closest link to the destination's provider, thus minimizing their own cost. What paths will traffic from host $\mathrm{A}$ to host $\mathrm{B}$ and from host $\mathrm{B}$ to host $\mathrm{A}$ take?
(c) What could $Q$ do to have the $B \longrightarrow A$ traffic use the closer link 1 ?
(d) What could $Q$ do to have the $B \longrightarrow A$ traffic pass through $R$ ?

Akash M
Akash M
Numerade Educator
00:36

Problem 32

Give an example of an arrangement of routers grouped into autonomous systems so that the path with the fewest hops from a point A to another point B crosses the same AS twice. Explain what BGP would do with this situation.

WZ
Wen Zheng
Numerade Educator
01:36

Problem 33

Let $A$ be the number of autonomous systems on the Internet, and let $D$ (for diameter) be the maximum AS path length.
(a) Give a connectivity model for which $D$ is of order $\log A$ and another for which $D$ is of order $\sqrt{A}$.
(b) Assuming each AS number is 2 bytes and each network number is 4 bytes, give an estimate for the amount of data a BGP speaker must receive to keep track of the AS path to every network. Express your answer in terms of $A, D$, and the number of networks $N$.

Breanna Ollech
Breanna Ollech
Numerade Educator
46:02

Problem 34

Suppose IP routers learned about IP networks and subnets the way Ethernet learning bridges learn about hosts: by noting the appearance of new ones and the interface by which they arrive. Compare this with existing distance-vector router learning
(a) for a leaf site with a single attachment to the Internet, and
(b) for internal use at an organization that did not connect to the Internet.
Assume that routers only receive new-network notices from other routers, and that the originating routers receive their IP network information via configuration.

Oswaldo Jiménez
Oswaldo Jiménez
Numerade Educator
01:35

Problem 35

IP hosts that are not designated routers are required to drop packets misaddressed to them, even if they would otherwise be able to forward them correctly. In the absence of this requirement, what would happen if a packet addressed to IP address A were inadvertently broadcast at the link layer? What other justifications for this requirement can you think of?

James Kiss
James Kiss
Numerade Educator
03:22

Problem 36

Read the man page or other documentation for the Unix/Windows utility netstat. Use netstat to display the current IP routing table on your host. Explain the purpose of each entry. What is the practical minimum number of entries?

Jennifer Stoner
Jennifer Stoner
Numerade Educator
01:19

Problem 37

Use the Unix utility traceroute (Windows tracert) to determine how many hops it is from your host to other hosts in the Internet (e.g., cs.princeton.edu or www.cisco.com). How many routers do you traverse just to get out of your local site? Read the man page or other documentation for traceroute and explain how it is implemented.

James Kiss
James Kiss
Numerade Educator
02:22

Problem 38

What will happen if traceroute is used to find the path to an unassigned address? Does it matter if the network portion or only the host portion is unassigned?

Shelby Mohamed
Shelby Mohamed
Numerade Educator
01:19

Problem 39

A site is shown in Figure 4.57. R1 and R2 are routers; R2 connects to the outside world. Individual LANs are Ethernets. RB is a bridge router; it routes traffic addressed to it and acts as a bridge for other traffic. Subnetting is used inside the site; ARP is used on each subnet. Unfortunately, host A has been misconfigured and doesn't use subnets. Which of $\mathrm{B}, \mathrm{C}, \mathrm{D}$ can $\mathrm{A}$ reach?

James Kiss
James Kiss
Numerade Educator
03:33

Problem 40

An organization has a class C network $200.1 .1$ and wants to form subnets for four departments, with hosts as follows:
A 72 hosts
B 35 hosts
C 20 hosts
D 18 hosts
There are 145 hosts in all.
(a) Give a possible arrangement of subnet masks to make this possible.
(b) Suggest what the organization might do if department D grows to 34 hosts.

Akash M
Akash M
Numerade Educator
03:33

Problem 41

Suppose hosts $\mathrm{A}$ and $\mathrm{B}$ are on an Ethernet LAN with class C IP network address $200.0 .0 .$ It is desired to attach a host $\mathrm{C}$ to the network via a direct connection to B (see Figure $4.58$ ). Explain how to do this with subnets; give sample subnet assignments. Assume that an additional network address is not available. What does this do to the size of the Ethernet LAN?

Akash M
Akash M
Numerade Educator
01:19

Problem 42

An alternative method for connecting host $\mathrm{C}$ in Exercise 41 is to use proxy ARP and routing: $\mathrm{B}$ agrees to route traffic to and from $\mathrm{C}$ and also answers ARP queries for Creceived over the Ethernet.
(a) Give all packets sent, with physical addresses, as A uses ARP to locate and then send one packet to $\mathrm{C}$.
(b) Give B's routing table. What peculiarity must it contain?

James Kiss
James Kiss
Numerade Educator
02:44

Problem 43

Propose a plausible addressing plan for IPv6 that runs out of bits. Specifically, provide a diagram such as Figure $4.33$, perhaps with additional ID fields, that adds up to more than 128 bits, together with plausible justifications for the size of each field. You may assume fields are divided on byte boundaries and that the InterfacelD is 64 bits. Hint: Consider fields that would approach maximum allocation only under unusual circumstances. Can you do this if the InterfacelD is 48 bits?

Shelby Mohamed
Shelby Mohamed
Numerade Educator
01:19

Problem 44

Suppose two subnets share the same physical LAN; hosts on each subnet will see the other subnet's broadcast packets.
(a) How will DHCP fare if two servers, one for each subnet, coexist on the shared LAN? What problems might $[d o !]$ arise?
(b) Will ARP be affected by such sharing?

James Kiss
James Kiss
Numerade Educator
01:26

Problem 45

Table $4.16$ is a routing table using CIDR. Address bytes are in hexadecimal. The notation "/12" in C4.50.0.0/12 denotes a netmask with 12 leading 1 bits, that is, FF.F0.0.0. Note that the last three entries cover every address and thus serve in lieu of a default route. State to what next hop the following will be delivered.
(a) C4.5E.13.87
(b) C4.5E.22.09
(c) C3.41.80.02
(d) $5 \mathrm{E} .43 .91 .12$
(e) C4.6D.31.2E
(f) C4.6B.31.2E

James Kiss
James Kiss
Numerade Educator
01:26

Problem 46

Table $4.17$ is a routing table using CIDR. Address bytes are in hexadecimal. The notation "/12" in C4.50.0.0/12 denotes a netmask with 12 leading 1 bits, that is, FFFO.0.0. State to what next hop the following will be delivered:
(a) C4.4B.31.2E
(b) C4.5E.05.09
(c) C4.4D.31.2E
(d) C4.5E.03.87
(e) C4.5E.7F.12
(f) C4.5E.D1.02

James Kiss
James Kiss
Numerade Educator
01:31

Problem 47

Suppose $\mathrm{P}, \mathrm{Q}$, and $\mathrm{R}$ are network service providers, with respective CIDR address allocations (using the notation of Exercise 45) C1.0.0.0/8, C2.0.0.0/8, and $C 3.0 .0 .0 / 8$. Each provider's customers initially receive address allocations that are a subset of the provider's. P has the following customers:
PA, with allocation C1.A3.0.0/16, and
PB, with allocation C1.B0.0.0/12.
Q has the following customers:
QA, with allocation C2.0A.10.0/20, and
$\mathrm{QB}$, with allocation $\mathrm{C} 2.0 \mathrm{~B} .0 .0 / 16$.
Assume there are no other providers or customers.
(a) Give routing tables for $\mathrm{P}, \mathrm{Q}$, and $\mathrm{R}$, assuming each provider connects to both of the others.
(b) Now assume $P$ is connected to $Q$ and $Q$ is connected to $R$, but $P$ and $R$ are not directly connected. Give tables for $\mathrm{P}$ and $\mathrm{R}$.
(c) Suppose customer PA acquires a direct link to Q, and QA acquires a direct link to $\mathrm{P}$, in addition to existing links. Give tables for $\mathrm{P}$ and $\mathrm{Q}$, ignoring $\mathrm{R}$.

Aman Gupta
Aman Gupta
Numerade Educator
03:58

Problem 48

In the previous problem, assume each provider connects to both others. Suppose customer PA switches to provider $Q$ and customer $Q B$ switches to provider $R$. Use the CIDR longest match rule to give routing tables for all three providers that allow $P A$ and $Q B$ to switch without renumbering.

Abigail Martyr
Abigail Martyr
Numerade Educator
01:26

Problem 49

Suppose most of the Internet uses some form of geographical addressing, but that a large international organization has a single IP network address and routes its internal traffic over its own links.
(a) Explain the routing inefficiency for the organization's inbound traffic inherent in this situation.
(b) Explain how the organization might solve this problem for outbound traffic.
(c) For your method above to work for inbound traffic, what would have to happen?
(d) Suppose the large organization now changes its addressing to separate geographical addresses for each office. What will its internal routing structure have to look like if internal traffic is still to be routed internally?

Samriddhi Singh
Samriddhi Singh
Numerade Educator
01:07

Problem 50

The telephone system uses geographical addressing. Why do you think this wasn't adopted as a matter of course by the Internet?

Abhishek Jana
Abhishek Jana
Numerade Educator
05:42

Problem 51

Suppose a site A is multihomed, in that it has two Internet connections from two different providers, $P$ and $Q$. Provider-based addressing as in Exercise 47 is used, and $A$ takes its address assignment from $P$. $Q$ has a CIDR longest match routing entry for $A$.
(a) Describe what inbound traffic might flow on the A-Q connection. Consider cases where $Q$ does and does not advertise $A$ to the world using $B G P$.
(b) What is the minimum advertising of its route to $\mathrm{A}$ that $\mathrm{Q}$ must do in order for all inbound traffic to reach $\mathrm{A}$ via $\mathrm{Q}$ if the $\mathrm{P}-\mathrm{A}$ link breaks?
(c) What problems must be overcome if $\mathrm{A}$ is to use both links for its outbound traffic?

Carson Merrill
Carson Merrill
Numerade Educator
02:49

Problem 52

An ISP with a class $\mathrm{B}$ address is working with a new company to allocate it a portion of address space based on CIDR. The new company needs IP addresses for machines in three divisions of its corporate network: Engineering, Marketing, and Sales. These divisions plan to grow as follows: Engineering has 5 machines as of the start of year 1 and intends to add 1 machine every week; Marketing will never need more than 16 machines; and Sales needs 1 machine for every two clients. As of the start of year 1, the company has no clients, but the sales model indicates that by the start of year 2 , the company will have six clients and each week thereafter gets one new client with probability $60 \%$, loses one client with probability $20 \%$, or maintains the same number with probability $20 \%$.
(a) What address range would be required to support the company's growth plans for at least seven years if marketing uses all 16 of its addresses and the sales and engineering plans behave as expected?
(b) How long would this address assignment last? At the time when the company runs out of address space, how would the addresses be assigned to the three groups?
(c) If CIDR addressing were not available for the seven-year plan, what options would the new company have in terms of getting address space?

Bailey Brooks
Bailey Brooks
Numerade Educator
01:38

Problem 53

Propose a lookup algorithm for a CIDR fowarding table that does not require a linear search of the entire table to find the longest match.

Victor Salazar
Victor Salazar
Numerade Educator
01:49

Problem 54

Suppose a network $N$ within a larger organization $A$ acquires its own direct connection to an Internet service provider, in addition to an existing connection via A. Let $R 1$ be the router connecting $N$ to its own provider, and let $R 2$ be the router connecting $N$ to the rest of $A$.
(a) Assuming $\mathrm{N}$ remains a subnet of A, how should R1 and R2 be configured? What limitations would still exist with N's use of its separate connection? Would A be prevented from using N's connection? Specify your configuration in terms of what R1 and R2 should advertise, and with what paths. Assume a BGP-like mechanism is available.
(b) Now suppose $N$ gets its own network number; how does this change your answer in (a)?
(c) Describe a router configuration that would allow A to use N's link when its own link is down.

Raj Bala
Raj Bala
Numerade Educator
03:01

Problem 55

Consider the example internet shown in Figure $4.59$, in which sources $\mathrm{D}$ and $\mathrm{E}$ send packets to multicast group $\mathrm{G}$, whose members are shaded in gray. Show the shortest-path multicast trees for each source.

Thomas Thompson
Thomas Thompson
Numerade Educator
View

Problem 56

Consider the example internet shown in Figure $4.60$ in which sources $\mathrm{S} 1$ and $\mathrm{S} 2$ send packets to multicast group $\mathrm{G}$, whose members are shaded in gray. Show the shortest-path multicast trees for each source.

Lainey Roebuck
Lainey Roebuck
Numerade Educator
01:22

Problem 57

Suppose host $\mathrm{A}$ is sending to a multicast group; the recipients are leaf nodes of a tree rooted at A with depth $N$ and with each nonleaf node having $k$ children; there are thus $k^{N}$ recipients.
(a) How many individual link transmissions are involved if A sends a multicast message to all recipients?
(b) How many individual link transmissions are involved if A sends unicast messages to each individual recipient?
(c) Suppose A sends to all recipients, but some messages are lost and retransmission is necessary. Unicast retransmissions to what fraction of the recipients is equivalent, in terms of individual link transmissions, to a multicast retransmission to all recipients?

Erika Bustos
Erika Bustos
Numerade Educator
01:36

Problem 58

Determine whether or not the following IPv6 address notations are correct.
(a) ::0F53:6382:AB00:67DB:BB27:7332
(b) $7803: 42 \mathrm{~F} 2::: 88 \mathrm{EC}: \mathrm{D} 4 \mathrm{BA}: \mathrm{B} 75 \mathrm{D}: 11 \mathrm{CD}$
(c) ::4BA8:95CC:DB97:4EAB
(d) $74 \mathrm{DC}: 02 \mathrm{BA}$
(e) ::00FF: $128.112 .92 .116$

James Kiss
James Kiss
Numerade Educator
09:33

Problem 59

Determine if your site is connected to the MBone. If so, investigate and experiment with any MBone tools, such as sdr, vat, and vic.

Sajay Krishnan Paruthiyil
Sajay Krishnan Paruthiyil
Numerade Educator
04:21

Problem 60

MPLS labels are usually 20 bits long. Explain why this provides enough labels when MPLS is used for destination-based forwarding.

Jennifer Stoner
Jennifer Stoner
Numerade Educator
02:52

Problem 61

MPLS has sometimes been claimed to improve router performance. Explain why this might be true, and suggest reasons why in practice this may not be the case.

Kaylee Mcclellan
Kaylee Mcclellan
Numerade Educator
01:22

Problem 62

Assume that it takes 32 bits to carry each MPLS label that is added to a packet when the "shim" header of Figure $4.42$ (b) is used.
(a) How many additional bytes are needed to tunnel a packet using the MPLS techniques described in Section 4.5.3?
(b) How many additional bytes are needed, at a minimum, to tunnel a packet using an additional IP header as described in Section 4.1.8?
(c) Calculate the efficiency of bandwidth usage for each of the two tunneling approaches when the average packet size is 300 bytes. Repeat for 64-byte packets. Bandwidth efficiency is defined as (payload bytes carried) $\div$ (total bytes carried).

Erika Bustos
Erika Bustos
Numerade Educator
01:26

Problem 63

RFC 791 describes the Internet Protocol and includes two options for source routing. Describe three disadvantages of using IP source route options compared to using MPLS for explicit routing. (Hint: The IP header including options may be at most 15 words long.)

Samriddhi Singh
Samriddhi Singh
Numerade Educator