Introduction to Data Communication Fall 2011
Exercises 5
What kind of IP packet does A send? What does the router R1 do to
this packet? What does router R2 do to the packets it receives?
What kind of IP packets does B receive? Give the
contents of the IP header fields involved in fragmentation in the
sent and received IP packets.
The applet "IP Fragmentation" from
the suppport page provided by the course book can be helpful.
Give, based on the routes found, the routing table for node
A. In the routing table there is, for each node the outlink to be
used and the cost of the route. The outlinks are numbered so that
the link from A to B is number 1, from A to D number 2 and from A
to C number 3.
With a program called traceroute you can find out
what routes packets really travel in the Internet. Links to many
traceroute services are to be found from the net address
http://www.traceroute.org, for example the traceroute service of Funet http://www.csc.fi/cgi-bin/nph-traceroute
or the traceroute service of ETSI
http://portal.etsi.org/webstats/traceroute.asp. Find out how packets are routed from USA or Canada to
the Computer Science Department at the University of Helsinki (cs.helsinki.fi)
or some other domain or IP address
chosen by you.
What information do you get about the routes?
How is the traceroute program really working to get that information?
Consider a datagram networks using 32-bit host addresses. Suppose a router has four links,
numbered 0 through 3, and packets are to be forwarded to the link interface as follows:
Destination Address Range Link interface
11100000 00000000 00000000 00000000
............. 0
11100000 11111111 11111111 11111111
11100001 00000000 00000000 00000000
............ 1
11100001 00000000 11111111 11111111
11100001 00000001 00000000 00000000
........... 2
11100001 11111111 11111111 11111111
otherwise 3
11001000 10010001 01010001 01010101
11100001 00000000 11000011 00111100
11100001 10000000 00010001 01110111
Consider a router that interconnects three subnets: Sub1, Sub2, and Sub3. Suppose
all of the interfaces in each of these three subnets are required to have the prefix 223.1.17.0/24. Also suppose that Sub1 is required to support up to 126 hosts or interfaces, and Sub2 and Sub3 are each required to support up to 60 interfaces. Provide three network address (of form a.b.c.d/x) that satisfy these constraints.
The network layer of host A gets from its transport layer a segment of
3000 bytes to be sent to the host B. Between the host A and B there are three networks (a, x, b) and two routers R1 and R2. The MTU (Maximum Transfer Unit) (= the size of the largest IP datagram that the network can transport) for the network a is 4000 bytes. The MTU of the network x is 1500 B and of b is 1000 B.
Suppose that the next
sequence number for A's IP packet is 100.
A - XXXXXXXXX - router - XXXXXXXXXXXX - router - XXXXXXXXXX - B
network a R1 network x R2 network b
MTU= 4000 B MTU = 1500 B MTU = 1000 B
For routing the distance vector algorithm is used. Supposing
each node in the network below, first knows only the distances to
its neighbors. What is the content of routing table of the node E
after the node E has exchanged routing information with its neighbors?
4
A --------------- B
| /|
| / |
| / |
| 5 / |
| / |
12 | / | 7
| / |
| E |
| / \ |
| / \ |
| 2 / \10 |
| / \ |
| / \ |
| / \ |
C --------------- D
1
3
B . . . . . . .F
. . . .
. . . .
3 . 1 . 4 . . 2
. . . .
. 3 . . 3 .
network A . . . . . . . D . . . . . . . .E
. . . .
. . . .
. . 2 . 2 .
2 . . . . 1
. . . .
. . . .
C . . . . . . . G
2