Sub-netting 1. Consider a router that interconnects three subnets ...

dimerusticNetworking and Communications

Oct 23, 2013 (3 years and 11 months ago)

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Sub
-
netting



1. Consider a router that interconnects three subnets: Subnet1, Subnet2 and
Subnet3.

Suppose al of the interfaces in each subnet are required to have the prefix

223.1.17/24. Also suppose that Subnet1 is required to support up to 125
inte
rfaces

and Subnet2 and Subnet 3 are each required to support up to 60 interfaces.

Provide 3 network addresses (of the form a.b.c.d/x) that satisfy these constraints.

2. Consider a network with prefix 101.101.101.64/26. Give an example of one IP

address
(of the form xxx.xxx.xxx.xxx) that can be assigned to this network.

Suppose an ISP owns the block of addresses of the form 101.101.128/17.
Suppose

it wants to create four subnets from this block, each block having the same

number of IP addresses. What
are the prefixes (of form a.b.c.d/x) for the four

subnets?

3. An ISP wants to divide a network with address 192.168.40.0 into two networks
of

equal size. Is there a problem with this? (hint, first and last addresses). How
many

hosts can be attached to
each subnet?



MTU/Fragmentation



4. Suppose datagrams are limited to 1500 bytes (including IP header) between

source host A and destination host B. Assuming a 20 byte IP header, how many

datagrams would be required to send an mp3 consisting of 4 mill
ion bytes?



Routing delay

5. In packet switched networks, each packet will experience delay end to end. If

there are j identical links and routers end to end derive an expression for the total

delay using the following constants: Packet size P, link d
ata rate r, queuing delay

q, processing delay p. How long does it take to send i packets over this network?

What would the expression be for different links and routers?


Advanced



1. Play detective: after monitoring IP traffic on a local area network
for 10 minutes
one evening, someone notices that all frames destined for machine A carry IP
datagrams that have destination equal to A’s IP address, while all frames
destined for machine B carry IP datagrams with destination not equal to B’s IP
address. U
sers report that both A and B can communicate. Explain.

2. How could you change the IP datagram format to support high
-
speed packet

switching at routers? Hint: a router must recompute a header checksum after

decrementing the TTL field.


3. A classful ro
uting table has four buckets in the table and single entry for default

routing. The first bucket is for host
-
specific routing with 10 entries. The second

bucket is for class A blocks with 50 entries. The third bucket is for class B blocks

with 400 entri
es. The fourth bucket is for class C blocks with 2000 entries. Find
the

average number of table lookups for each of the following cases:

(a) A packet with host
-
specific route has arrived.

(b) A packet with a class A address has arrived.

(c) A packet wi
th a class B address has arrived.

(d) A packet with a class C address has arrived.