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

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23 Οκτ 2013 (πριν από 3 χρόνια και 7 μήνες)

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

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

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 Give an example of one IP

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

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

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


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

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

hosts can be attached to
each subnet?


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?


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

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.